A ae ST io » LA. | 7s) ans ete J HEMISPHERE ® M 9 a : + * 4 f ‘ oan a 5 Pf ne h+ i . ro “p's eae: . ea i As CORNELL UNIVERSITY LIBRARY wow yg s. BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN 1891 BY HENRY WILLIAMS SAGE Cornell University Lib: QE 881.843 woe ii | 3 1924 004 446 211 essr A HISTORY OF LAND MAMMALS IN THE WESTERN HEMISPHERE THE MACMILLAN COMPANY NEW YORK : BOSTON - CHICAGO - DALLAS ATLANTA - SAN FRANCISCO MACMILLAN & CO., Limrrep LONDON + BOMBAY = CALCUTTA MELBOURNE THE MACMILLAN CO. OF CANADA, Lrp. TORONTO *9OBI ULBYINOS oy} JO on} Uo sAVY ABUT sv ‘ssaTITEY STQUBYdo[a aYL *(2quinjoo| spydajq) yuRYydey— ue Jo ssvo1ed ay} UO (snII.ULOLt{DI uopopiwg |) IIsty, 4}Ooj-s1qeg| pue (Snip| StUDD) SOATOAA JUTTD| : BIUIOJ]TVO ULYYNOS UI [OOd-1v} 9UBI0}SId[g YW -— ‘TOMIdSLLNOUT A HISTORY OF LAND MAMMALS IN THE WESTERN HEMISPHERE BY WILLIAM B. SCOTT Pu.D. (Heidelberg), Hon. D.Sc. (Harvard & Oxford), LL.D. (Univ. of Pennsylvania) BLAIR PROFESSOR OF GEOLOGY AND PALZONTOLOGY IN PRINCETON UNIVERSITY ILLUSTRATED WITH 32 PLATES AND MORE THAN 100 DRAWINGS BY BRUCE HORSFALL » Neto Bork THE MACMILLAN COMPANY 1913 All rights reserved EN, CoryRicut, 1913, By THE MACMILLAN COMPANY. Set up and electrotyped. Published November, 1913, Norwood Press J. 8. Cushing Co. — Berwick & Smith Co. Norwood, Mass., U.S.A. DE Dedicated TO MY CLASSMATES HENRY FAIRFIELD OSBORN anp FRANCIS SPEIR IN MEMORY OF A NOTABLE SUMMER AFTERNOON IN 1876 AND IN TOKEN OF FORTY YEARS’ UNCLOUDED FRIENDSHIP Speak to the earth and it shall teach thee. — Jos, xii, 8. Can these bones live ? — EZEKIEL, xxxvii, 3. PREFACE OnE afternoon in June, 1876, three Princeton undergraduates were lying under the trees on the canal bank, making a languid pretence of preparing for an examination. Suddenly, one of the trio remarked: “I have been reading an old magazine article which describes a fossil-collecting expedition in the West; why can’t we get up something of the kind?” The others replied, as with one voice, “ We can; let’s do it.” This seemingly idle talk was, for Osborn and myself, a momentous one, for it completely changed the careers which, as we then believed, had been mapped out for us. The random suggestion led directly to the first of the Princeton paleontological expeditions, that of 1877, which took us to the “ Bad Lands” of the Bridger region in southwestern Wyoming. The fascination of discovering and exhuming with our own hands the remains of the curious creatures which once inhabited North America, but became extinct ages ago, has proved an enduring delight. It was the wish to extend something of this fascinating interest to a wider circle, that occasioned the preparation of this book. The western portion of North America has preserved a marvel- lous series of records of the successive assemblages of animals which once dwelt in this continent, and in southernmost South America an almost equally complete record was made of the strange animals of that region. For the last half-century, or more, many workers haye codperated to bring this long-vanished world to light and to decipher and interpret the wonderful story of mammalian development in the western hemisphere. The task of making this history intelligible, not to say interesting, to the layman, has been one of formidable difficulty, for it is recorded in the successive modifications of the bones and teeth, and without some knowledge of osteology, these records are in an unknown ix x PREFACE tongue. To meet this need, Chapter III gives a sketch of the mammalian skeleton and dentition, which the reader may use as the schoolboy uses a vocabulary to translate his Latin exercise, referring to it from time to time, as may be necessary to make clear the descriptions of the various mammalian groups. Techni- cal terms have been avoided as far as possible, but, unfortunately, it is not practicable to dispense with them altogether. The appended glossary will, it is hoped, minimize the inconvenience. No one who has not examined it, can form any conception of the enormous mass and variety of material, illustrating the history of American mammals, which has already been gathered into the various museums. A full account of this material would require many volumes, and one of the chief problems in the preparation of this book has been that of making a proper selection of the most instructive and illuminating portions of the long and com- plicated story. Indeed, so rapid is the uninterrupted course of discovery, that parts of the text became antiquated while in the press and had to be rewritten. As first prepared, the work proved to be far too long and it was necessary to excise several chapters, for it seemed better to cover less ground than to make the entire history hurried and superficial. The plan of treatment adopted involves a considerable amount of repetition, but this is perhaps not a disadvantage, since the same facts are considered from different points of view. The facts which are here brought together have been ascer- tained by many workers, and I have borrowed with the greatest freedom from my fellow labourers in the field of paleontology. As every compiler of a manual finds, it is not feasible to attribute the proper credit to each discoverer. Huxley has so well explained the situation in the preface to his “ Anatomy of Vertebrated Ani- mals,” that I may be permitted to borrow his words: “I have intentionally refrained from burdening the text with references ; and, therefore, the reader, while he is justly entitled to hold me responsible for any errors he may detect, will do well to give me no credit for what may seem original, unless his knowledge is sufficient to render him a competent judge on that head.” PREFACE xi A book of this character is obviously not the proper place for polemical discussions of disputed questions. Whenever, there- fore, the views expressed differ widely from those maintained by other paleontologists, I have attempted no more than to state, as fairly as I could, the alternative interpretations and my own choice between them. Any other course was forbidden by the limitations of space. It is a pleasure to give expression to my sincere sense of grati- tude to the many friends who have helped me in an unusually laborious undertaking. Professor Osborn and Dr. Matthew have placed at my disposal the wonderful treasures of the American Museum of Natural History in New York and in the most liberal manner have supplied me with photographs and specimens for drawings, as well as with information regarding important dis- coveries which have not yet been published. Dr. W. J. Holland, Director of the Carnegie Museum in Pittsburgh, has likewise gen- erously provided many photographs from the noble collection under his charge, kindly permitting the use of material still undescribed. To Professor Charles Schuchert, of Yale University, I am also indebted for several photographs. The figures of existing animals are almost all from photographs taken in the New York and London zodlogical gardens, and I desire to thank Director Hornaday, of the Bronx Park, and Mr. Peacock, of the London garden, for the very kind manner in which they have procured these illustrations for my use. The photographs have been modified by painting out the backgrounds of cages, houses, and the like, so as to give a less artificial appear- ance to the surroundings. To my colleagues at Princeton I am under great obligations for much valuable counsel and assistance. Professor Gilbert van Ingen has prepared the maps and diagrams and Dr. W. J. Sinclair has devoted much labour and care to the illustrations and has also read the proofs. Both of these friends, as also Professors C. H. Smyth and E. G. Conklin and Drs. Farr and McComas, have read various parts of the manuscript and made many helpful sugges- tions in dealing with the problems of treatment and presentation. xii PREFACE For thirteen years past I have been engaged in the study of the great collections of fossil mammals, gathered in Patagonia by the lamented Mr. Hatcher and his colleague, Mr. Peterson, now of the Carnegie Museum. This work made it necessary for me to visit the museums of the Argentine Republic, which I did in 1901, and was there received with the greatest courtesy and kind- ness by Dr. F. Moreno, Director, and Dr. Santiago Roth, of the La Plata Museum, and Dr. F. Ameghino, subsequently Director of the National Museum at Buenos Aires. To all of these gentle- men the chapters on the ancient life of South America are much indebted, especially to Dr. Ameghino, whose untimely death was a great loss to science. It is earnestly to be hoped that the heroic story of his scientific career may soon be given to the world. Finally, I desire to thank Mr. Horsfall for the infinite pains and care which he has expended upon the illustrations for the work, to which so very large a part of its value is due. While the book is primarily intended for the lay reader, I can- not but hope that it may also be of service to many zodlogists, who have been unable to keep abreast of the flood of palonto- logical discovery and yet wish to learn something of its more significant results. How far I have succeeded in a most difficult task must be left to the judgment of such readers. Princeton, N.J., June 1, 1918. CONTENTS CHAPTER I METHODS OF INVESTIGATION— GEOLOGICAL . . 3 ‘ . on CHAPTER II METHODS OF INVESTIGATION — PALEZONTOLOGICAL 7 . : . 29 CHAPTER III THE CLASSIFICATION OF THE MAMMALIA ‘ z : : $ . 50 CHAPTER IV Tue SKELETON AND TEETH OF MAMMALS. . <3 zi . 61 CHAPTER V THE GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS IN CENOZOIC TIMEs . : 5 5 - ? £ ‘ ‘ 3 5 . 99 CHAPTER VI Tue GEOGRAPHICAL DISTRIBUTION OF MAMMALS . . : : - 135 CHAPTER VII Tue SuccEssIVE MAMMALIAN Faunas OF NortH AND SoutH AMERICA 192 CHAPTER VIII History OF THE PERISSODACTYLA . : - ‘ Fi < ‘ . 288 CHAPTER IX History OF THE ARTIODACTYLA . ‘ ‘ ‘ a é : . 358 CHAPTER X History OF THE PROBOSCIDEA z : ‘ x ‘ 5 é . 422 xiii xiv History History History History History HIsTory History OF OF OF OF OF OF OF CONTENTS CHAPTER XI THE fAMBLYPODA AND {CONDYLARTHRA . CHAPTER XII THE tToxoponTia (oR fNOTOUNGULATA) CHAPTER XIII THE {LITOPTERNA AND tASTRAPOTHERIA . CHAPTER XIV THE CARNIVORA CHAPTER XV THE PRIMATES CHAPTER XVI THE EDENTATA CHAPTER XVII THE MARSUPIALIA CHAPTER XVIII Moves oF MAMMALIAN EVOLUTION GLOSSARY INDEX t+ Extinct. PAGE 443 461 489 516 577 589 624 645 665 675 A HISTORY OF LAND MAMMALS IN THE WESTERN HEMISPHERE A HISTORY OF LAND MAMMALS IN THE WESTERN HEMISPHERE CHAPTER I METHODS OF INVESTIGATION — GEOLOGICAL THE term Mammal has no exact equivalent in the true vernacular of any modern language, the word itself, like its equivalents, the French Mammifére and the German Séduge- thier, being entirely artificial. As a name for the class Linneus adopted the term Mammalia, which he formed from the Latin mamma (i.e. teat) to designate those animals which suckle their young; hence the abbreviated form Mammal, which has been naturalized as an English word. ‘‘ Beast,’ as employed in the Bible, and ‘‘Quadruped”’ are not quite the same as mammal, for they do not include the marine forms, such as whales, dolphins, seals, walruses, or the flying bats, and they are habitually used in contradistinction to Man, though Man and all the forms mentioned are unquestionably mammals. In attempting to frame a definition of the term Mammal, it is impossible to avoid technicalities altogether, for it is the complete unity of plan and structure which justifies the in- clusion of all the many forms that differ so widely in habits and appearance. Mammals are air-breathing vertebrates, which are warm-blooded and have a 4-chambered heart; the body cavity is divided into pleural and abdominal chambers by a diaphragm ; except in the lowest division of the class, the young are brought forth alive and are always suckled, the milk glands being universal throughout the class. In the great majority of mammals the body B 1 2 LAND MAMMALS IN THE WESTERN HEMISPHERE is clothed with hair; a character found in no other animals. In a few mammals the skin is naked, and in still fewer there is a partial covering of scales. The list of characters common to all mammals, which distinguish them from other animals, might be indefinitely extended, for it includes all the organs and tissues of the body, the skeletal, muscular, digestive, ner- vous, circulatory, and reproductive systems, but the two or three more obvious or significant features above selected will suffice for the purposes of definition. While the structural plan is the same throughout the entire class, there is among mammals a wonderful variety of form, size, appearance, and adaptation to special habits. It is as though a musician had taken a single theme and developed it into endless variations, preserving an unmistakable unity through all the changes. Most mammals are terrestrial, living, that is to say, not only on the land, but on the ground, and are herbivorous in habit, subsisting chiefly or exclusively upon vegetable substances, but there are many departures from this mode of life. It should be explained, however, that the term terrestrial is frequently used in a more comprehensive sense for all land mammals, as distinguished from those that are aquatic or marine. Monkeys, Squirrels, Sloths and Opossums are examples of the numerous arboreal mammals, whose structure is modified to fit them for living and sleeping in the trees, and in some, such as the Sloths, the modification is carried so far that the creature is almost helpless on the ground. An- other mode of existence is the burrowing or fossorial, the animal living partly or mostly, or even entirely underground, a typical instance of which is the Mole. The Beaver, Muskrat and Otter, to mention only a few forms, are aquatic and spend most of their life in fresh waters, though perfectly able to move about on theland. Marine mammals, such as the Seals and Whales, have a greatly modified structure which adapts them to life in the sea. Within the limits of each of these categories we may note METHODS — GEOLOGICAL 3 that there are many degrees of specialization or adaptation to particular modes of life. Thus, for example, among the marine mammals, the Whales and their allies, Porpoises, etc., are so completely adapted to a life in the seas that they cannot come upon the land, and even stranding is fatal to them, while the Seals frequently land and move about upon the shore. It should further be observed that mammals of the most diverse groups are adapted to similar modes of existence. Thus in one ‘natural group or order of related forms, occur terrestrial, burrow- ing, arboreal and aquatic members, and the converse state- ment is of course equally true, that animals of similar life- habits are not necessarily related to one another, and very frequently, in fact, are not so related. Among the typically marine mammals, for example, there are at least three and probably four distinct series, which have independently be- - come adapted to life in the sea. Before attempting to set forth an outline of what has been learned regarding the history of mammalian life in the western hemisphere, it is essential to give the reader some con- ception of the manner in which that knowledge has been ob- tained. Without such an understanding of the methods em- ployed in the investigation the reader can only blindly accept or as blindly reject what purports to be the logical inference from well-established evidence. How is that evidence to be discovered ? and how may trustworthy conclusions be derived from it? The first and most obvious step is to gather all possible in- formation concerning the mammals of the present day, their structure (comparative anatomy), functions (physiology), and their geographical arrangement. This latter domain, of the geographical distribution of mammals, is one of peculiar signif- icance. Not only do the animals of North America differ radi- cally from those of Central and South America, but within the limits of each continent are more or less well-defined areas, 4 LAND MAMMALS IN THE WESTERN HEMISPHERE the animals of which differ in a subordinate degree from those of other areas. The study of the modern world, however, would not of itself carry us very far toward the goal of our inquiries, which is an explanation, not merely a statement, of the facts. The present order of things is the outcome of an illimitably long sequence of events and can be understood only in proportion to our knowledge of the past. In other words, it is necessary to treat the problems involved in our inquiry historically; to trace the evolution of the different mammalian groups from their simpler beginnings to the more complex and highly specialized modern forms; to determine, so far as that may be done, the place of origin of each group and to follow out their migrations from continent to continent. While we shall deal chiefly, almost exclusively, with the mammals of the New World, something must be said regard- ing those of other continents, for, as will be shown in the sequel, both North and South America have, at one time or another, been connected with various land-masses of the eastern hemi- sphere. By means of those land-connections, there has been an interchange of mammals between the different continents, and each great land-area of the recent world contains-a more or less heterogeneous assemblage of forms of very diverse places of origin. Indeed, migration from one region to another has played a most important part in bringing about the present distribution of living things. From what has already been learned as to the past life of the various continents and their shifting connections with one another, it is now feasible to analyze the mammalian faunas of most of them and to separate the indigenous from the immigrant elements. Among the latter may be distinguished those forms which are the much modified descendants of ancient migrants from those which arrived at a much later date and have undergone but little change. To take a few examples from North America, it may be said that the Bears, Moose, Caribou and Bison are late migrants from the Old World; that the Virginia and Black- METHODS — GEOLOGICAL 5 tailed Deer and the Prong-horned Antelope are of Old World origin, but their ancestors came in at a far earlier period and the modern species are greatly changed.from the ancestral migrants. The Armadillo of Texas and the Canada Porcupine are almost the only survivors, north of Mexico, of the great migration of South American mammals which once invaded the northern continent. On the other hand, the raccoons and several families of rodents are instances of indigenous types which may be traced through a long American ancestry. Fully to comprehend the march of mammalian development, it thus becomes necessary to reconstruct, at least in outline, the geography of the successive epochs through which the developmental changes have taken place, the connections and separations of land-masses, the rise of mountain ranges, river and lake systems and the like. Equally significant factors in the problem are climatic changes, which have had a profound and far-reaching effect upon the evolution and geographical spread of animals and plants, and the changes in the vegetable world must not be ignored, for, directly or indirectly, animals are dependent upon plants. To one who has paid no atten- tion to questions of this kind, it might well seem an utterly hope- less task to reconstruct the long vanished past, and he would naturally conclude that, at best, only fanciful speculations, with no foundation of real knowledge, could be within our reach. Happily, such is by no means the case. Geology offers the means of a successful attack upon these problems and, although very much remains to be done, much has already been accomplished in elucidating the history, especially in its later periods, with which the story of the mammals is more particularly concerned. It is manifestly impossible to present here a treatise upon the science of Geology, even in outline sketch. Considerations of space are sufficient to forbid any such attempt. Certain things must be taken for granted, the evidence for which may be found in any modern text-book of Geology. For example, 6 LAND MAMMALS IN THE WESTERN HEMISPHERE it is entirely feasible to establish the mode of formation of almost any rock (aside from certain problematical rocks, which do not enter into our discussion) and to determine whether it was laid down in the sea, or on the land, or in some body of water not directly connected with the sea, such as a lake or river. With the aid of the microscope, it is easy to discriminate volcanic material from the ordinary water-borne and wind- borne sediments and, in the case of the rocks which have solidified from the molten state, to distinguish those masses which have cooled upon the surface from those which have solidified deep within the earth. While the nature and mode of formation of the rocks may thus be postulated, it will be needful to explain at some length the character of the evidence from which the history of the earth may be deciphered. First of all, must be made clear the method by which the events of the earth’s history may be arranged inchronological order, for a history without chronology is unintelligible. The events which are most significant for our purpose are recorded in the rocks which are called stratified, bedded or sedimentary, synonymous terms. Such rocks were made mostly from the débris of older rocks, in the form of gravel, sand or mud, and were laid down under water, or, less extensively, spread by the action of the wind upon a land- surface. Important members of this group of rocks are those formed, more or less completely, from the finer fragments given out in volcanic eruptions, carried and sorted by the wind and finally deposited, it may be at great distances from their point of origin, upon a land-surface, or on the bottom of some body of water. Stratified or bedded rocks, as their name implies, are divided into more or less parallel layers or beds, which may be many feet or only a minute fraction of an inch in thickness. Such a division means a pause in the pro- cess of deposition or a change in the character of the material deposited over a given area. Owing to the operation of gravity, the layers of sediment are spread out in a horizontal METHODS — GEOLOGICAL 7 attitude, which disregard the minor irregularities of the bottom, just as a deep snow buries the objects which lie upon the surface. A moment’s consideration will show that, in any series of stratified rocks which have not been greatly disturbed from their original horizontal position, the order of succession or superposition of the beds must necessarily be the chronological order of their formation. (Fig. 1.) Obviously, the lowest beds must have been deposited first and therefore are the oldest of the series, while those at the top must be the newest or youngest and the beds intermediate in position are inter- mediate in age. This inference depends upon the simple prin- ciple that each bed must have been laid down before the next succeeding one can have been deposited upon it. While this is so clear as to be almost self-evident, it is plain that such a mode of determining the chronological order of the rocks of the earth’s crust can be of only local applicability and so far as the beds may be traced in unbroken continuity. It is of no direct assistance in correlating the events in the history of one continent with those of another and it fails even in com- paring the distinctly separated parts of the same continent. Some method of universal applicability must be devised before the histories of scattered regions can be combined to form a history of the earth. Such a universal method is to be found in the succession of the forms of life, so far as that is recorded in the shape of fossils, or the recognizable remains of animal and vegetable organisms preserved in the rocks. This principle was first enunciated by William Smith, an English engineer, near the close of the eighteenth century, who thus laid the foundations of Historical Geology. In the diagram, Fig. 2, is reproduced Smith’s section across England from Wales to near London, which shows the successive strata or beds, very much tilted from their original horizontal position by the upheaval of the sea-bed upon which they were laid down. The section pictures the side of an imaginary gigantic trench cut across the island and was constructed by a LAND MAMMALS IN THE WESTERN HEMISPHERE 3 o | 8 o Qo @ @ s $ 7 o| S| Sol § Bo] § g OS|uslwes| ab | OFS |mzl cE | F £ 9) os © o£ . & 3 &) Elda) § | £4!) §] 2 1% 3 5 a a ” 3 8 Yo o Q 3 ‘Sieh RS | my 2 J Lh 2 oO J ah 4 3 B | S om Ol ee Vt Ld $ eS iS oe a L ] oO YH faa) famst fue Woe eS s mn oO yy Ss La 36 fa feed fee oO LIL s | Q bal fe < a Hkh 8 3 Har 3 Lt ha 4 B o WH 2 fn mn m nL a Win s 3 Lt fu by HH 3 n Ht a 3 a =| = L} Ly a o L} by | Ro) fom = homed = Ly ty BH 3 m i o . ‘A baad Ly) je oe Lo a os bad fre SS | °o a 2 M4 ny = Lo tol bd mn ane H a ~~ —=—= & 8 eons rrr A | ] LI ai 3 Ly bog \ Ge METHODS — GEOLOGICAL 9 simple geometrical method from the surface exposures of the beds, such as mining engineers continually employ to map the underground extension of economically important rocks, and shows how an enormous thickness of strata may be studied from the surface. The older beds are exposed at the western end of the section in Wales and, passing eastward, successively later and later beds are encountered, the newest appearing at the easternend. Very many of the strata are richly fossiliferous, and thus a long succession of fossils was obtained in the order of their appearance, and this order has been found to hold good, not only in England, but throughout the world. The order Fic. 2.— William Smith’s section across the south of England. The vertical scale is exaggerated, which makes the inclination of the beds appear too steep. N.B. The original drawing is in colors, which are not indicated by the dotted strata. of succession of the fossils was thus in the first instance actually ascertained from the succession of the strata in which they are found and has been verified in innumerable sections in many lands and is thus a matter of observed and verifiable fact, not merely a postulate or working hypothesis. Once ascertained, however, the order of succession of living things upon the earth may be then employed as an independent and indispensable means of geologically dating the rocks in which they occur. This is the paleontological method, which finds analogies in many other branches of learned inquiry. The student of manuscripts discovers that there is a development, or regular series of successive changes, in handwriting, and from the hand- writing alone can make a very close approximation to the date of amanuscript. The order in which those changes came about 10 LAND MAMMALS IN THE WESTERN HEMISPHERE was ascertained from the comparative study of manuscripts, the date of which could be ascertained from other evidence, but, when once established, the changes in handwriting are used to fix the period of undated manuscripts. Just so, the succession of fossils, when learned from a series of superposed beds, may then be employed to fix the geological date of strata in another region. Similarly, the archeologist has observed that there is an evolution or development in every sort of the work of men’s hands and therefore makes use of coins, inscriptions, objects of art, building materials and methods, etc., to date ancient structures. In the German town of Trier (or Tréves) on the Moselle, the cathedral has as a nucleus a Roman structure, the date and purpose of which had long been matters of dispute, though the general belief was that the building had been erected under Constantine the Great. In the course of some repairs made not very long ago, it became necessary to cut deep into the Roman brickwork, and there, embedded in the undisturbed mortar, was a coin of the emperor Valentinian II, evidently dropped from the pocket of some Roman bricklayer. That coin fixed a date older than which the building cannot be, though it may be slightly later, and it well illustrates the service rendered by fossils in determining geo- logical chronology. Other methods of making out the chronology of the earth’s history have been proposed from time to time and all of them have their value, though none of them renders us independent of the use of fossils, which have the pre-eminent advantage of not recurring or repeating themselves at widely separated inter- vals of time, as all physical processes and changes do. An organism, animal or plant, that has become extinct never returns and is not reproduced in the evolutionary process. Great and well founded as is our confidence in fossils as fixing the geological date of the rocks in which they occur, it must not be forgotten that the succession of the different kinds of fossils in time was first determined from the superposition of METHODS — GEOLOGICAL 11 the containing strata. Hence, it is always a welcome con- firmation of the chronological inferences drawn from the study of fossils, when those inferences can be unequivocally estab- lished by the succession of the beds themselves. For example, in the Tertiary deposits of the West are two formations or groups of strata, called respectively the Uinta and the White River, which had never been known to occur in the same region and whose relative age therefore could not be determined by the method of superposition. Each of the formations, however, has yielded a large number of well-preserved fossil mammals, and the comparative study of these mammals made it clear that the Uinta must be older than the White River and that no very great lapse of time, geologically speaking, occurred between the end of the former and the beginning of the latter. Only two or three years ago an expedition from the American Museum of Natural History discovered a place in Wyoming where the White River beds lie directly upon those of the Uinta, thus fully confirming the inference as to the relative age of these two formations which had long ago been drawn from the comparative study of their fossil mammals. The paleontological method of determining the geological date of the stratified rocks is thus an indispensable means of correlating the scattered exposures of the strata in widely separated regions and in different continents, it may be with thousands of miles of intervening ocean. The general principle employed is that close similarity of fossils in the rocks of the regions compared points to an approximately contemporaneous date of formation of those rocks. This principle must not, however, be applied in an offhand or uncritical manner, or it will lead to serious error. In the first place, the evolutionary process is a very slow one and geological time is inconceivably long, so that deposits which differ by some thousands of years may yet have the same or nearly the same fossils. The method is not one of sufficient refinement to detect such relatively small differences. To recur to the illustration of the develop- LAND MAMMALS IN THE WESTERN HEMISPHERE 12 SHY A 9Y} Jo UoIsodep oy} 109Je Buoy] yNo podAred sea AaT]eA a ‘ g Cena THI YUL ‘Woy, usaajaq uoneredas ay} Suryreul oury uayouq ‘AAvey oy} ‘ezUI dy} JO sovjINS poroyzveM PUB UIOM ay} UO po}IsOdep a1aM spoq JOATY OY M OU ‘“BuIMOAM “OD quOMTeI ‘Ya0I9Q esa seh aie ee METHODS — GEOLOGICAL 13 ment in handwriting, the paleographer can hardly do more than determine the decade in which a manuscript was written ; no one would expect him to fix upon the exact year, still less the month, from the study of handwriting alone. As is the month in recorded human history, so is the millennium in the long course of the earth’s development. In the second place, there are great differences in the con- temporary life of separate regions and such geographical differ- ences there have always been, so far as we can trace back the history of animals and plants. A new organism does not originate simultaneously all over the world but, normally at least, in a single area and spreads from that centre until it encounters insuperable obstacles. Such spreading is a slow process and hence it is that new forms often appear in one re- gion much earlier than in others and in the very process of ex- tending their range, the advancing species may themselves be considerably modified and reach their new and distant homes as different species from those which originated the movement. Extinction, likewise, seldom occurs simultaneously over the range of a group, but now here and now there in a way that to our ignorance appears to be arbitrary and capricious. The process may go on until extinction is total, or may merely result in a great restriction of the range of a given group, or may break up that range into two or more distinct areas. Of such incomplete extinctions many instances might be given, but one must suffice. The camel-tribe, strange as it may appear, originated in North America and was long con- fined to that continent, while at the present day it is repre- sented only by the llamas of Seuth America and the true camels of Asia, having completely vanished from its early home. ‘These facts and a host of similar ones make plain how necessary it is to take geographical considerations into account in all problems that deal with the synchronizing of the rocks of separate areas and continents. Properly to estimate the significance of a difference in the 14 LAND MAMMALS IN THE WESTERN HEMISPHERE fossils of two regions and to determine how far it is geographical, due to a separation in space, or geological and caused by separa- tion in time, is often a very difficult matter and requires a vast amount of minute and detailed study. Once more, the princi- ple involved is illustrated by the study of manuscripts. Down to the time when the printing press superseded the copyist, each of the nations of Europe had its own traditions and its more or less independent course of handwriting development. A great monastery, in which the work of copying manuscripts went on century after century, became an independent geo- graphical centre with its particular styles. Thus the pale- ographer, like the geologist, is confronted by geographical prob- lems as well as by those of change and development in general. In addition to the method of geologically dating the rocks by means of the fossils which they contain, there are other ways which may give a greater precision to the result. Climatic changes, when demonstrable, are of this character, for they may speedily and simultaneously affect vast areas of the earth’s surface or even the entire world. From time to time in the past, glacial conditions have prevailed over immense regions, several continents at once, it may be, as in one instance in which India, South Africa, Australia, South America were involved. The characteristic accumulations made by the ,glaciers in these widely separated regions must be contempora- neous in a sense that can rarely be predicated of the ordinary stratified rocks. Such climatic changes as the formation and disappearance of the ice-fields give a sharper and more definite standard of time comparisons than do the fossils alone, and yet the fossils are in turn ‘needed to show which of several possible glacial periods are actually being compared. Again, great movements of the earth’s crust, which involve vast and widely separated regions and bring the sea in over great areas of land, or raise great areas into land, which had been submerged, may also yield more precise time-measure- ments, because occurring within shorter periods than do METHODS — GEOLOGICAL 15 notable changes in the system of living things. Such changes in animals and plants may be compared to the almost imper- ceptible movement of the hour-hand of a clock, while the re- corded climatic revolutions and crustal movements often supply the place of the minute-hand. It is obvious, however, that if the hour-hand be wanting, the minute-hand alone can be of very limited use. There have been a great many vast submer- gences and emergences of land in the history of the earth, and only the fossils can give us the assurance that we are comparing the same movement in distant continents, and not two similar movements separated by an enormous interval of time. It may thus fairly be admitted that it is possible to arrange the rocks which compose the accessible parts of the earth’s crust in chronological order and to correlate in one system the rocks of the various continents. The terms used for the more important divisions of geological time are, in descending order of magnitude, era, period, epoch, age or stage, and the general scheme of the eras and periods, which is in almost uniform use throughout the world, is given in the table, which is arranged so as to give the succession graphically, with the most ancient rocks at the bottom and-the, latest at the top. Quaternary period Tertiary period Cretaceous period Mesozoic era Jurassic period Triassic period Permian period Carboniferous period Devonian period Silurian period Ordovician period Cambrian period Cenozoic era Paleozoic era Algonkian period Pre-Cambrian eras Aroha Gere’ 16 LAND MAMMALS IN THE WESTERN HEMISPHERE It must not be supposed that all the divisions of similar rank, such as the eras, for example, were of equal length, as measured by the thickness of the rocks assigned to those divi- sions. On the contrary, they must have been of very unequal length and are of very different divisibility. The Pre-Cambrian eras, with only two periods, were probably far longer than all subsequent time, and all that the major divisions imply is that they represent changes in the system of life of approximately equivalent importance. It is impossible to give any trustworthy estimate of the actual lengths of these divisions in years, though many attempts to do so have been made. All that can be confidently affirmed is that geological time, like astronomical distances, is of in- conceivable vastness and its years can be counted only in hundreds of millions. To discuss in any intelligible manner the history of mammals, it will be necessary to go much farther than the above table in the subdivision of that part of geological time in which mammalian evolution ran its course. As mammals repre- sent the highest stage of development yet attained in the animal world, it is only the lattar part of the earth’s history which is concerned with them; the earlier and incomparably longer portion of that history may be passed over. Mammals are first recorded in the later Triassic, the first of the three periods which make up the Mesozoic era. They have also been found, though very scantily, in the other Mesozoic periods, the Jurassic and Cretaceous, but it was the Cenozoic era that witnessed most of the amazing course of mammalian develop- ment and diversification, and hence the relatively minute sub- divisions necessary for the understanding of this history deal only with the Cenozoic, the latest of the great eras. In the subjoined table the periods and epochs are those which are in general use throughout the world, the ages and stages are those which apply to the western interior of North America, each region, even of the same continent, requiring a METHODS — GEOLOGICAL 17 different classification. The South American formations are given in a separate table, as it is desirable to avoid the appear- ance of an exactitude in correlation which cannot yet be at- tained. CENOZOIC ERA Recent epoch Quaternary period } Pleistocene epoch = Glacial and Inter- glacial stages. Pliocene epoch Miocene epoch Tertiary period Oligocene epoch Eocene epoch Paleocene epoch Continuing the subdivision of the Tertiary period still farther, we have the following arrangement : TERTIARY PERIOD (North America) Upper Wanting Middle Blanco age Pliocene Thousand Creek age Lower | Snake Creek age Republican River age Upper Loup Fork age Miocene {Middle Deep River age Lower Arikaree age Upper John Day age Lower White River age Upper Uinta age Eocene Middle Bridger age Wind River age Wasatch age [Upper Torrejon age Lower Puerco age Oligocene Lower Paleocene | Fort Union Cc 18 LAND MAMMALS IN THE WESTERN HEMISPHERE This is arepresentative series of the wide-spread and manifold non-marine Tertiary deposits of the Great Plains, but a much more extensive and subdivided scheme would be needed to show with any degree of fullness the wonderfully complete record of that portion of the continent during the Tertiary period. A much more elaborate table will be found in Pro- fessor Osborn’s ‘“‘Age of Mammals,” p. 41. There are some differences of practice among geologists as to this scheme of classification, though the differences are not those of principle. No question arises concerning the reality of the divisions, or their order of succession in time, but merely as to the rank or relative importance which should be attributed to some of them, and that is a very minor consideration. Much greater difficulty and, eee much more radical differences of interpretation arise when the attempt is made to correlate or synchronize the smaller subdivisions, as found in the various continents, with one another, because of the geographical differences in contemporary life. Between Eu- rope and North America there has always been a certain pro- portion of mammalian forms in common, a proportion that was at one time greater, at another less, and this community renders the correlation of the larger divisions of the Tertiary in the two continents comparatively easy, and even in the minor subdivisions very satisfactory progress has been made, so that it is possible to trace in some detail the migrations of mammals from the eastern to the western hemisphere and vice versa. Such intermigrations were made possible by the land-bridges connecting America with Europe across the Atlantic, perhaps on the line of Greenland and Iceland, and with Asia where now is Bering Strait. These connections were repeatedly made and repeatedly broken during the Mesozoic and Cenozoic eras down to the latest epoch, the Pleistocene. By comparing the fossil mammals of Europe with those of North America for any particular division of geological time, METHODS — GEOLOGICAL 19 it is practicable to determine whether the way of intermigra- tion was open or closed, because separation always led to greater differences between the faunas of the two continents through divergent evolution. Correlation with South America is exceedingly difficult and it is in dealing with this problem that the widest differences of opinion have arisen among geologists. Through nearly all the earlier half of the Tertiary period the two Americas were separated and, because of this separation, their land mammals were utterly different. Hence, the lack of elements common to both continents puts great obstacles in the way of establish- ing definite time-relations between their geological divisions. Only the marine mammals, whales and dolphins, were so far alike as to offer some satisfactory basis of comparison. When, in the later Tertiary, a land-connection was established between the two continents, migrations of mammals from each to the other began, and thenceforward there were always certain elements common to both, as there are to-day. In spite of the continuous land between them, the present faunas of North and South America are very strikingly different, South America being, with the exception of Australia, zodlogically the most peculiar region of the earth. In the following table of the South pete Cenozoic, the assignment of the ages to their epochs is largely tentative, especially as regards the more ancient divisions, and repre- sents the views generally held by the geologists of Europe and the United States; those of South America, on the contrary, give an earlier date to the ages and stages and refer the older ones to the Cretaceous instead of the Tertiary. CENOZOIC ERA (South America) Recent epoch Quaternary period ; Pleistocene epoch —Pampean Beds, Brazilian caverns 20 LAND MAMMALS IN THE WESTERN HEMISPHERE Monte Hermoso age Pliocene epoch Catamarca age Parand age Santa Cruz age Patagonian age Deseado age (Pyrothe- Oligocene epoch rium Beds) Astraponotus Beds Casa Mayor age (Noto- stylops Beds) Tertiary period {Miocene epoch Eocene epoch The Pleistocene and Pliocene deposits are most widely dis- tributed over the Pampas of Argentina, but the former occur also in Ecuador, Brazil, Chili, and Bolivia. The other forma- tions cover extensive areas in Patagonia, and some extend into Tierra del Fuego. We have next to consider the methods by which past geo- graphical conditions may be ascertained, a task which, though beset with difficulties, is very far from being a hopeless under- taking. As has already been pointed out, it is perfectly possible for the geologist to determine the circumstances of formation of the various kinds of rocks, to distinguish terrestrial from aquatic accumulations and, among the latter, to identify those which were laid down in the sea and those which were formed in some other body of water. By platting on a map all the marine rocks of a given geological date, an approximate estimate may be formed as to the extension of the sea over the present land for that particular epoch. It is obvious, however, that for those areas which then were land and now are covered by the sea, no such direct evidence can be obtained, and only indirect means of ascertaining the former land-connections can be employed. It is in the treatment of this indirect evi- dence that the greatest differences of opinion arise and, if two maps of the same continent for the same epoch, by separate authors, be compared, it will be seen that the greatest dis- METHODS — GEOLOGICAL 21 crepancies between them are concerning former land-connec- tions and extensions. The only kind of indirect evidence bearing upon ancient land-connections, now broken by the sea, that need be con- sidered here is that derived from the study of animals and plants, both recent and fossil. All-important in this connection is the principle that the same or closely similar species do not arise independently in areas between which there is no con- nection. It is not impossible that such an independent origin of organisms which the naturalist would class as belonging to the same species may have occasionally taken place, but, if so, it must be the rare exception to the normal process. This principle leads necessarily to the conclusion that the more recently. and broadly two land-areas, now separated by the sea, have been connected, the more nearly alike will be their animals and plants. 'Such islands as Great Britain, Sumatra and Java must have been connected with the adjacent mainland within a geologically recent period, while the extreme zodlogical peculiarity of Australia can be explained only on the assumption that its present isolation is of very long standing.! The princi- ple applies to the case of fossils as well as to that of modern animals, and has already been made use of, in a preceding section, in dealing with the ancient land-connections of North America. It was there shown that the connection of this continent with the Old World and the interruptions of that connection are reflected and recorded in the greater or less degree of likeness in the fossil mammals at any particular epoch. Conversely, the very radical differences between the fossil mammals of the two Americas imply a long-continued separa- tion of those two continents, and their junction in the latter half of the Tertiary period is proved by the appearance of southern groups of mammals in the northern continent, and of northern groups in South America. Inasmuch as the connection between North and South America still persists, the geology of the Isthmus of Panama 22 LAND MAMMALS IN THE WESTERN HEMISPHERE should afford testimony in confirmation of the inferences drawn from a study of the mammals. Of course, the separating sea did not necessarily cross the site of the present isthmus.; it might have cut through some part of Central America, but a glance at the map immediately suggests the isthmus as the place of separation and subsequent connection. As a matter of fact, isthmian geology is in complete accord with the evidence derived from the mammals. Even near the summit of the hills which form the watershed between the Atlantic and the Pacific and through which the great Culebra Cut passes, are beds of marine Tertiary shells, showing that at that time the land was completely submerged. This does not at all preclude the possibility of other transverse seas at the same period ; indeed, much of Central America was probably under the sea also, but the geology of that region is still too imperfectly known to permit positive statements. When several different kinds of testimony, each inde- pendent of the other, can be secured and all are found to be in harmony, the strength of the conclusion is thereby greatly increased. Many distinct lines of evidence support the inference that North and South America were com- pletely severed for a great part of the Tertiary period. This is indicated in the clearest manner, not only by the geological structure of the Isthmus and by the mammals, living and extinct, as already described, but also by the fresh- water fishes, the land-shells, the reptiles and many other groups of animals and plants. The distribution of marine fossils may render the same sort of service in elucidating the history of the sea as land-mammals do for the continents, demonstrating the opening and closing of connections between land-areas and between oceans. The sea, it is true, is one and undivided, the continental masses being great islands in it, but, nevertheless, the sea is divisible into zodlogical provinces, just as is the land. Temperature, depth of water, character of the bottom, etc., are factors that METHODS — GEOLOGICAL 23 limit the range of marine organisms, as climate and physical barriers circumscribe the spread of terrestrial animals. Pro- fessor Perrin Smith has shown that in the Mesozoic era Bering Strait was repeatedly opened and closed, and that each opening and closing was indicated by the geographical relationships of the successive assemblages of marine animals that are found in the Mesozoic rocks of California and Nevada. When the Strait was open, the coast-line between North America and Asia was interrupted and the North Pacific was cooled by the influx of water from the Arctic Sea. At such times, sea-animals from the Russian and Siberian coasts extended their range along the American side as far south as Mexico, and no forms from the eastern and southern shores of Asia accompanied them. On the other hand, when the Strait was closed, the Arctic forms were shut out and the continuous coast-line and warmer water enabled the Japanese, Indian, and even Mediter- ranean animals to extend their range to the Pacific coast of North America. A comparison of the marine fishes of the two sides of the Isthmus of Panama shows an amount and degree of difference between the two series as might be expected from the length of time that they have been separated by the upheaval of the land. In working out the geographical conditions for any particular epoch of the earth’s history, it is possible to go much farther than merely gaining an approximate estimate of the distribu- tion of land and sea; many other important facts may be gathered from a minute examination of the rocks in combina- tion with a genetic study of topographical forms. By this physiographical method, as it is called, the history of several of the great mountain-ranges has been elaborated in great detail. It is quite practicable to give a geological date for the initial upheaval and to determine whether one or many such series of movements have been involved in bringing about the present state of things. Similarly, the history of plains and plateaus, hills and valleys, lake and river systems, may be ascertained, 24 LAND MAMMALS IN THE WESTERN HEMISPHERE and for the earth’s later ages, at least, a great deal may be learned regarding the successive forms of the land-surfaces in the various continents. It would be very desirable to ex- plain the methods by which these results are reached, but this could hardly be done without writing a treatise on physiog- raphy, for which there is no room in this chapter. We must be permitted to make use of the results of that science without being called upon to prove their accuracy. No factor has a more profound effect in determining the character and distribution of living things than climate, of which the most important elements, for our purpose, are temperature and moisture. One of the most surprising results of geological study is the clear proof that almost all parts of the earth have been subjected to great vicissitudes of climate, and a brief account of the evidence which has led to this un- looked for result will not be out of place here. The evidence of climatic changes is of two principal kinds, (1) that derived from a study of the rocks themselves, and (2) that given by the fossils of the various epochs. So far as the rocks laid down in the sea are concerned, little has yet been ascertained regarding the climatic conditions of their formation, but the strata which were deposited on the land, or in some body of water other than the sea, often give the most positive and significant information concerning the circumstances of climate which prevailed at the time of their formation. Cer- tain deposits, such as gypsum and rock-salt, are accumulated only in salt lakes, which, in turn, are demonstrative proof of an arid climate. A salt lake could not exist in a region of normal rainfall and, from the geographical distribution of such salt-lake deposits, it may be shown that arid conditions have prevailed in each of the continents and, not only once, but many times. As a rule, such aridity of climate was relatively local in extent, but sometimes it covered vast areas. For example, in the Permian, the last of the Palzozoic, and the Triassic, the first of the Mesozoic periods (see Table, p. 15) nearly all the METHODS — GEOLOGICAL 25 land-areas of the northern hemisphere were affected, either simultaneously or in rapid succession. Until a comparatively short time ago, it was very generally believed that the Glacial or Pleistocene epoch, which was so remarkable and conspicuous a feature of the Quaternary period, was an isolated phenomenon, unique in the entire history of the earth. Now, however, it has been conclusively shown that such epochs of cold have been recurrent and that no less than five of these have left unmistakable records in as many widely separated periods of time. When the hypothesis of a great ‘‘Ice Age”’ in the Pleistocene was first propounded by the elder Agassiz, it was naturally received with general incredulity, but the gradual accumula- tion of proofs has resulted in such an overwhelming weight of testimony, that the glacial hypothesis is now accepted as one of the commonplaces of Geology. The proofs consist chiefly in the characteristic glacial accumulations, moraines and drift- sheets, which cover such enormous areas in Europeand North America and, on a much smaller scale, in Patagonia, and in the equally characteristic marks of glacial wear left upon the rocks over which the ice-sheets moved. Many years later it was proved that the Permian period had been a time of gigantic glaciation, chiefly in the southern hemisphere, when vast ice-caps moved slowly over parts of South America, South Africa, Australia and even of India. The evidence is of precisely the same nature as in the case of the Pleistocene glaciation. In not less than three more ancient periods, the Devonian, Cambrian, and Algonkian, proofs of glacial action have been obtained. While the rocks themselves thus afford valuable testimony as to the climatic conditions which prevailed at the time and place of their formation, this testimony is fragmentary, missing for very long periods, and must be supplemented from the information presented by the fossils. As in all matters where fossils are involved, the evidence must be cautiously used, for 26 LAND MAMMALS IN THE WESTERN HEMISPHERE hasty inferences have often led to contradictory and absurd conclusions. When properly employed, the fossils give a more continuous and complete history of climatic changes than can, in the present state of knowledge, be drawn from a study of the rocks alone. For this purpose plants are particularly useful, because the great groups of the vegetable kingdom are more definitely restricted in their range by the conditions of temperature and moisture than are most of the correspondingly large groups of animals. Not that fossil animals are of no service in this connection; quite the contrary is true, but the evidence from them must be treated more carefully and criti- cally. To illustrate the use of fossils as recording climatic changes in the past, one or two examples may be given. In the Cretaceous period a mild and genial climate prevailed over all that portion of the earth whose history we ‘know, and was, no doubt, equally the case in the areas whose oalomy remains to be determined. The same conditions extended far into the Arctic regions, and abundant remains of a warm-temperate vegetation have been found in Greenland, Alaska and other Arctic lands. Where now only scanty and minute dwarf willows and birches can exist, was then a luxuri- ant forest growth comprising almost all of the familiar trees of our own latitudes, a most decisive proof that in the Cretaceous the climate of the Arctic regions must have been much warmer than at present and that there can have been no great accumu- lation of ice in the Polar seas. Conditions of similar mildness obtained through the earlier part of the Tertiary. In the Eocene epoch large palm-trees were growing in Wyoming and Idaho, while great crocodiles and other warm-country reptiles abounded in the waters of the same region. It is of particular interest to inquire how far the fossils of Glacial times confirm the inferences as to a great climatic change which are derived from a study of the rocks, for this may be taken as a test-case. Any marked discrepancy be- tween the two would necessarily cast grave doubt upon the METHODS — GEOLOGICAL 27 value of the testimony of fossils as to climatic conditions. The problem is one of great complexity, for the Pleistocene was not one long epoch of unbroken cold, but was made up of Glacial and Interglacial ages, alternations of colder and milder conditions, and some, at least, of the Interglacial ages had a climate warmer than that of modern times. Such great changes of temperature led to repeated migrations of the mammals, which were driven southward before the advancing ice-sheets and returned again when the glaciers withdrew under the influence of ameliorating climates. Any adequate discussion of these complex. conditions is quite out of the question in this place and the facts must be stated in simplified form, as dealing only with the times of lowered temperature and encroaching glaciers. The plants largely fail us here, for little is known of Glacial vegetation, but, on the other hand, a great abundance of the fossil remains of animal life of that date has been collected, and its testimony is quite in harmony with that afforded by the ice-markings and the ice-made deposits. Arctic shells in the marine deposits of England, the valley of the Ottawa River and of Lake Champlain, Walruses on the coast of New Jersey, Reindeer in the south of France, and Caribou in southern New England, Musk-oxen in Kentucky and Arkansas, are only a few examples of the copious evidence that the climate of the regions named in Glacial times was far colder than it is to-day. I have thus endeavored to sketch, necessarily in very meagre outlines, the nature of the methods employed to re- construct the past history of the various continents and the character of the evidence upon which we must depend. Should the reader be unconvinced and remain sceptical as to the possi- bility of any such reconstruction, he must be referred to the numerous manuals of Geology, in which these methods are set forth with a fulness which cannot be imitated within the limits of a single chapter. The methods are sound, consisting as they do merely in the application of “‘systematized common 28 LAND MAMMALS IN THE WESTERN HEMISPHERE sense”’ (in Huxley’s phrase) to observed facts, but by no means all applications of them are to be trusted. Not to mention ill-considered and uncritical work, or inverted pyramids of hypothesis balanced upon a tiny point of fact, it should be borne in mind that such a complicated and difficult problem as the reconstruction of past conditions can be solved only by successive approximations to the truth, each one partial and incomplete, but less so than the one which preceded it. CHAPTER II METHODS OF INVESTIGATION — PALHONTOLOGICAL PALZONTOLOGY is the science of ancient life, animal and vegetable, the Zodlogy and Botany of the past, and deals with fossils. Fossils are the recognizable remains or traces of animals or plants, which were buried in the rocks at the time of the formation of those rocks. In a geological sense, the term rock includes loose and uncompacted materials, such as sand and gravel, as well as solid stone. Granting the possibility of so determining the relative dates of formation of the rocks, that the order of succession of the fossils in time may be ascertained in general terms, the question remains: What use, other than geological, can be made of the fossils? In dealing with this question, attention will be directed almost exclusively to the mammals, the group with which this book is concerned. As a preliminary to the discussion, something should be said of the ways in which mammals became entombed in the rocks in which we find them. In this connection it should be remembered that, however firm and solid those rocks may be now, they were originally layers of loose and uncompacted material, deposited by wind or water, and that each layer formed in its turn the surface of the earth, until buried by fresh accumulations upon it, it may be to enormous depths. One method of the entombing of land-mammals, which has frequently been of great importance, is burial in volcanic dust and so-called ash, which has been compacted into firm rock. During a great volcanic eruption enormous quantities of such finely divided material are ejected from the crater and are spread out over the surrounding country, it may be for dis- 29 30 LAND MAMMALS IN THE WESTERN HEMISPHERE tances of hundreds of miles. Thus will be buried the scattered bones, skeletons, carcasses, that happen to be lying on the sur- face ; and if the fine fragments are falling rapidly, many animals will be buried alive and their skeletons preserved intact. A modern instance of this is given by the numerous skeletons of men and domestic animals buried in the volcanic ash which overwhelmed Pompeii in 79 a.p. Pliny the Younger, who witnessed that first recorded eruption of Vesuvius, tells us in a letter written to Tacitus, that far away at Misenum, west of Naples, it was often necessary to rise and shake off the falling ashes, for fear of being buried in them. In the Santa Cruz formation of Patagonia (see p. 124), which has yielded such a wonderful number and variety of well-preserved fossils, the bones are all found in volcanic dust and ash compacted into a rock, which is usually quite soft, but may become locally very hard. The Bridger formation of Wyoming (p. 110) and the John Day of eastern Oregon (p. 116) are principally made up of volcanic deposits ; and no doubt there are several others among the Tertiary stages which were formed in the same way, but have not yet received the microscopic study necessary to determine this. Much information concerning the mammalian life of the Pleistocene, more especially in Europe and in Brazil (p. 211), has been derived from the ‘exploration of caverns. Some of these caves were the dens of carnivorous beasts and contain multitudes of the bones of their victims, as well as those of the destroyers themselves. Others, such as the Port Ken- nedy Cave, on the Schuylkill River above Philadelphia, the Frankstown Cave in central Pennsylvania, the Conard Fissure in Arkansas, are hardly caverns in the ordinary sense of the word, but rather narrow fissures, into which bones and car- casses were washed by floods, or living animals fell from above and died without being able to escape. The bones are mostly buried in the earth which partially or completely fills many caverns and may be covered by a layer of stalagmite, derived METHODS — PALALONTOLOGICAL 31 from the solution and re-deposition of the limestone of the cavern-walls, by the agency of percolating waters. A mode of preservation which is unfortunately rare is ex- emplified by the asphaltic deposits near Los Angeles, at Rancho La Brea, which have been very fully described by Professor J. C. Merriam of the University of California. The asphalt has been formed by the oxidation and solidification of petro- leum, which has risen up through the Pleistocene rocks from the oil-bearing shales below. At one stage in the con- version of petroleum into asphalt, tar-pools of extremely viscid and adhesive character were, and still are, formed on the surface of the ground; and these pools were veritable traps for mam- mals and birds and for the beasts and birds of prey which came to devour the struggling victims. “The manner in which tar or asphalt pools may catch un- suspecting animals of all kinds is abundantly illustrated at the present time in many places in California, but nowhere more strikingly than at Rancho La Brea itself, where animals of many kinds have frequently been so firmly entrapped that they died before being discovered, or if found alive were extri- cated only with the greatest difficulty. As seen at this locality, the tar issuing from springs or seepages is an exceedingly sticky, tenacious substance which is removed only with the greatest difficulty from the body of any animal with which it may come in contact. Small mammals, birds, or insects running into the soft tar are very quickly rendered helpless by the gummy mass, which binds their feet, and in their struggles soon reaches every part of the body. Around the borders of the pools the tar slowly hardens by the evaporation of the lighter constituents until it becomes as solid as an asphalt pave- ment. Between the hard and soft portions of the mass there is a very indefinite boundary, the location of which can often be determined only by experiment, and large mammals in many cases run into very tenacious material in this intermediate zone, from which they are unable to extricate themselves.” 32 LAND MAMMALS IN THE WESTERN HEMISPHERE The foregoing account refers to what may actually be observed at the present time; in regard to the Pleistocene, Professor Merriam says: “In the natural accumulation of remains at the tar pools through accidental entangling of ani- mals of all kinds, it is to be presumed that a relatively large percentage of the individuals entombed would consist of young animals with insufficient experience to keep them away from the most dangerous places, or with insufficient strength to extricate themselves. There would also be a relatively large percentage of old, diseased, or maimed individuals that lacked strength to escape when once entangled. In the census of remains that have been obtained up to the present time the percentages of quite young, diseased, maimed, and very old individuals are certainly exceptionally large. ... In addi- tion to the natural accumulation of animal remains through the entangling of creatures of all kinds by accidental encoun- tering of the tar, it is apparent from a study of the collections obtained that some extraordinary influence must have brought carnivorous animals of all kinds into contact with the asphalt with relatively greater frequency than other kinds of animals. In all the collections that have been examined the number of carnivorous mammals and birds represented is much greater than that of the other groups. ... Whenever an animal of any kind is caught in the tar, its struggles and cries naturally attract the attention of carnivorous mammals and birds in the immediate vicinity, and the trapped creature acts as a most efficient lure to bring these predaceous animals into the soft tar with it. It is not improbable that a single small bird or mammal struggling in the tar might be the means of en- trapping several carnivores, which in turn would naturally serve to attract still others. ... In the first excavations carried on by the University of California a bed of bones was encountered in which the number of saber-tooth and wolf skulls together averaged twenty per cubic yard.” ! 1 Memoirs of the University of California, Vol. I, pp. 209-211. METHODS — PALZONTOLOGICAL 33 As the animals were thus entombed alive, it would be ex- pected that a large number of complete skeletons would be preserved, but this is not the case: ‘‘connected skeletons are not common.” This scattering and mingling of the bones were due partly to the trampling of the heavier animals in their struggles to escape, but, in more important degree, to the movements within the tar and asphalt. In arid and semi-arid regions great quantities of sand and dust are transported by the wind and deposited where the winds fail, or where vegetation entangles and holds the dust. Any bones, skeletons or carcasses which are lying on the surface will thus be buried, and even living animals may be suffocated and buried by the clouds of dust. An example of such wind-made accumulations is the Sheridan formation (Equus Beds, see p. 131), which covers vast areas of the Great Plains from Nebraska to Mexico and contains innumerable bones, especially of horses. In this formation in northwestern Kansas, Professor Williston found nine skeletons of the large peccary ({Platygonus leptorhinus), lying huddled together, with their heads all pointing in the same direction, and in the upper Miocene (p. 121) of South Dakota Mr. Gidley discovered six skeletons of three-toed horses ({Neohipparion whitneyt) crowded together, killed and buried probably by a sandstorm. Similar illustrations might be gathered from many other parts of the world. Swamps and bogs may, especially under certain conditions, become the burial places of great numbers of animals, which venture into them, become buried and are unable to extricate themselves. Especially is this true in times of great drought, when animals are not only crazed with thirst, but very much weakened as well, and so unable to climb out of the clinging mud. In an oft-quoted passage, Darwin gives a vivid description of the effects of a long drought in Argentina be- tween the years 1827 and 1830. ‘‘During this time so little D + Extinct. 34 LAND MAMMALS IN THE WESTERN HEMISPHERE rain fell, that the vegetation, even to the thistles, failed; the brooks were dried up, and the whole country assumed the appearance of a dusty high road.” ‘I was informed by an eyewitness that the cattle in herds of thousands rushed into the Parana, and being exhausted by hunger they were unable to crawl up the muddy banks, and thus were drowned. The arm of the river which runs by San Pedro was so full of putrid carcasses, that the master of a vessel told me that the smell rendered it quite impassable. Without doubt several hundred thousand animals thus perished in the river; their bodies when putrid were seen floating down the stream; and many in all probability were deposited in the estuary of the Plata. All the small rivers became highly saline, and this caused the death of vast numbers in particular spots; for when an animal drinks of such water it does not recover. Azara describes the fury of the wild horses on a similar occasion, rushing into the marshes, those which arrived first being overwhelmed and crushed by. those which followed. He adds that more than once he has seen the carcasses of upwards of a thousand wild horses thus destroyed. .. . Subsequently to the drought of 1827 to 1832, a very rainy season followed, which caused great floods. Hence it is almost certain that some thousands of the skeletons were buried by the deposits of the very next year.” ! In the arid and desolate regions of the interior of South Australia is a series of immense dry lakes, which only occasionally contain water and ordinarily ‘‘are shallow, mud-bottomed or salt-encrusted claypans only.” One of these, Lake Calla- bonna, is of great interest as having preserved in its soft mud many remains of ancient life, of creatures which were mired in the clay and destroyed, as has been described by Dr. E. C. Stirling. ‘There is, however, compensation for the unpromis- ing physical features of Lake Callabonna in the fact that its bed proves to be a veritable necropolis of gigantic extinct 1Voyage of a Naturalist, Amer. ed., pp. 133-134. METHODS — PALZONTOLOGICAL 35 marsupials and birds which have apparently died where they lie, literally, in hundreds. The facts that the bones of in- dividuals are often unbroken, close together, and, frequently, in their proper relative positions, the attitude of many of the bodies and the character of the matrix in which they are embedded, negative any theory that they have been carried thither by floods. The probability is, rather, that they met their deaths by being entombed in the effort to reach food or water, just as even now happens in dry seasons, to hundreds of cattle which, exhausted by thirst and starvation, are unable to extricate themselves from the boggy places that they have entered in pursuit either of water or of the little green herbage due to its presence. The accumulation of so many bodies in one locality points to the fact of their assemblage around one of the last remaining oases in the region of desiccation which succeeded an antecedent condition of plenteous rains and abundant waters.” It is a very general experience in collecting fossil mammals to find that they are not evenly or uniformly distributed through the beds, but rather occur in ‘“‘pockets,” where great numbers of individuals are crowded together, while between the “‘pockets”’ are long stretches of barren ground. It is equally common to find the bones thickly distributed in cer- tain layers, or beds, and the layers above and below entirely wanting in fossils. The reasons for this mode of occurrence have been partially explained in the foregoing paragraphs, but the reason differs for each particular mode of entombment. The important part played by drought in causing such ac- cumulation of closely crowded bodies in swamps and mud- holes is indicated in the quotations from Darwin and Stirling ; but similar accumulations may take place on hard ground, as was observed in central Africa by Gregory. ‘‘Here and there around a water hole we found acres of ground white with the bones of rhinoceroses and zebra, gazelle and ante- lope, jackal and hyena. ... These animals had crowded 36 LAND MAMMALS IN THE WESTERN HEMISPHERE around the dwindling pools and fought for the last drops of water.”’! Even in normal seasons springs and water holes and the drinking places in streams are the lurking places of beasts of prey and crocodiles, so that great accumula- tions of bones are made around these spots. A succession of unusually severe winters frequently leads to great mortality among mammals, as happened in Patagonia in the winter of 1899, when enormous .numbers of Guanaco perished of starvation on the shore of Lake Argentine, where they came to drink. Bones which are exposed on the surface of the ground decay and crumble to pieces in the course of a very few years; and if they are to be preserved as fossils, it is necessary that they should be buried under sedimentary or volcanic deposits. Several such modes of burial have been described in the fore- going paragraphs, but there are other and equally important methods, which remain to be considered. The deposits made by rivers are often extremely rich in fossils, and most of the Tertiary formations of the Great Plains are now ascribed to the agency of rivers. The flood-plain of a stream, or that part of its basin which is periodically over- flowed, is gradually built up by the layers of clay and silt thrown down by the relatively still waters of the flooded area, and scattered bones, skeletons or carcasses that may have been lying on the ground before the freshet are buried in the deposits. Bones covered up in this manner frequently show the marks of teeth of rodents or carnivores which have gnawed them when lying exposed. Deposits made in the stream- channels, where the current was swiftest, are of coarser materials such as gravel and sand, and these often contain the skeletons of animals which were drowned and swept downward by the flooded stream. When the Bison (the mistakenly so-called Buffalo) still roamed in countless herds over the western plains, immense numbers of them were drowned in the upper Missouri 1J. W. Gregory, The Great Rift Valley, p. 268. METHODS — PALHZONTOLOGICAL 37 River by breaking through the ice, when they attempted to cross at times when the ice had not attained its winter thickness, or was weakened by melting in the spring. No doubt, the bed of that river contains innumerable bones of the Bison. Fre- quently, too, animals are caught in quicksands and, unable to escape, are buried in the soft mass; fossil skeletons which are preserved in sandstones in an erect or standing position are usually to be interpreted in this manner. The sedimentary accumulations formed in lakes and ponds sometimes yield fossil bones or skeletons in considerable numbers, which have, for the most part, been derived from the carcasses of animals carried into the lake by streams. A newly drowned mammal sinks to the bottom and, if sufficient sediment be quickly deposited upon it, it may be anchored there and fossilized as a complete skeleton. Otherwise, when distended by the gases of putrefaction, the body will rise and float on the surface, where it will be attacked and pulled about by croco- diles, fishes and other predaceous creatures. As the bones are loosened in the course of decomposition, they will drop to the bottom and be scattered, now here, now there, over a wide area. Land mammals are rarely found in marine rocks, or such deposits as were made on the sea-bottom; but the remains of marine mammals, whales, porpoises, dolphins, seals, etc. are often found in large numbers. In principle, the method of entombment is the same as in the case of lakes, but currents may drift to some bay or cove multitudes of carcasses of these marine mammals. At Antwerp, in Belgium, incredible quanti- ties of such remains have been exposed in excavations and in all probability were drifted by currents into a quiet and shal- low bay, which was subsequently converted into land. While the foregoing account by no means exhausts the various methods of accumulation and burial of the skeletons and scattered bones of mammals, it covers the more important of these methods sufficiently for a general understanding of 38 LAND MAMMALS IN THE WESTERN HEMISPHERE the different processes. In whatever manner the preservation may have been effected, there is great difference in the rel- ative abundance and completeness among the fossils of the various kinds of mammals which were living at the same time and in the same area. It need hardly be said, that the more abundant any species was, the better was the chance of its being represented among the fossils; hence, gregarious species, living in large herds, were more likely to be preserved than those which led a solitary existence, or were individually rare. Most of the hoofed mammals are and apparently always have been gregarious, and are therefore much better represented among the fossils, and are, in consequence, better known than the beasts of prey, which, of necessity, were individually less numerous and. generally solitary in habits. Not only this, but large and medium-sized mammals, with strong and heavy bones, were better fitted to withstand the accidents of entomb- ment and subsequent preservation than small creatures with delicate and fragile skeletons. The mere dead weight of over- lying sediments often crushes and distorts the bones, and the movements of uplift, compression, folding and fracture, to which so many strata have been subjected, did still further damage to the fossils. The percolating waters, which for ages have traversed the porous rocks, often attack and dissolve the bones, completely destroying the minute ones and greatly injuring those which are massive and. strong. In consequence of all those accidents it frequently happens that only the teeth, the hardest and most resistant of animal structures, and it may be the dense and solid jaw-bones, are all that remain to testify of the former existence of some creature that long ago vanished from the earth. Very many fossil mammals are known exclusively from the teeth, and it is this fact which makes the exact study of teeth so peculiarly important to the pale- ontologist. In view of all these facts, it is not surprising that con- cerning the history of many mammalian groups we have but METHODS — PALHZONTOLOGICAL 39 scanty information, or none at all, while in the case of others the story is wonderfully full and detailed. The latter are, very generally, the groups which were not only numerically abundant at: all stages of their history, but also had skeletons that were strong enough to resist destruction; while the. groups as to which there is little or no information are chiefly of small and fragile animals, or such as were always rare. For example, a great deal has been learned regarding the de- velopment of horses and rhinoceroses in North America, but the history of the tapirs is very unsatisfactorily known, be- cause, while horses and rhinoceroses were common, tapirs were solitary and rare. In Europe bats have been found in the Eocene, Oligocene and Miocene, and there is no reason to suppose that they were not equally ancient and equally abundant in America; but none have been found in the western hemisphere in any formation older than the Pleistocene. All things considered, the extraordinary fact is, not that so many forms have irretrievably perished, but that so much has been preserved, escaping all the chances of destruction. As to the degree of preservation in fossil mammals, we have to do almost entirely with bones and teeth. With very rare exceptions, and those all of late geological date, the viscera, muscles, skin, hair, horns, hoofs and claws have been com- pletely destroyed and have vanished without leaving a trace. In northern Siberia the gravel soil is permanently frozen to a depth of several hundred feet and contains the intact carcasses of elephants and rhinoceroses of Pleistocene date and notably different from any species of these animals now in existence. Sometimes such a carcass is disinterred from a bluff by the cutting action of a stream and is in a state of nearly complete preservation, with hide, hair and flesh almost as in an animal freshly killed. From these remains it has been learned that the {Mammoth was an elephant densely covered with hair and wool, just as he was depicted in the carvings and cave-paintings t Extinct. 40 LAND MAMMALS IN THE WESTERN HEMISPHERE of Pleistocene Man in Europe, where {Mammoth bones have been abundantly found, and also that there were Siberian rhinoceroses similarly protected against the cold. tMammoth remains with hide and flesh, but much less complete, have like- wise been found in Alaska. In a cavern in southern Patagonia an expedition from the La Plata Museum discovered, with the remains of a gigantic, extinct tground-sloth, large pieces of the skin still covered with hair and affording most welcome information as to the colouration of these most curious animals. The skin had been preserved from decay by deep burial in dry dust. Mummies of Pleistocene rodents have been found in the dry caves of Portugal, whereas in the ordinary caves which are damp or wet, only bones are preserved. Unfortunately, as has been said, such instances of complete preservation are very rare, and none are known of mammals more ancient than those of the Pleistocene epoch. In general, it may be said that the higher the geological antiquity of a skeleton is, the greater is the chemical alteration which it has undergone. Bones of Pleistocene or later date have, as a rule, suffered little change beyond the loss of more or less of their animal matter, the amount of such loss depending chiefly upon exposure to the air. Bones which, for thousands or tens of thousands of years, have been buried in dense cave- earth, in an antiseptic peat-bog, or in asphalt, are often per- fectly sound and fresh when taken up. Skeletons of the ante- cedent (Tertiary) period are, on the other hand, very frequently petrified; that is to say, the original substance of the bones has been completely removed and replaced by some stony material, most commonly lime or flint. This substitution took place very gradually, molecule by molecule, so that not only is the form of the bone or tooth most accurately reproduced, but the internal, microscopic structure is perfectly retained and may be studied to as great advantage as in the case of modern animals. t Extinct. METHODS — PALZONTOLOGICAL 41 While, save in the rarest instances, only the hard parts of fossil mammals remain to testify of their structure, very im- portant information as to the size, form and external character of the brain may be secured from ‘‘brain-casts,’”’ which may be natural or artificial, The pressure of the mud, sand or other material, in which the fossil was embedded, filled up all openings in the skeleton and, as the brain decayed and dis- appeared, its place was taken by this material, which subse- quently hardened and solidified and quite accurately reproduces the external form and character of the brain. When a fossil skull is exposed and shattered by weathering, the natural brain-cast often remains intact, and a great many such speci- mens are in the collections. An artificial cast is made by saw- ing open the cranial cavity, cleaning out the stony matrix , which fills it and then pouring liquid gelatine or plaster of Paris into the cavity. These artificial casts are often quite as satisfactory as the natural ones. As has been shown above, the history of the mammals is recorded, save.in a very few instances, in terms of bones and teeth and, to the uninitiated, it might well seem that little could be accomplished with such materials. However, it is the task, and the perfectly feasible task, of paleontology to make these dry bones live. It is a current and exceedingly mischievous notion that the paleontologist can reconstruct a vanished animal from a single bone or tooth and, in spite of repeated slayings, this delusion still flourishes and meets one in modern literature at every turn. No doubt, much of the scepticism with which attempts to restore extinct animals are met by many intelligent people is traceable to the wide- spread belief that such off-hand and easy-going methods are used in the work. So far from being able to make a trust- worthy reconstruction from a few scattered bones, competent palzontologists have been sometimes led completely astray in associating the separated parts of the same skeleton. More than once it has happened that the dissociated skull and feet 42 LAND MAMMALS IN THE WESTERN HEMISPHERE of one and the same animal have been assigned to entirely different groups, just because no one could have ventured, in advance of experience, to suppose that such a skull and teeth could belong to a creature with such feet. In all these cases (and they are few) the error has been finally corrected by the discovery of the skeleton with all its essential parts in their natural connection. While the number of complete skeletons of Tertiary mam- mals as yet collected is comparatively small, it is often possible to construct a nearly complete specimen from several imperfect ones, all of which can be positively shown to belong to the same species. Such composite skeletons are almost as useful as those in which all the parts pertain to a single individual, though in making the drawings it is not easy to avoid slight errors of proportion. It must not be supposed that no success- ful restoration of missing bones is practicable ; on the contrary, this can often be done very easily, but only when all the essential parts of the skeleton are known. Even if an unlimited number of perfect skeletons were available, of what use would they be? A skeleton is a very different looking object from a living animal, and how is it possible to infer the latter from the former? Do the many restorations of extinct mammals which this book owes to the skill of Mr. Horsfall and Mr. Knight deserve any other con- sideration than that due to pleasing, graceful or grotesque fancies, with no foundation of solid fact? 'To answer these questions, it is necessary first to consider the relations of the bony structure to the entire organism and then to discuss the principles in accordance with which the restorations have been made. The skeleton is far from being merely the mechanical frame- work of the animal. Such a frame-work it is, of course, but it is much more than that ; it is the living and growing expres- sion of the entire organism and is modified, not only by age, but by the conditions of the environment and accidental cir- METHODS — PALZONTOLOGICAL 43 cumstances as well. The bones of the same individual differ very materially in early youth, maturity and old age; so long as the animal lives, its bones are perpetually changing, slowly it is true, but with ready response to needs. Not only that, but dislocated bones may and frequently do develop entirely new joints, and their internal structure is remodelled to meet the requirements of stresses differing in character or direction from those of normal, uninjured bones. The general form and proportions of any.mammal are determined chiefly by its muscular system and this may be directly and confidently inferred from its skeleton, for the muscles which are of im- portance in this connection are attached to the bones and leave their indelible and unmistakable mark upon them. In any good text-book of anatomy this extremely intimate relation of bone and muscle is made clear; and it is shown how each attachment of muscle, tendon and ligament is plainly indicated by rough lines, ridges, projections or depressions, which speak a language intelligible enough to those who have learned to interpret it. Given the skeleton, it is no very difficult task to reconstruct the muscular system in sufficient detail. Further, the teeth afford valuable information as to the food, habits and appearance of the animal, for the bulk of the viscera, a significant element in the general form, is principally con- ditioned by the character of the diet. Beasts of prey, which live by catching and devouring other animals, have a certain likeness to one another, even though they are in no wise related, except as all mammals are. The Thylacine, or so-called “Tasmanian Wolf” (Thylacynus cynocephalus), a marsupial and related to the opossums, is deceptively like the true wolves in appearance, although be- longing to an order (Marsupialia) almost as widely separated from that to which the wolves belong (Carnivora) as two mammalian groups well can be. This resemblance is as clearly indicated by the skeletons as by the living animals themselves, though the fundamental. differences of structure which dis- 44 LAND MAMMALS IN THE WESTERN HEMISPHERE tinguish the marsupial from the carnivore are no less clearly displayed. Large herbivorous mammals too, though referable to very different orders, bear a strong resemblance to one another, the characteristic differences, so far as the living animal is concerned, appearing chiefly in the head. It was this general likeness that induced Cuvier to form his order, ‘‘Pachyder- mata,” which comprised elephants, rhinoceroses, hippopota- muses, tapirs, etc., animals that are now distributed into no less than three separate orders; aside from the head, all of these forms are quite distinctly similar in appearance. Of course, the external features, such as ears, tail, skin and hair, are most important factors in the general make-up of any mammal; and, as to these matters, the fossils leave us largely in the lurch, save in the all too rare cases, like the Si- berian {Mammoth, in which these external features are actually preserved. Two artists may so restore the same animal as to result in two very different pictures, and no one can posi- tively decide between them; just as two modern mammals, which are closely related and have very similar skeletons, may yet differ markedly in outward appearance, because of the different character of the skin, as do, for example, the Bornean and Indian rhinoceroses. Yet even in dealing with purely external features, we are not left altogether to conjecture. Ears of unusual size or form frequently leave some indication of this on the skull, and the presence or absence of a proboscis can nearly always be inferred with confidence from the char- acter of the bones of the nose and muzzle. The length and thickness of the tail may be generally directly deduced from the caudal vertebre, but whether it was close-haired and cylindrical, or bushy, or tufted at the end, or flat and trowel- shaped, as in the Beaver, is not determinable from the bones alone. Most uncertain of all the characters which determine outward appearance are the hair and the pattern of colouration ; the Horse and Zebra differ much more decidedly in the living METHODS — PALZONTOLOGICAL 45 form than their skeletons would lead one to expect, as do also the Lion, the Tiger and the Leopard. The curious and ex- ceptional colour-pattern of the Okapi, that remarkable giraffe- like animal but lately discovered in the equatorial forests of western Africa, could never have been inferred from a study of the skeleton alone. However, even in the problem of colour- patterns there is more to go upon than sheer guess-work, for certain definite principles of animal colouration have been ascertained ; the great difficulty lies in the application of these principles to a particular case. It is quite certain that the naked, hairless skin is never primitive, but always a compara- tively late acquisition and, in many mammalian orders, is not found at all. Aside from a few domesticated animals, this type of skin occurs only in very large herbivorous mammals living in warm climates, such as elephants, rhinoceroses and hippopotamuses, in a few burrowers, and in marine mammals, like the walruses, whales, porpoises, etc. Useful hints as to the colouring of ancient and extinct forms may be gathered from <= TF BRUCE HORSPALL ims) at ——" Fic. 4. — Wild sow and pigs, showing the uniform colour of the adult and stripes of the young. 46 LAND MAMMALS IN THE WESTERN HEMISPHERE a study of series of living animals, such as lizards and butter- flies, in which the development of a definite scheme of coloura- tion may be followed step by step. Young animals very fre- quently retain more or less distinct traces of the ancestral colouration, which disappear in the adult, for the develop- ment of the individual is, in some respects at least, an abbre- viated and condensed recapitulation of the history of the species. In many mammals which, in the adult condition, have a solid body-colour, the young are striped or spotted, a strong indi- cation that these mammals were derived from striped or spotted ancestors. Thus, the Wild Boar has a uniform body-colour in the full-grown stage, but the pigs are longitudinally striped ; many deer are spotted throughout life, as in the Fallow Deer, the Axis Deer of India and others, but the great majority of the species, including all the American forms, have uniform colouration, while the fawns are always spotted. Lion cubs Fic. 5.— Fawns of the Mule Deer (Odocoileus hemionus). Compare with Fig. 83, p. 167. (By permission of the N. Y. Zodlog. Society.) are also spotted and the adults have a uniform tawny colour, and many such examples might be given. The study of colouration among existing animals has led to the conclusion that in mammals the primitive colour- METHODS — PALZONTOLOGICAL 47 pattern was that of stripes, either longitudinal or transverse and more probably the former. In the second stage these bands break up into spots, which still show the longitudinal arrangement and may be either light on a dark ground, or dark on a light ground. In a third stage the spots may again coalesce into stripes, the course of which is at right angles to that of the original stripes, or the spots may disappear, leaving a uniform body-colour, lighter or white on the belly. These changes of colour-pattern have. not proceeded at a uniform rate in the various mammalian groups, or even within the same group, for an all-important factor is the mode of life of the particular animal. In general, it may be said that the scheme of colour is such as to render its possessor inconspicuous, or even invisible, and many a creature that seems to be very conspicuous and striking in a museum case can hardly be seen at all when in its natu- ral surroundings. Thus, Arctic mammals and birds, in their yy¢. ¢.—rapirus terrestris, 3 days old. winter dress, are white ; desert Compare with Fig. 137, p. 320. (By 5 permission of W.S. Berridge, London.) animals are tawny or sandy- brown ; forest animals are frequently striped or spotted ; while those that live on open plains are more commonly of uniform colouration. There are exceptions to these rules, but they hold good for the most part. From careful comparative study of the teeth and skeletons a clew may be gained as to the habits of animals and from the habits something may be inferred as to the colouration. It would, however, be misleading to claim a greater au- thority for these attempts at restoring a long-vanished life than can fairly be ascribed to them. The general form and proportions of the head, neck, body, tail, limbs and feet may be deduced with a high degree of accuracy from the skeleton, 48 LAND MAMMALS IN THE WESTERN HEMISPHERE while the external characters of skin, hair and colouration are largely conjectural, but not altogether imaginary. It cannot be doubted that among the extinct mammals were many which, owing to some uncommon growth of subcutaneous fat, or some unusual local development of hair, were much more curious and bizarre in appearance than we can venture to represent them. If, for example, the Camel, the Horse, the Lion and the Right Whale were extinct and known only from their skeletons, such restorations as we could make of them would assuredly go astray in some particulars. The Camel would be pictured without his hump, for there is nothing in the skeleton to suggest it; the forelock, mane and characteristic tail of the Horse and the Lion’s mane would certainly not be recognized ; while the immense development of blubber in the head of the Whale gives to it a very different appearance from that which the skull would seem to indicate. Such cases are, however, ex- ceptional and restorations made by competent hands from complete skeletons probably give a fair notion of the appearance of those animals when alive. It will thus be sufficiently plain that the work of restora- tion is beset with difficulties, but that there is no good ground for the uncritical scepticism which summarily rejects the re- sults as being purely fanciful, or for the equally uncritical credulity which unhesitatingly accepts them as fully and in- contestably accurate. It is altogether likely that one of the main sources of error consists in making the extinct animal too closely resemble some existing species which is selected as a model. Too much space has perhaps been devoted to the problem of restoring the external form of these extinct mammals, a problem which, after all, is of distinctly subordinate impor- tance. The most valuable results which may be gained from a study of these fossil mammals are the answers which they afford to the great questions of relationship, classification and genetic descent, and the light which they throw upon the METHODS — PALZONTOLOGICAL 49 processes of evolution and the course of geographical arrange- ment. The bones and teeth afford admirable means of tracing the gradual steps of modification by which the modern mammals have arisen from very different ancestors and of following their wanderings from region to region and continent to continent. It is to these questions that most of the subse- quent chapters are devoted. CHAPTER III THE CLASSIFICATION OF THE MAMMALIA THE terminology and nomenclature of science form a great barrier, which only too often shuts out the educated layman from following the course of investigation and keeping abreast of the discoveries in which he may be particularly interested. No more frequent and heartfelt complaint is uttered than that which decries the ‘‘scientific jargon,’ and one might be tempted to think that this jargon was a superfluous nuisance, delib- erately adopted to exclude the uninitiated and guard the secrets of the temple from the curious intruder. As a matter of fact, however, this terminology, though an unquestionable evil from one point of view, is an indispensable implement of investigation and description. Ordinary language has far too few words for the purpose and most of the words that might be used lack the all-important quality of precision. The vernacular names of animals and plants are notoriously inexact and, even when not inaccurately employed, are not sufficiently refined and destinctive for scientific use. This is pre-eminently true of the New World, where the European settlers gave the names of the creatures with which they had been familiar at home to the new animals which they found in the western hemisphere. Some of these names, such as deer, wolf, fox, bear, are accurate enough for ordinary purposes, while others are ludicrously wrong. The bird that we call the Robin is altogether different from his European namesake, and the great stag, or Wapiti, is commonly called ‘‘Elk,” a name which properly belongs to the Moose. In short, it is impossible to gain the necessary accuracy and abundance of vocabulary 50 CLASSIFICATION OF THE MAMMALIA 51 without devising an artificial terminology, drawn chiefly from Greek and Latin. In dealing with fossils, the difficulty of nomenclature be- comes formidable indeed. ‘The larger and more conspicuous mammals of the modern world are more or less familiar to all educated people, and such names as rhinoceros, hippopotamus, elephant, kangaroo, will call up a definite and fairly accurate image of the animal in question. For the strange creatures that vanished from the earth ages before the appearance of Man there are no vernacular names and it serves no good pur- pose to coin such terms. To the layman names like Uinta- therium or Smilodon convey no idea whatever, and all that can be done is to attempt to give them a meaning by illustration and description, using the name merely as a peg upon which to hang the description. The system of zodlogical classification which is still in use was largely the invention of the Swedish naturalist Linneus, who published it shortly. after the middle of the eighteenth century. As devised by Linnzus, the scheme was intended to express ideal relationships, whereas now it is employed to express real genetic affinities, so far as these can be ascertained. The Linnzan system is an organized hierarchy of groups, arranged in ascending order of comprehensiveness. In this scheme, what may be regarded as the unit is the species, a concept around which many battles have been waged and concerning which there is still much difference of opinion and usage. Originally a term in logic, it first received a definite meaning in Zodlogy and Botany from John Ray (1628-1705) who applied it to indicate a’group of animals, or plants, with marked common characters and freely interbreeding. Linnzus, though not always consistent in his expressions on the subject, regarded species as objective realities, concrete and actual things, which it was the naturalist’s business to discover and name, and held that they were fixed entities which had been separately created. This belief in the fixity and objective 52 LAND MAMMALS IN THE WESTERN HEMISPHERE reality of species was almost universally held, until the publica- tion of Darwin’s ‘‘Origin of Species’ (1859) converted the biological world to the evolutionary faith, which declares that the only objective reality among living things is the individual animal or plant. According to this modern conception, a species may be defined as signifying a ‘‘ grade or rank assigned by systematists to an assemblage of organic forms which they judge to be more closely interrelated by common descent than they are related to forms judged to be outside the species ’’ (P. Chalmers Mitchell). The technical name of a species, which is either in Latin, or in latinized form, is in two words, one of which designates the genus (see below) and the other the particular species of that genus, as, for example, Equus caballus, the species Horse, EF. przewalskii, the Asiatic Wild Horse, H. asinus, the species Ass, etc. In order to identify a species, the genus to which it belongs must be stated, hence the term, binomial system of nomenclature, which Linneus introduced, becoming ¢ri- nomial when the name of a subspecies is added, a modern re- finement on the older method. A very large species (7.e. one which is represented by great numbers of individuals), extending over a very large area, is often divisible into groups of minor rank, as varieties, geographical races or subspecies. Taking the species as the unit in the scheme of classification, the varieties and subspecies may be considered as fractions. There is great difference of usage among writers on sys- tematic zodlogy in the manner of applying the generally ac- cepted concept of species, some making their groups very much more comprehensive than others, according as they are “‘lumpers”’ or ‘‘splitters,” to employ the slang phrase. The difficulty lies in the fact that there are no fixed and definite criteria, by which a given series of individuals can be surely distinguished as a variety, a species or a genus; it is a matter for the judgment and experience of the systematist himself. The individuals of a species may differ quite widely among CLASSIFICATION OF THE MAMMALIA 53 themselves, provided that they are all connected by inter- gradations, and the more or less constant varieties or sub- species are to be distinguished from the individual variants, which are inconstant and fluctuating. No two specimens agree exactly in every particular, but if a very large suite of them be compared, it will be found that the great majority depart but little from the average or norm of the species, and the wider the departure from the norm, the fewer the indi- viduals which are so aberrant. Taking so easily measured a character as size, for example, and measuring several hundred or a thousand representatives of some species, we see that a large majority are of average size, a little more or a little less, while very large or very small individuals are rare in propor- tion to the amount by which they exceed or fall short of the norm. Subspecies or varieties are marked by differences which are relatively constant, but not of sufficient importance to entitle them to rank as species. A group of the second rank is called a genus, which may contain few or many species, or only asingle one. In the latter case the species is so isolated in character that it cannot prop- erly be included in the same genus with any other species. A large genus, one containing numerous species, is frequently divisible into several subgenera, each comprising a group of species which are more similar to one another than they are to the other species of the genus. The third of the main groups in ascending order is the family, which ordinarily consists of a number of genera united by the possession of certain common characters, which, at the same time, distinguish them from other genera, though a single isolated genus may require a separate family for its reception. Just as it is often convenient to divide a genus into subgenera, so families containing many genera are usually divisible into subfamilies, as indicative of closer relationships within the family. The name of the family is formed from that of the genus first described or best known, with the 54 LAND MAMMALS IN THE WESTERN HEMISPHERE termination -ide, while that for the subfamily is ne. To take an example, all the genera of cats, living and extinct, are assembled in the family Felide (from the genus Felis) which falls naturally into two subfamilies. One of these, the Feline, includes the true cats, a very homogeneous group, both the existing and the extinct genera; the other subfamily, that of the highly interesting series of the ‘‘Sabre-tooth Tigers,” called the {Machairodontine, comprises only extinct forms. The fourth principal rank or grade is the order, distin- guished by some fundamental peculiarity of structure and usually including a large number of families. Some of the orders, however, contain but a single family, a single genus, or even, it may be, a single species, because that species is in important structural characters so unlike any other that it cannot properly be put into the same order with anything else. Such isolation invariably implies that the species or genus in question is the sole survivor of what was once an extensive series. As in the case of the family and the genus, it is often necessary: to recognize the degrees of closer and more remote affinity by the use of suborders. Existing Artiodactyla, or even-toed hoofed animals, an enormous assemblage, may con- veniently be divided into four suborders: (1) Suina, swine and the Hippopotamus; (2) Tylopoda, the ‘Camel and Llama; (3) Tragulina, ‘‘mouse-deer,’”’ or chevrotains; (4) Pecora, or true ruminants, deer, giraffes, antelopes, sheep, goats, oxen, etc. In nearly all of the orders such subordinal divisions are desirable and it is frequently useful to employ still further subdivisions, like superfamilies, which are groups of allied families within the suborder, sections and the like. In the Linnzan scheme, the next group in ascending rank is the class, which includes all mammals whatsoever, but the advance of knowledge has made it necessary to interpolate several intermediate grades between the class and the order, which, in the descending scale, are subclass, infraclass, cohort, + Extinct. CLASSIFICATION OF THE MAMMALIA 55 superorder and others, while above the class comes the sub- kingdom of Vertebrata, or animals with internal skeletons, which includes mammals, birds, reptiles, amphibians and fishes. A word should be said as to the conventions of printing technical names. The names of all species are, in American practice, printed in small letters, but many Europeans write specific terms which are proper nouns or adjectives with a capital. Generic, family and all groups of higher rank are always written with a capital, unless used in vernacular form, e.g. Artiodactyla and artiodactyls. It is also a very general custom to give capitals to vernacular names of species, as the Mammoth, the Coyote, the Black Bear. Genus and species are almost invariably in italics, groups of higher rank in roman. Such a scheme of classification as is outlined above has a decidedly artificial air about it and yet it serves a highly use- ful purpose in enabling us to express in brief and condensed form what is known or surmised as to the mutual relationships of the great and diversified assemblage of mammals. The scheme has been compared to the organization of an army into company, battalion, regiment, brigade, division, army corps, etc., and there is a certain obvious likeness ; but the differences go deeper, for an army is an assemblage of similar units, mechanically grouped into bodies of equal size. A much closer analogy is the genealogical or family tree, which graphically expresses the relationships and ramifications of an ancient and wide-spread family, though even this analogy may easily be pushed too far. Blood-relationship is, in short, the under- lying principle of all schemes of classification which postulate the theory of evolution. The system of Linnzus, as expanded and improved by modern zodlogists, has proved itself to be admirably adapted to the study of the living world ; but it is much more difficult to apply it to the fossils, for they introduce a third dimension, so to speak, for which the system was not designed. This 56 LAND MAMMALS IN THE WESTERN HEMISPHERE third dimension is the successive modification in time of a genetically connected series. The cumulative effect of such modifications is so great that only very elastic definitions will include the earlier and later members of an unbroken series. In attempting to apply the Linnean system to the successive faunas (i.e. assemblages of animals) which have inhabited the earth, paleontologists have employed various devices. One such method is to classify each fauna without reference to those which precede and follow it, but this has the great draw- back of obscuring and ignoring the relationships, to express which is the very object of classification. Another and more logical method is to treat species and genera as though they belonged to the present order of things, for these groups, particularly species, were relatively short-lived, when regarded from the standpoint of geological time, and either became so modified as to require recognition as new species and genera, or died out without leaving descendants. Groups of higher rank, families, orders, etc., are treated as genetic series and include the principal line or stock and such side-branches as did not ramify too widely or depart too far from the main stem. Under the first arrangement, the horses, a long history of which has been deciphered, would be divided into several families ; under the second, they are all included in a single family. One of the most interesting results of palzontological study is the discovery that in many families, such as the horses, rhinoceroses and camels, there are distinct series which in- dependently passed through parallel courses of development, the series of each family keeping a remarkably even pace in the degree of progressive modification. Such a minor genetic series within a family is called a phylum, not a very happy selection, for the same term had been previously employed in a much wider sense, as equivalent to the subkingdom. In both uses of the term the underlying principle, that of genetic series, is the same ; the difference is in the comprehensiveness of meaning. CLASSIFICATION OF THE MAMMALIA 57 It must be admitted that no method, yet devised, of apply- ing the Linnzan scheme to the fossils is altogether satisfactory, and indeed it is only the breaks and gaps in the paleontological record which makes possible any use of the scheme. Could we obtain approximately complete series of all the animals that have ever lived upon the earth, it would be necessary to invent some entirely new scheme of classification in order to express their mutual relationships. In the present state of knowledge, classification can be made only in a preliminary and tentative sort of way and no doubt differs widely from that which will eventually be reached. So far as the mammals are concerned, part of the problem would seem to be quite easy and part altogether uncertain. Some mammalian groups appear to be well defined and entirely natural assemblages of related forms, while others are plainly heterogeneous and artificial, yet there is no better way of dealing with them until their history has been ascertained. The mutual relations of the grand groups, or orders, are still very largely obscure. The class Mammalia is first of all divided into two sub- classes of very unequal size. Of these, the first, PROTO- THERIA, is represented in the modern world by few forms, the so-called Duck-billed Mole (Ornithorhynchus paradoxus) and Spiny Anteaters (Echidna) of Australia. They are the lowest and most primitive of the mammals and retain several structural characters of the lower vertebrates. Their most striking characteristic is that the young are not brought forth alive, but are hatched from eggs, as in the reptiles, birds and lower vertebrates generally. The second subclass, EUTHERIA, which includes all other mammals, is again divided into two very unequal groups or infraclasses. One of these, DrpELPHIA, contains but a single order, the Marsupialia, or pouched mammals, now in existence, and is also very primitive in many respects, though far more advanced than the Prototheria. The young, though born alive, 58 LAND MAMMALS IN THE WESTERN HEMISPHERE are brought forth in a very immature state and, with the excep- tion of one genus (Perameles) the foetus is not, attached by a special structure, the placenta, to the womb of the mother. Like the Prototheria, the Marsupials, which were once spread all over the world, are at present almost entirely confined to Australia and the adjoining islands, the Opossums of North and South America, and one small genus (Cenolestes) in the latter continent being the exceptions to this rule of distribution. The second and vastly larger infraclass, the MoNopDELPHIA, is characterized by the placenta, a special growth, partly of foetal and partly of maternal origin, by means of which the unborn young are attached to the mother and nourished during the foetal period; they are born in a relatively mature state and are generally able to walk immediately after birth and resemble their parents in nearly all respects. The vast assemblage of placental mammals, which range over all the continents, are divided into numerous orders, most of which appear to be natural groups of truly related forms, while some are but doubtfully so and others again are clearly unnatural and arbitrary. As has already been pointed out, the mutual relationships of these orders, as expressed in groups of higher than ordinal rank, offer a much more difficult problem, chiefly because our knowledge of the history of mam- mals is most deficient just where that history is most important and significant, namely, in its earlier portion. In many in- stances, the evolution of genera and families may be followed out within the limits of the order in a very convincing way, but very rarely can the origin of an order be demonstrated. When the history began to be full and detailed,the orders had nearly all been established, and, until the steps of their diver- gence and differentiation can be followed out, their mutual relationships can be discussed only from the standpoint of their likenesses and differences. In the valuation of these, there is much room for difference of opinion, and such difference is not lacking. On the other hand, concerning the number CLASSIFICATION OF THE MAMMALIA 59 and limits of the orders themselves there is very general agreement. In the following table only the major groups are included and those which are extinct are marked with a dagger (f). The scheme is almost identical with that given in Professor Osborn’s ‘‘ Age of Mammals,” the few points in which I should prefer a somewhat different arrangement being waived in the interests of uniformity and avoidance of confusion. A few changes are, however, made in matters which I regard as too important to ignore. I. Susctass PROTOTHERIA. Egg-laying Mammals. 1. OnpDER f PROTODONTA. 2. ORDER MONOTREMATA, e.g. the Duck-billed Mole and Spiny Anteaters. II. Susctass EUTHERIA. Viviparous Mammals. A. Inrractass DIDELPHIA. Pouched Mammals. 1. OnpER t TRICONODONTA. 2. OrpER MARSUPIALIA. a. SUBORDER Polyprotodonta. Opossums, carnivorous and insectivorous Marsupials. b. SUBORDER Diprotodonta. Herbivorous Marsupials; Kangaroos, etc. c. SuBORDER f Allotheria. B. Inrractass MONODELPHIA. Placental Mammals. AA. Consort UNGUICULATA. Clawed Mammals. 1. OrpER | TRITUBERCULATA. 2. OrpeR INSECTIVORA. Insect-eating Mammals. a. SUBORDER Lipotyphla, e.g. Moles, Hedgehogs, Shrews, etc. b. SuBsoRDER t Hyopsodonta. c. SuBORDER { Proglires. d. SUBORDER Menotyphla, e.g. Tree and Jumping Shrews. . ORvER ¢ TILLODONTIA. | . ORDER DERMOPTERA. The Flying Lemur. . OrpER CHIROPTERA. Bats. . ORDER CARNIVORA. Beasts of Prey. a. SuBORDER { Creodonta. Primitive Flesh-eaters. b. SuBORDER Fissipedia. Wolves, Bears, Weasels, Cats, etc. c. SUBORDER Pinnipedia. Marine Carnivores — Seals and Walruses. 7. ORDER RODENTIA. Gnawing Mammals. a. SUBORDER Duplicidentata, e.g. Hares, Rabbits, Pikas. O oP 60 LAND MAMMALS IN THE WESTERN HEMISPHERE BB. CC. b. SusorDER Simplicidentata, ¢.g. Squirrels, Marmots, Beavers, Rats, Mice, Porcupines, etc. 8. OrpEeR {| THNIODONTIA. 9. OnDER EDENTATA. a. SUBORDER Pilosa. Hairy Edentates, eg. Sloths, Ant- eaters, etc. b. SUBORDER Loricata. Armoured Edentates, e.g. Armadil- los, t Glyptodonts. 10. OnDER PHOLIDOTA. Scaly Anteaters or Pangolins. 11. OnpER TUBULIDENTATA. The Aard Vark. - Conort PRIMATES. Mammals with nails. 12. OnpER PRIMATES. a. SUBORDER Lemuroidea. Lemurs. b. SuBoRDER Anthropoidea. Monkeys, Apes, Man. Conort UNGULATA. Hoofed Mammals. 13. OrpER f CONDYLARTHRA. 14. OrpER | AMBLYPODA. 15. ORDER ARTIODACTYLA. Even-toed Hoofed Mammals. a. SUBORDER f{ Artiodactyla Primitiva. 6. SuBoRDER Suina. Swine, Peccary, Hippopotamus. c. SUBORDER Tylopoda. Camels, Llama, Guanaco. d. SuBORDER Tragulina. Mouse-deer or Chevrotains. e. SUBORDER Pecora, e.g. Deer, Antelopes, Sheep, Oxen, etc. 16. ORDER PERISSODACTYLA. Odd-toed Hoofed Mammals. a. SUBORDER Chelodactyla, e.g. Horses, Tapirs, Rhi- noceroses, etc. : 6. SuBoRDER'f Ancylopoda. f Chalicotheres. 17. OrpDER PROBOSCIDEA. Elephants and ¢ Mastodons. 18. OrpER | BARYTHERIA. 19. OrpER | EMBRITHOPODA. 20. OrpeR SIRENIA. Sea-cows and Dugongs. 21. OrpER HYRACOIDEA. Conies. 22. OrpER t TOXODONTIA, a. SUBORDER {| Toxodonta. b. SuBoRDER + Typotheria. c. SuBoRDER f{ Entelonychia. d. Susorper f Pyrotheria. 23. OrpER | ASTRAPOTHERIA. 24. OrpeR t LITOPTERNA. DD. Conort CETACEA. Whales, Dolphins, Porpoises. 25. OnpEr | ZEUGLODONTIA. 26. ORDER ODONTOCETI. Toothed Whales, Dolphins, Porpoises. 27. ORDER MYSTACOCETI. Whalebone Whales. CHAPTER IV THE SKELETON AND TEETH OF MAMMALS WITH very rare exceptions, and those only of the latest geological period (Quaternary), the fossil remains of mammals consist only of bones and teeth. The evolutionary changes, so far as these are preserved, are recorded therefore in terms of dental and skeletal modifications. To render these changes intelligible, it is necessary to give some account of the mam- malian skeleton and teeth, with no more use of ‘technical language than is unavoidable; ordinary speech does not furnish a sufficient number of terms, nor are most of these sufficiently precise. With the aid of the figures, the reader may easily gain a knowledge of the skeleton which is quite adequate for the discussion of fossil series, which will follow in the subsequent chapters. I. THe SKELETON I. The most obvious distinction of the skeletal parts is into axial and appendicular portions, the former comprising the skull, backbone or vertebral column, ribs and breastbone or sternum, and the latter including the limb-girdles, limbs and feet. In the axial skeleton only the ribs and certain bones of the skull are paired, but in the appendicular all the bones are in pairs, for the right and left sides respectively. The skull is a highly complex structure, made up of many parts, most of which are immovably fixed together, and per- forming many functions of supreme importance. In the first place, it affords secure lodgement and protection for the brain and higher organs of sense, those of smell, sight and hearing, 61 62 LAND MAMMALS IN THE WESTERN HEMISPHERE and second, it carries the teeth and, by its movable jaws, enables these to bite, to take in and masticate food. The portion of the skull which carries the brain, eyes and ears, is called the cranium, and the portion in front of this is the face, the boundary between the two being an oblique line drawn immediately in front of the eye-socket (Fig. 7). A great Fic. 7.—Skull of Wolf (Canis-occidentalis). P.Mz., premaxillary. Mz., maxillary. Na., nasal. L., lachrymal.- Ma., malar or jugal. Fr., frontal. Pa., parietal. - 8q., squamosal. Zyg., zygomatic: process of squamosal. O.S., orbitosphenoid. Pl., palatine. M., mandible. cor., coronoid process of mandible. m.c., condyle ‘of mandible. ang., angular process of mandible. p.g., postglenoid process of squamosal. Ty., tympanic (auditory bulla). mas., mastoid. p.oc., paroccipital process. con., occipital condyle. #z.0., exoccipital. S.O., supraoccipital. deal of the endless variety in the form of the skull of different mammals depends upon the differing proportions of cranium and face. In the human skull, for example, the cranium is enormously developed and forms a great dome, while the face is shortened almost to the limit of possibility ; the skull of the Horse, on the other hand, goes to nearly the opposite extreme of elongation of the facial and shortening of the cranial region. The posterior surface of the skull, or occiput, is made up of four bones, which in most adult mammals are fused into a single occipital bone. At the base of the occiput is a large opening, the foramen magnum, through which the spinal cord passes to its junction with the brain; and on each side of the opening is a large, smooth, oval. prominence, the occipital condyles, by means of which the skull is articulated with the SKELETON AND TEETH 63 neck. The paroccipital processes are bony styles of varying length, which are given off, one on each side external to the condyles. The boundary of the occiput is marked by a ridge, the occipital crest, which varies greatly in prominence, but is very well marked in the more primitive forms and tends to disappear in the more highly specialized ones. The roof and much of the sides of the cranium are formed by two pairs of large bones, the parietals behind and the frontals in advance ; along the median line of the cranial roof, where the two parietals meet, is usually another ridge, the sagittal crest, which joins the occipital crest behind. The sagittal crest also varies greatly in prominence, being in some mammals very high and in others entirely absent, and, like the occipital crest, is a prim- itive character; as a rule, it is longest and highest in those mammals which have the smallest brain-capacity. As pointed out by Professor Leche, the development of the sagittal crest is conditioned by the relative proportions of the brain-case and the jaws. Powerful jaws and a small brain-case necessitate the presence of the crest, in order to provide sufficient surface of attachment for the temporal muscles, which are important in mastication, while with large brain-case and weak jaws the crest is superfluous. Though the brain-case proper may be quite small, yet it may have its surface enormously increased by great thickening of the cranial bones, as is true of elephants and rhinoceroses, and in them sufficient surface for attachment is afforded to the muscles without the development of a crest. The structure of these cranial bones, more particularly of the parietals, is subject to important changes; in most mam- mals they are of moderate thickness and have dense layers, or ‘‘tables,”’ forming the outer and inner surfaces and, between these, a layer of spongy bone. In many large mammals, however, especially those which have heavy horns or tusks, the cranial bones become enormously thick and the spongy layer is converted into a series of communicating chambers, or sinuses, the partitions between which serve as braces, thus 64 LAND MAMMALS IN THE WESTERN HEMISPHERE making the bone very strong in proportion to its weight. Sinuses are very generally present in the frontals and communi- cate by small openings with the nasal passage, even in genera Fie. 8.—Skull of Wolf, top view. Fic. 9.—Skull of Wolf, view of base. ' P.Mz., premaxillary. Na., nasal. P.Mz., premaxillary. Mz., palatine Ma., malar or jugal. L., lachrymal. process of maxillary. Pl., palatine. Fr., frontal. Sg., squamosal. Pa., Fr., frontal. Pt., parietal. Ma., parietal. §.O., supraoccipital. malar or jugal.- Sq., glenoid ‘cavity of squamosal. ; B.S., basisphenoid. of moderate size and with- (aided: al axe, carob out horns or tusks. The process. con... occipital condyle. frontals form the roof of ence eae | the eye-sockets, or orbits, and usually there is a projection from each frontal, which marks the hinder border of the orbit and is therefore called the postorbital process. The roof of the facial region is made by the nasals, which are com- monly long and narrow bones, but vary greatly in form and SKELETON AND TEETH 65 proportions in different mammals; in those which have a proboscis, like tapirs and elephants, or a much inflated snout, such as the Moose (Alce) or the Saiga Antelope (Saiga tatarica) the nasals are always very much shortened and otherwise modified in form. The anterior end of the skull is formed by a pair of rather small bones, the premazillaries, which carry the incisor teeth; they bound the sides of the nasal opening, or anterior nares, reaching to the nasals, when the latter are of ordinary length ; they also form the front end of the hard or bony palate, which divides the nasal passage from the mouth. The mazillaries, or upper jaw-bones, make up nearly all of the facial region on each side and send inward to the median line from each side a bony plate which together constitute the greater part of the hard palate; the remainder of the upper teeth are implanted in the maxillaries. A varying proportion of the hinder part of the hard palate is formed by the palatines, which also en- close the posterior nares, the opening by which the nasal passage enters the back part of the mouth. The maxillary of each side extends back to the orbit, which it bounds anteriorly and in the antero-superior border of which is the usually small lachrymal. The inferior, and more or less of the anterior, border of the orbit is made by the cheek-bone (malar or jugal) which may or may not have a postorbital process extending up toward that of the frontal; when the two processes meet, the erbit is completely encircled by bone, but only in monkeys, apes and Man is there a bony plate given off from the inner side of the postorbital processes, which extends to the cranial wall and converts the orbit into a funnel-shaped cavity. For most of its length, the jugal projects freely outward from the side of the skull and extends posteriorly beneath a similar bar of bone, the zygomatic process of the sguamosal. This process and the jugal together constitute the zygomatic arch, which on each side of the skull stands out more or less boldly, and the size and thickness of which are subject to great variation in F 66. LAND MAMMALS IN THE WESTERN HEMISPHERE different mammals, the massiveness of the arch being pro- portional to the power of the jaws. One of the principal muscles of mastication (the masseter) is attached to the zygo- matic arch. The squamosal itself is a large plate, which makes up a great part of the side-wall of the cranium and articulates above with the frontal and parietal; it also supports the lower jaw, the articular surface for which is called the glenoid cavity. The lower jaw is held in place by the postglenoid process, which is a projection, usually a transverse ridge, behind the cavity. Back of the postglenoid process is the entrance to the middle ear, the auditory meatus, which may be merely an irregular hole, or a more or less elongated tube. The meatus is an opening into the tympanic, a bone which at birth is a mere ring and in some mammals remains permanently in that condition, but as a rule develops into a swollen, olive-shaped auditory bulla, which sometimes reaches enormous proportions, especially in nocturnal mammals. The labyrinth of the internal ear is contained in the periotic, a very dense bone which is con- cealed in the interior of the cranium, but in many mammals a portion of it, the mastoid, is exposed on the surface between the squamosal and occipital. The lower jaw-bone (inferior maxillary, or mandible) is the only freely movable element of the skull; it consists of two halves which meet anteriorly at the chin in a contact of greater or less length, called the symphysis. In nearly all. young mammals and in many adult forms the two halves of the lower jaw are separate and are held together at the symphysis only | by ligaments, while in others, as in Man, they are indistinguish- ably fused to form a single bone. Each half consists of two portions, a horizontal part or ramus and an ascending ramus or vertical part ; the former supports all of the lower teeth, and its length, depth and thickness are very largely conditioned by the number and size of those teeth. The ascending ramus is a broad, rather thin plate, divided at the upper end into two SKELETON AND TEETH 67 portions, the hinder one of which terminates in the condyle, a rounded, usually semicylindrical projection, which fits into the glenoid cavity of the squamosal. The anterior portion of the ascending ramus ends above in the coronoid process, which serves for the insertion of the temporal muscle, the upper portion of which is attached to the walls of the cranium and thus, when the muscle is contracted, the jaws are firmly closed ; the coronoid process passes inside of the zygomatic arch. The lower jaw is therefore a lever of the third order, in which the power is applied between the weight (7.e. the food, the resistance of which is to be overcome) and the fulcrum, which is the condyle. At the postero-inferior end of the ascending ramus is the angle, the form of which is characteristically modified in the various mammalian orders and is thus employed for purposes of classification. The hyoid arch is a U-shaped series of small and slender bones, with an unpaired element closing the arch below; each vertical arm of the U is attached to the tympanic of its own side and the whole forms a flexible support for the tongue, but with no freely movable joint like that between the lower jaw and the squamosal. The mammalian skull in its primitive form may be thought of as a tube divided into two parts, of which the hinder one is the brain-chamber, or cranial cavity, and the forward one the nasal chamber or passage. With the growth of the brain and consequent enlargement of the cranium, this tubular character is lost ; and various modifications of the teeth, jaws and facial region, the development of horns and tusks, bring about the many changes which the skull has undergone. This brief sketch of the skull-structure is very incomplete, several of its elements having been altogether omitted and only those parts described which are needful in working out the history and descent of the various mammalian groups. The second portion of the axial skeleton is the backbone, or vertebral column, which is made up of a number of separate 68 LAND MAMMALS IN THE WESTERN HEMISPHERE bones called vertebra. These are so articulated together as to permit the necessary amount of flexibility and yet retain the indispensable degree of strength. The function of the back- bone is a twofold one: (1) to afford a firm support to the body and give points of attachment to the limbs, and (2) to carry the spinal cord, or great central axis of the nervous system, in such a manner that it shall be protected against injury, a matter of absolutely vital necessity. While the vertebre differ greatly in form and appearance in the various regions of the neck, body and tail, in adaptation to the various degrees of mobility and strength which are required of them, yet they are all constituted upon the same easily recognizable plan. The principal mass of bone in each vertebra is the body, or centrum, which is typically a cylinder, or modification of that form, and the two ends of the cylinder are the faces, by which the successive vertebre are in contact with one another. In the living ariimal, however, the successive centra are not in actual contact, but are separated by disks of cartilage (gristle) which greatly add to the elasticity of the column. From the upper surface of the centrum arises an arch of bone, the neural arch, enclosing with the centrum the neural canal, through which runs the spinal cord. As already mentioned, the protection of the spinal cord is essential to the life of the animal, yet this protection must be combined with a certain flexibility, both lateral and vertical. Mere contact of the centra, even though these be held in place by ligaments, would not give the column strength to endure, without dis- location, the great muscular stresses which are put upon it. Additional means of articulation between the successive vertebre are therefore provided, and these vary in size, form and position in different regions of the backbone, in nice adjust- ment to the amount of motion and degree of strength needed at any particular part of the column. Of these additional means of articulation, which are called the zygapophyses, each vertebra has two pairs, an anterior and a posterior pair, placed SKELETON AND TEETH 69 upon the neural arch. From the summit of the arch arises the neural spine, a more or less nearly straight rod or plate of bone, which may be enormously long or extremely short, massive or slender, in accordance with the muscular attach- ments which must be provided for. Finally, should be men- tioned the transverse processes, rod-like or plate-like projections of bone, which arise, one on each side of the vertebra, usually from the centrum, less commonly from the neural arch ; these also differ greatly in form and size in the various regions of the column. ‘ Anatomists distinguish several other pro- ee ae es cesses of the vertebra, but for our purpose it is not necessary to take these into con- sideration. Five different regions of the backbone may be distinguished, in each of which the vertebree are modified in a characteristic vertebra of Wolf from the front. cn., centrum. r., facet for the head of the rib. vr’., facet for the tubercle of the rib. ér., transverse process. pr.z., ante- rior zygapophyses. way. There is (1) the cervical region, or 8?» neural spine. neck, the vertebre of which, among mammals (with only one or two exceptions) are always seven in number, however long or short the neck may be; the immoderately long neck of the Giraffe has no more and the almost invisible neck of the Whale has no less, and thus the elongation of the neck is accomplished by lengthening the individual vertebre and not by increasing their number. (2) Those vertebre to which ribs are attached are named dorsal or thoracic and can always be recognized by the pits or articular facets which receive the heads of the ribs. (3) Behind the dorsal is the lumbar region, or that of the loins, made up of a num- ber of vertebree which carry no ribs. The dorso-lumbars are known collectively as the trunk-vertebre and are generally quite constant in number for a given group of mammals, though often differently divided between the two regions in different members of the same group. In the Artiodactyla, for example, 70 LAND MAMMALS IN THE WESTERN HEMISPHERE there are very constantly 19 trunk-vertebre, but the Hippo- potamus has 15 dorsals and 4 lumbars, the Reindeer (Rangifer) 14.D., 5 L., the Ox (Bos taurus) 13 D., 6 L., the Camel (Camelus dromedarius) 12 D. and 7 L. (4) Next follows the sacrum, which consists of a varying number of coalesced vertebre. The number of sacral vertebre varies from 2 to 18, but is usually from 3 to 5. (5) Finally, there are the caudal vertebra, or those of the tail, which are extremely variable in number and size, depending upon the length and thickness of the tail. We must next consider briefly some of the structural features which characterize the vertebre of the different regions. (1) The length of the neck varies greatly in different mammals and, up to a certain point, flexibility increases with length, but, as the number of 7 cervicals is almost universally constant among mammals and the lengthening of the neck is accom- plished by an elongation of the individual vertebre, a point is eventually reached, where greater length is accompanied by a diminution of mobility. For instance, in the Giraffe the movements of the neck are rather stiff and awkward, in striking contrast to the graceful flexibility of the Swan’s neck, which has 23 vertebre, more than three times as many. The first two cervical ver- tebre are especially and pecul- iarly modified, in order to support the skull and give to Fig. 11.— Atlas of Wolf, anterior end and it the necessary degree of mo- neural canal," ma, neweal arch, ir, bility upon the neck. The first eer oat tt tie Peaeey ertebra, or alas, is hardly artery. more than a ring of bone with a pair of oval, cuplike depres- sions (anterior cotyles) upon the anterior face (superior in Man) into which are fitted the occipital condyles of the skull. By the rolling of the condyles upon the atlas is effected the nodding movement of the head, upward and down- ward, but not from side to side; this latter movement is, ‘SKELETON AND TEETH 71 accomplished by the partial rotation of skull and atlas to- gether upon the second vertebra in a manner presently to be explained. On the hinder aspect are two articular surfaces (posterior cotyles) in shape like the anterior pair, but very much less concave, which are in contact with corresponding surfaces on the second vertebra. The neural arch of the atlas is broad and low and the neural canal is apparently much too large for the spinal cord, but, in fact, only a part of the circular opening belongs to the neural canal. In life, the opening is divided by a transverse ligament into an upper portion, the true neural canal, and a lower portion, which lodges a pro- jection from the second vertebra. The atlas usually has no neural spine and never a prominent one; the transverse processes are broad, wing-like plates and each is perforated by a small canal, which transmits the vertebral artery. The second vertebra, or axis, is a little more like the ordi- nary vertebra, having a definite and usually elongate centrum, on the anterior end of which are the two ar- ticular surfaces for the atlas. Between these is a prominent projection, the odontoid pro- cess, which fits into the ring of the atlas and has a special articulation with the lower bar Nah aie aie on of that ring. In most mammals the odon- toid process. cot., an- é ‘ a é terior cotyles. n.a., toid process is a bluntly conical peg, varying jcural arch. nsp. merely in length and thickness, but in many neural spine. pt.z., ‘ ‘ posterior zygapophy- long-necked forms the peg is converted into a ges. tr., transverse pro- semicylindrical spout, convex on the lower cess. 4’, anterior 7 opening of canal for side and concave above. Theneural spine of the vertebral artery. the axis is almost always a relatively large, — _ ee epan hatchet-shaped plate, which is most developed in the carnivorous forms, and the transverse processes are com- monly slender rods. The five succeeding cervical vertebre are much alike, though each one has a certain individuality, by which its place in the series may readily be determined. The centrum has a convex 72 LAND MAMMALS IN THE WESTERN HEMISPHERE anterior and concave posterior face, which in long-necked ani- mals form regular ‘‘ball and socket”’ joints; neural spines are Fie. 13. — Fifth cervical verte- bra of Wolf, left side. ¢r., trans- verse process. v.a"’., posterior opening of canal for the vertebral ar- tery. pr.z.and ptl.z., anterior and posterior uy gapophyses. n.sp., neural spine. ribs. frequently wanting and, when present, are almost always short and slender; the zygapophyses are . very prominent and are carried on projections which extend before and behind the neural arch ; the transverse processes are long, thin plates and, except in the seventh cervical, are usually pierced by the canal for the vertebral artery, but in a few forms (e.g. the camels) this canal pierces the neural arch. (2) The dorsal or thoracic vertebre have more or less cylindrical centra, with nearly flat faces, and on the centra, for the most part at their ends, are the concave facets for the rib-heads. The transverse processes are short and rod-like and most of them articulate with the tubercles of the The zygapophyses are smaller than in the cervical region, less prominent and less oblique; the anterior pair, on the front of the neural arch, face upward and the posterior pair down- ward. The neural spines are very much longer than those of the neck and those of the anterior -dorsals are often of relatively enormous length, diminishing toward the hinder part of the region. (3) The lumbar vertebre are almost always heavier and larger than those of the dorsal region ; they carry no ribs and their neural spines and transverse processes are broad and plate-like and the latter are far larger and more prominent than those of the dorsals. As an especial degree of strength is frequently called for in the loins, to- gether with a greater flexibility than is needed in the dorsal region, the modes of articulation between the successive vertebrae are more com- plex, sometimes, as in the Edentata, most elabo- Fig. 14.— First dorsal vertebra of Wolf, left side. c., centrum. 7., anterior rib- facet. r’’., pos- terior rib-facet. tr., transverse process. opr.z. pt.z., anterior and posterior zyga- pophyses. n.sp., neural spine. SKELETON AND TEETH 73 rately so. Taking the dorso- lumbars, or trunk-vertebre, as a single series, we may note that in a few mammals (e.g. the ele- i phants) all the neural spines © have a backward slope but in Fig. 15. — Third lumbar vertebra of Wolf, ae : front end and left side. ¢r., transverse the great majority of forms process. cn., centrum. pr.z. and pi.z., this backward inclination ceases *"*etor and posterior zygapophyses. . n.sp., neural spine. near the hinder end of the dor- sal region, where there is one vertebra with erect spine, while behind this point the spines slope forward. (4) The sacral vertebre, varying from 2 to 13 in number, are fused together solidly into one piece, the combined centra forming a heavy mass and the neural canals a continuous tube, while the neural spines are united into a ridge. As a rule, only the first two vertebre of the sacrum are in contact with the hip-bones, to support which they have de- veloped special processes, the remainder of the zh aE ae mass projecting freely backward. side. I, I, III, (5) The caudal vertebre vary greatly, in first, second and 4 scordance with the length and thickness of the third sacral verte- bre. pl., surface tail, In an animal with well-developed tail co " several of the anterior caudals have the parts and processes of a typical vertebra, centrum, neural arch and spine, zygapophyses and transverse processes. Posteriorly, these gradually diminish, until only the centrum is left, with low knobs or ridges, which are the remnants of the various processes. A mine e=3 varying number of long, cylindrical centra, re diminishing backward in length and diame- a ea ter, complete the caudal region and the ver- __rior and middle parts of tebral column. In some mammals, chevron ei ees bones are attached to the under side of the anterior and middle caudals; these are forked, Y-shaped bones, 74 LAND MAMMALS IN THE WESTERN HEMISPHERE which form a canal for the transmission of the great blood-ves- sels of the tail. The ribs, which are movably attached to the backbone, together with the dorsal vertebre and breast-bone, compose the thorax, or chest. The articulation with the vertebre is by means of a rounded head; in most cases the head has two distinct facets, the pit being formed half on the hinder border of one dorsal vertebra and half on the front border of the next suc- ceeding one, but posteriorly the pit is often shifted, so as to be on a single vertebra. A second articulation is by means of the tu- bercle, a smooth projecting facet on the con- vexity of the rib’s curvature and near the head; the tubercle articulates with the transverse process of its vertebra. Theribs, in general, are curved bars of bone, which in small mammals generally and in the Sige ane clawed orders are slender and rod-like, while from anterior and im the hoofed mammals they are broader, middle parts of the thinner and more plate-like, especially the thorax. cp., head. t., . < tubercle. anterior ones. The number of pairs of ribs is most commonly 13, but ranges among existing mammals from 9 in certain whales to 24 in the Two-toed Sloth (Cholepus didactylus). The complex curvature of the ribs, outward and backward, is such that, when they are drawn forward (in Man upward) by muscular action, the cavity of the thorax is enlarged and air is drawn into the lungs, and when they are allowed to fall back, the cavity is diminished and the air expelled. Below, a varying number of the ribs are connected by the cartilages in which they terminate with the breast-bone (sternum) ; sometimes these cartilages are ossified and then form the sternal ribs, but there is always a flexible joint between the latter and the true ribs. In certain edentates, notably SKELETON AND TEETH 75 the anteaters and the extinct + ground-sloths, these sternal ribs, at their lower ends, are provided with head and tubercle, for articulation with the sternum. The sternum, or breast-bone, is made up of a number of distinct segments, usually broad and flat, but often cylindrical, which may “unite, but far more commonly remain separate throughout life. The number, size and form of these segments often give useful characters in classification. The first seg- ment, or manubrium, has quite a different shape from the suc- ceeding ones and is consider- ably longer. II. The appendicular skeleton consists of the limb- girdles and the bones of the limbs and feet. The limb- girdles are the means of at- taching the movable limbs to the body, so as to combine the necessary mobility with strength. The anterior, or shoulder-girdle, has no direct articulation with the vertebral column, but is held in place by muscles; it is made up of the shoulder-blade and collar- bone, though very many mam- mals have lost the latter. The shoulder-blade, or Fic. 19.—Sternum and rib-cartilages of i Wolf, lower side. P.S., manubrium. scapula, is a broad, thin, plate- , S., xiphisternum. like bone, which contracts be- low to a much narrower neck, ending in a concave articular surface, the glenoid cavity, for the head of the upper arm-bone, the two together making the shoulder-joint. On the outer side 76 LAND MAMMALS IN THE WESTERN HEMISPHERE the blade is divided into two parts by a prominent ridge, the spine, which typically ends below in a more or less con- Fic. 20. — Leftscapulaof Wolf. gl., glenoid cavity. c., cora- coid. ac., acromion. sp. spine. Fic. 21.— Left scapula of Horse. gt wt’ aul, This figure is much more reduced ! than Fig. 20. » gah spicuous projection, the acromion, which may, however, be absent, its prominence being, generally speaking, correlated Fic. 22.—Left scapula of Man in position of walking on all fours. Letters as in Fig. 20. with the presence of the collar bone. A_ hook-like process, the coracoid, rises from the antero-internal side of the glenoid cavity and varies greatly in size in the different groups of mammals; though it usu- ally appears to be merely a process of the scapula, with which it is indistinguish- ably fused, yet its development shows it to be a separate ele- ment and in the lowest mammals (Prototheria), as in the rep- SKELETON AND TEETH 77 tiles and lower vertebrates generally, it is a large and im- portant part of the shoulder-girdle and articulates with the sternum. . The collar-bone, or clavicle, is a complexly curved bar, which, when present and fully developed, extends from the forward end of the sternum to the acromion, the projecting lower end of the scapular spine, supporting and strengthening the shoulder-joint. In many mammalian orders, notably all existing hoofed animals, the = SOY clavicle has become superfluous Fie. 23. — Left clavicle of Man, front side. and is lost more or less com- pletely ; it may be said, in general, that the clavicle is devel- oped in proportion to the freedom of motion of the shoulder- joint and to the power of rotation of the hand upon the arm. In arboreal animals, such as monkeys, in which the hand rotates freely and the arm moves in any direction on the shoulder, the clavicle is large and fully developed, as it also is in Man. Many burrowing mammals (e.g. the moles) have very stout clavicles. The posterior, or pelvic, girdle is composed on each side of a very large, irregularly shaped bone, which is firmly attached to one or more of the coalesced vertebre which form the sacrum and thus affords a solid support to the hind leg. Each half of the pelvis, or hip- bone, is made up of three elements, called respectively the ilium, ischium and pubis, which are Separate in 7 the very young animal, Fic. 24.— Left hip-bone of Wolf. Jv., ilium. Is., . i ape ‘ ischium. P., pubis. ac., acetabulum. indistinguishably fused in the adult. The three elements unite in a deep, hemispherical pit, the acetabulum, which receives the head of the thigh-bone, a perfect ex- 78 LAND MAMMALS IN THE WESTERN HEMISPHERE ample of the ‘‘ball and socket joint.’ In the inferior median line the two pubes meet and may become coalesced, in a sym- physis, the length of which differs in various mammals. The pelvis and sacrum together form a short, wide tube, the diame- ter of which is normally greater in the female skeleton than in the male. The limbs are each divided into three segments, which in the anterior extremity are the arm, fore-arm and hand. (or fore foot) and in the posterior extremity are the thigh, leg and foot (or hind foot), and there is a general correspondence between the structure of these segments in the fore and hind legs, however great the superficial difference. The bones of the limbs, as distinguished from those of the feet, are the long bones and, except in a few very large and heavy mammals, are essentially hollow cylinders, thus affording the maximum strength for a given weight of bone; the cavity of a long bone contains the marrow and hence is called the medullary cavity. In the young mammal each of. the long bones consists of three parts, the shaft, which makes up much the greater part of the length, and at each end a bony cap, the epiphysis. Growth takes place by the intercalation of new material between the shaft and the is Fe ext opr Fia. 25.— Left humerus of Wolf, from the front and outer sides, the latter somewhat oblique. h., head. int.t., internal tuberosity. ezt.t., external tuberosity. be., bicipital groove. di., deltoid ridge. sh., shaft. s., supinator ridge. int. epi. internal epicondyle. s.f. anconeal foramen. tr., trochlea. tr’., trochlea, posterior side. ext. epi. external epicondyle. a.f. anconeal fossa. epiphyses; when the three parts unite, growth ceases and the ani- mal is adult. The superior segment of the fore limb has a single bone, the humerus, the upper end of which SKELETON AND TEETH is the rounded, convex head, which fits into the glenoid cavity of the shoulder-blade, form- ing the joint of the shoulder; in front of the head are two prominent and sometimes very large projections for muscular attach- ment, the external and internal tuberosities, sep- arated by a groove, in which play the two ten- dons of the biceps muscle and is therefore called the bicipital groove. Inafew mammals, such as the Horse, Camel and Giraffe, the groove is divided into two by a median tubercle or ridge. From the external tuberosity there generally passes down the front face of the shaft a rough and sometimes very prominent ridge, the deltoid crest, to which is attached the At Fic, 26.— Left hu- merus of Horse, front side. i.¢., in- ternal tuberosity. ez.t., external tu- berosity. bc., outer part of bicipital groove. dt., del- toid ridge. »s., su- pinator ridge. r., trochlea. Fic. 27.— Left hu- merus of Man, front side. Let- ters as in Fig. 25. powerful deltoid muscle. the lower end of the humerus is the trochlea, an irregular half-cylinder, for articulation with the two bones of the fore-arm and vary- ing in form according to the relative sizes of those bones. On each side of the troch- lea is frequently a rough prominence, the epr- condyle, and above the inner one is, in many mammals, a perforation, the epicondylar fora- men, for the passage of a nerve. Extending up the shaft from the outer epicondyle is a rough crest, the supinator ridge, to which is attached one of the muscles that rotate the hand and is conspicuously developed in those mammals which have the power of more or less free rotation and especially in burrow- ers. On the posterior face of the humerus, 80 LAND MAMMALS IN THE WESTERN HEMISPHERE just above the trochlea, is a large, deep pit, the anconeal fossa. The two bones of the fore-arm, the radius and ulna, are, in most mammals, entirely separate from each other, but in certain of the more highly specialized hoofed animals are immovably codssified. Primitively, the two bones were of Fic. 28.— Left fore-arm bones of Wolf, Fie. 29.— Left fore-arm bones of Man, front side. #.,radius. U., ulna. ol., front side. Letters as in Fig. 28. The olecranon. h., head of radius. small object at the right of each figure is the head of the radius, seen from above. nearly equal size, but in most of the mammalian orders there is a more or less well-defined tendency for the radius to enlarge at the expense of the ulna. These bones are normally crossed, the radius being external at the upper end and passing in front of the ulna to the inner side of the arm. The radius varies considerably in form in accordance with the uses to which the SKELETON AND TEETH 81 hand is put; if the capacity of rotation is re- tained, the upper end, or head, of the radius is small, circular or disk-like, covering little of the humeral trochlea, but when the head of the radius is broadened to cover the whole width of the humerus, then all power of rota- tion islost. (Cf. Figs. 28 and 29.) As a rule, the radius broadens downward and covers two-thirds or more of the breadth of the wrist-bones. The ulna is longer than the radius, its upper end being ex- tended into a heavy process, the olecranon, or anconeal process, into which is inserted the tendon s of the great triceps muscle, the p,, 39.—Coss- contraction of which straightens ee ¢ the arm ; this processis the bony Horse, front projection at the back of the el- ea bow-joint. Below the olecranon _ the ulna iscon- is a semicircular articular con- ics oa aad cavity, which embraces the hume- ral trochlea and its upper angle fits into the anconeal fossa of the humerus. The ulna con- tracts and grows more slender downwards and its lower end covers but one of-the wrist-bones. Fie. 31. —Left fore. While in the more primitive mammals, and in arm bones of the those which retain the power of rotating the Tapir (Tapirus . terrestris). R., ra~ hand, the ulna has nearly or quite the same dius, U.,wina. h-+ thickness as the radius, it is often much more head of radius. h’., sigmoid notch of slender and in the more highly specialized of Ina. ol., ole- : oronen. NB. This the hoofed animals, such as the horses, camels figure ison amuch and true ruminants, the radius carries the en- larger scale than , ‘s Fig. 30. tire weight and the ulna has become very slen- G 82 LAND MAMMALS IN THE WESTERN HEMISPHERE der, more or less of its middle portion is lost and the two ends are codssified with the radius, so that the fore-arm appears to have but a single bone. The reverse process of enlarging the ulna and reducing the radius is very rare and practically con- fined to the elephant, tribe. The fore foot, or hand, for which the term manus may be conveniently employed, is divisible into three parts, correspond- ing in ourselves to the wrist, back and palm of the hand, and the fingers. The bones of the wrist constitute the carpus, Fic. 32.— Left manus of Wolf, front Fic. 33.— Left manus of Man. S., sca side. SL.,scapho-lunar. Py., pyram- phoid. L., lunar. Py., pyramidal (pisi- idal. Pis., pisiform. Tm., trape- form not shown). 7'm., trapezium. Td., ,zium. Td., trapezoid. M., magnum. trapezoid. M.,magnum. Un., unciform. U., unciform. Mc.I-V, first to fifth Other letters as in Fig. 32. metacarpals. Ph.i, first phalanx. Ph.2, second phalanx. Ung., ungual phalanx. J, first digit, or pollex. IJ-V, second to fifth digits. those of the back and palm the metacarpus, and those of the fingers the phalanges. . 5 The carpus consists primitively of nine distinct bones, though one of these, as will be shown later, is not a true carpal. These bones are of a rounded, subangular shape, closely ap- SKELETON AND TEETH 83 pressed together, with very little movement between them, and are arranged in two transverse rows. The upper row con- tains four bones, which enumerating from the inner side are the scaphoid, lunar, pyramidal (or cuneiform) and pisiform. The scaphoid and lunar support the radius, while the ulna rests upon the pyramidal. The pisiform, though very con- stantly present, is not a true carpal, but an ossification in the tendon of one of the flexor muscles, which close the fingers ; it projects more or less prominently backward and articulates with the ulna and pyramidal. The second row is also made up of four bones, which, from within outward, are the trape- zium, trapezoid, magnum and unciform. The relations of the two rows vary much in different mammals and the arrange- ment may be serial or alternating; thus, the scaphoid rests upon the trapezium and trapezoid and usually covers part of the magnum; the lunar may rest upon the magnum only, but very much more frequently is equally supported by the magnum and unciform and the pyramidal by the latter only. The ninth carpal is the central, which, when present and dis- tinct, is a small bone, wedged in between the two rows. Few existing mammals have a separate central, which, though present in the embryo, has coalesced with the scaphoid in the great majority of forms. In the more advanced and differ- entiated mammals the number of carpals may be consider- ably reduced by the codssification of certain elements or the complete suppression and loss of others. In all existing Carnivora and a few other mammals the scaphoid and lunar are united in a compound element, the scapho-lunar (or, more accurately, the scapho-lunar-central); hoofed animals with a diminished number of toes generally lose the trapezium, and other combinations occur.’ The second row of carpals carries the metacarpals, and primitively the trapezium, trape- zoid and magnum are attached each to one metacarpal and the unciform has two. The metacarpus consists typically of five members, a num- 84 LAND MAMMALS IN THE WESTERN HEMISPHERE ber which is never exceeded in any normal terrestrial mammal ; the members are numbered from the inner side, beginning with the thumb or pollex, from I to V. Many mammals have fewer than five metacarpals, which may number four, three, two or only one; the third is never lost, but any or all of the others may be suppressed, and functionless rudiments of them may long persist as splints or nodules. The metacarpals are elongate, relatively slender and of more or less cylindrical shape; but the form varies considerably in different groups, according to the way in which the hand is used. When em- ployed for grasping, as in many arboreal animals and pre- eminently in Man, the pollex is frequently opposable to the other fingers and enjoys much freedom of motion. In the camels and true ruminants the third and fourth metacarpals are coéssified to form a cannon-bone (see Fig. 43, p. 91), but the marrow cavities and the joints for the phalanges remain separate. The phalanges in land mammals never exceed three in each digit, except the pollex, which, when present and fully developed, has but two. The phalanges are usually slender in proportion to their length, but in very heavy hoofed animals they are short and massive. The terminal joint is the ungual phalanz, which carries the nail, claw, or hoof, its shape varying accordingly. The hind leg is constituted in very much the same manner as the fore, but with ‘certain well-marked and constant dif- ferences. The thigh-bone, or femur, is usually the longest and stoutest of the limb-bones and in very large animals may be extremely massive. At the upper end is the hemispherical head, which is set upon a distinct neck and projects inward and upward, fitting into the acetabulum of the hip-bone. Nearly all land mammals have a small pit on the head of the femur, in which is inserted one end of the round ligament, while the other end is attached in a corresponding depression in the floor of the acetabulum. This ligament helps to hold the thigh- bone firmly in place and yet allows the necessary freedom of SKELETON AND TEETH 85 movement. On the outer side of the upper end of the femur is a large, roughened protuberance, which often rises higher gt.tn datcons jE eact. con — : Fic. 34. — Left femur of Wolf, front side. Fic. 35.— Left femur of Horse. tr .3, h., head. gt.tr., great trochanter. ¢r. 2, third trochanter. Other letters as in second trochanter. int.con., internal Fig. 34, than which this drawing is condyle. 7.g., rotular groove. ezt. very much more reduced. con., external condyle. than the head and is called the great trochanter; another, the second or lesser trochanter, is a small, more or less conical prom- inence on the inner side of the shaft, below the head. These two processes are well-nigh universal among land mammals ; and in a few of the orders occurs the third trochanter, which arises from the outer side of the shaft, usually at or above the middle of its length. Though comparatively rare in the modern world, the third trochanter is an important feature, and the early members of most, if not all, of the mammalian orders possessed it. The shaft of the femur is elongate and, except in certain very bulky mammals, of nearly cylindrical shape. The lower end of the bone is thick and heavy and bears 86 LAND MAMMALS IN THE WESTERN HEMISPHERE on the posterior side two large, rounded prominences, the condyles, which articulate with the shin-bone to form the knee-joint. On the anterior side is a broad, shal- Q ) low groove, the rotular groove, in which glides the patella, or knee-cap. The patella is a large ossification, of varying shape, in the tendon com- mon to the four great extensor muscles of the thigh, the action of which is to straighten the leg. The lower leg, like the fore-arm, has two LG GF bones, which, however, are always parallel, never unt.eon. crossed, and have no power of rotation. Of nein oe i these, the inner one is the shin-bone, or tibia, side of lower end. which is always the larger and alone enters into oie ae the knee-joint. The external bone is the fibula, ee which is almost entirely suppressed in certain ular groove. highly specialized forms, such as the horses and Above, are two ruminants, the tibia carrying the whole weight. sola. ne The upper end of the tibia is enlarged and ex- a internal tends over that of the fibula; it has two slightly concave surfaces for articulation with the con- dyles of the femur, the approximate edges of which are raised into abifid spine. The upper part of the shaft is triangular, with one edge directed forward, and the superior end of this edge is rough- ened and thickened to form the cnemial crest, to which is at- tached the patellar ligament. The middle portion of the shaft is rounded and the lower end broad and usually divided by a ridge into two grooves or concavities for the ankle-bone ; from the in- ner side of this end projects downward a tongue-like process, the internal malleolus, which prevents inward dislocation of theankle. The fibula is relatively stoutest in the less advanced mam- mals and is usually straight and slender, with enlarged ends, the lower one forming the external malleolus, which serves to prevent outward dislocation of the ankle. In many forms the fibula is codssified with the tibia at both ends, and in the most highly specialized hoofed animals, such as the horses, SKELETON AND TEETH 87 camels and true ruminants, the bone has apparently disap- peared. The young animal, however, shows that the ends of the fibula have been retained and the shaft completely lost ; the upper end is in the adult firmly fused with the tibia and, Fic. 37. — Bones of left lower leg of Wolf, front side. T., tibia. F., fibula. sp. spine of tibia. cn. cnemial crest. i.m., internal malleolus. ¢m., ex- ternal malleolus. cm ~ e.7M. Fic. 38. — Bones of left lower leg of Horse (much more reduced). cn. cnemial crest. F., lower end of fibula, coéssified with tibia. Other letters as in Fig. 37. Fic. 39. — Bones of lower leg, left side, of Tapir. T., tibia. F., fibula. sp., spine of tibia. cn., enemial crest. ¢.m., in- ternal malleolus. ¢.m., external malleolus. N.B. This figure is-on amuch larger scale than Fig. 38. in the horses, the lower end is also, but this remains separate in the ruminants and camels, forming the malleolar bone, which is wedged in between the tibia and the heel-bone. Because of its importance in holding the ankle-bone in place, this lower end of the fibula is never lost in any land mammal. The hind foot, or pes, like the manus, is clearly divisible 88 wy Fia. 40. — Left pes of Wolf, front side. Cal., calca- neum. As., astragalus. N., navicular. boid. Cn.1,Cn.2, Cn. 3, internal; middle and ex- ternal cuneiforms. Mt.I, rudimentary first meta- tarsal. Mt. IJ-V, second to fifth metatarsals. Ph. 1, first phalanx. Ph. 2, second phalanx. Ung., ungual phalanx. I, rudimentary hallux. II-V, second to fifth digits. Ch., cu- LAND MAMMALS IN THE WESTERN HEMISPHERE into three parts, the bones of which are called respectively the tarsus, metatarsus and phalanges, and the correspondence in structure between manus and pes is close and obvious. The tarsus consists typi- cally of seven bones, which are tightly packed and rarely permit any movement between them. The upper row of the tar- sus consists of two bones, which are pe- culiarly modified to form the ankle-joint and heel; on the inner side is the ankle- bone, or astragalus, the shape of which is highly characteristic of the various mam- malian orders. The upper or posterior portion of the astragalus, according to the position of the foot, is a pulley which glides upon the lower end of the tibia and is held firmly in place by the internal and the external malleolus. Below the pulley-like surface the astragalus usually contracts to a narrow neck, which ends in a flat or convex head. The astragalus is sup- ported behind (or be- neath) by the heel-bone, or calcanewm, which is elongate and extends well above (or behind) the remainder of the tarsus ; it frequently has a distinct articulation with the fibula, but more commonly is not in contact with that bone. The astragalus rests upon the navicular, which Fic. 41.— Left pes of Man, Note thelarge size of Mt. I, the met- atarsal of the first digit, or hallux. Let- ters as in Fig. 40, ex- cept Cb., cuboid. SKELETON AND TEETH 89 is moulded to fit its head and corresponds in position to the cen- tral of the carpus, but, unlike that carpal, it is a very important element and is never suppressed or lost in any land mammal. The navicular, in turn, rests upon three bones of the second row, which are called respectively the internal, middle and external cu- neiform, which correspond to the trapezium, trapezoid and mag- num of the carpus and to which are attached the three inner met- atarsals, one to each. Finally, the cuboid, the external element of the second row, is a large bone, which supports the caleaneum and often part of the astragalus and to which the fourth and fifth metatarsals are attached ; it is the equivalent of the unci- form in the manus. The number of tarsals is more constant than that of the carpals, but some suppressions and coéssi- fications do occur. The long bones of the pes constitute the metatarsus, which is the counterpart of the metacarpus. There are never more than five metatarsals in any normal mammal, but there may be any number less than five, down to a single one. In form and size the metatarsals of any given mammal are usually so like the metacarpals, that it requires some experience to distinguish them, but when either manus or pes is especially adapted to some particular kind of work, there may be very decided differences between metatarsals and metacarpals. For example, the burrowing forefoot of the moles is very different from the hind foot, which has undergone but little modification, and even more striking is the difference between the wing of a bat and its foot. Many other instances of a less extreme diver- gence might be enumerated, but when manus and pes are used only for locomotion, as in nearly all hoofed animals and many other mammals, the metacarpals and metatarsals are very similar. When there is a difference in number, it is the general rule that there are fewer metatarsals; an instance of this is found in the tapirs, which have four toes in the front foot and three in the hind. Forms which have a cannon-bone in the manus have it also in the pes, and some, like the peccaries and 90 LAND MAMMALS IN THE WESTERN HEMISPHERE the jumping rodents called jerboas, have it only in the pes. The first (or inner) metatarsal, that of the great toe, or halluz, is sometimes opposable to the others, as in the monkeys, apes and lemurs. The word metapodial is a useful general term which in- cludes both metacarpals and metatarsals. A metapodial with its phalanges is a digit, a term often employed because of the ambiguity which arises in the use of the words “‘fingers”’ and ‘“‘toes,’”’ and is applicable to both fore and hind feet. Normally, the phalanges of the pes are so like those of the manus as to require no particular description ; and only when the two pairs of extremities are specialized for entirely different functions, is there any notable divergence between the pha- langes of manus and pes. Before leaving the subject of the skeleton, it will be well to explain the terms used in describing the gait and manner of using the feet. When the entire sole of the foot is in contact with the ground and weight is thrown upon the heel-bone, or calcaneum, the gait is said to be plantigrade and is exem- plified in Man, bears, raccoons and many other mammals. The Dog is digitigrade, that is to say, the feet in the stand- Fic. 42.— Left pes of Black Bear (Ursus americanus), showing the plantigrade gait. T., tibia. F., fibia. Cal., calcaneum. As., astragalus. N., navicular. Cn. 3, external cuneiform. Cb., cuboid. Mt.V, ing position are nearly erect and the wrist and heel are raised high above the ground ; the weight is borne upon ball- fifth metatarsal. _ like pads, one under the pha- langes of each functional digit and one under the metapo- dials. The digitigrade gait is found not only in all the dogs and cats, but in many other Carnivora and in the camels and llamas, as well. Transitions between the plantigrade and digitigrade gait are so numerous and gradual, that such terms as semi-plantigrade and semi-digitigrade are sometimes necessary. SKELETON AND TEETH 91 An animal is said to be unguli- grade when the weight is carried entirely upon the hoofs and is used only of hoofed animals; ex- amples are the horses, pigs, deer, antelopes, oxen, etc. The so- called ‘‘knee”’ of a horse is really his wrist and the ‘‘hock”’ is the heel, so that the feet make nearly half the apparent length of the legs. Certain very large and massive animals, such as the rhi- noceroses and elephants, are un- guligrade in a modified sense; the foot is a heavy column, seem- ingly a part of the leg, and the weight is borne upon a great pad of elastic tissue, with the hoofs disposed around its periphery. A very peculiar mode of locomotion is exemplified by certain of the Edentata, in the forefoot of the existing Ant Bear (Myrmeco- phaga jubata) and in both ex- tremities of some of the later representatives of the extinct fground-sloths, or +Gravigrada. Here the weight is carried upon the outer edge of the foot, the palm and sole being turned in- ward. No term has been sug- gested for this very exceptional Fie. 43. — Left pes of Patagonian Deer (Hippocamelus bisulcus), showing the unguligrade gait. T., tibia. F., lower end of fibula (malleolar bone). Cal., calcaneum. As., astragalus. N.Cb., codssified cuboid and navicular. Mt. III, Mt. IV, cannon-bone, formed by the codssification of the third and fourth metatarsals. V., Rudimen- tary fifth digit. gait, which is a modified form of plantigradism. 92 LAND MAMMALS IN THE WESTERN HEMISPHERE II. Tue Trsts It was pointed out in Chapter II (p. 38) that very often the teeth are all that remains to us of extinct genera and species of mammals, and it may be further noted that the teeth are very characteristic and often suffice to fix the systematic position of a genus. Since, therefore, the teeth play such an uncom- monly important part as fossils and are so pre-eminently useful to the paleontologist, it is necessary to give some general account of them. Among the mammals the teeth display a very great variety of size and form in accordance with the manner in which they are used. Primarily, the function of the teeth is to seize and masticate food, and the kind of food habitually eaten by any animal is well indicated by the form of its teeth. The beasts of prey have teeth adapted for shearing flesh and crushing bones; plant-feeders have teeth fitted for cropping plants and triturating vegetable tissues; insect-eaters have teeth with numerous sharp-pointed cusps, or it may be, no teeth at all, swallowing without mastication the insects which they capture, etc. Among animals that have similar diet there is very great difference in the form and elaborateness of the grinding apparatus and it is often possible to follow out the steps of evolutionary change, by which, from simple beginnings, a high degree of complexity has been attained. In addition to the uses of the teeth as organs of mastication, they frequently serve as weapons of offence or defence. In the flesh-eaters which capture living prey they are formidable offensive weapons, and the fangs of the Lion or the Wolf are instances familiar to every:one; but the tusks of the elephants or the hippopotamuses have nothing to do with the taking of prey. Several Old World deer, which have no antlers or very small ones, possess scimitar-like upper tusks, with which they are able to defend themselves very effectually. In the lower vertebrates, such as reptiles and fishes, the SKELETON AND TEETH 93 number of teeth is usually indefinite and they continue to be shed and replaced, as needed, throughout life; but in each species of mammal, aside from abnormalities, the number is fixed and constant. Mammalian teeth are very generally divisible into four categories: (1) the incisors, or front teeth, which in the upper jaw are inserted in the premaxillary bones, (2) the canines, or eye-teeth, which are ee than one on each side Fig. 44. — Dentition of Wolf, left side. of each jaw, or four in all, (3) the —i.3, third incisor. C., canine. p.1, premolars, called in Man the bi- irae 4, fourth premolar. cuspids, the anterior grinding teeth which have predecessors in the milk-series and (4) the molars, the posterior grinding teeth which have no such pred- ecessors. It is customary and convenient to express the numbers and kinds of teeth of a given mammalian species by means of a “dental formula”; for example, in Man the formula is: v3, c1, p2, m3, X 2 =32; the reason for the multiplication by two is that the figures deal only with one side of the mouth and must be doubled to give the sum total. Just because, however, the two sides are alike, it is usual to take the doubling for granted. Written out in full, the formula means that Man has two incisors, one canine, two premolars and three molars on each side of each jaw, the horizontal line indicating the division between upper and lower teeth. The number of teeth is frequently not the same in the upper and lower jaws; for instance, the formula for the Sheep is :7 $, c$, p $, m3, X 2 = 32; the total is the same as in Man, but the arrangement is entirely different. The meaning is that in the Sheep there are no upper incisors or canines, but three incisors and a canine are present in each half of the lower jaw, with three premolars and three molars on each side above and below. The Dog gives still another formula: 73, c+, p4, mZ, x2 = 42. What is called the 94 LAND MAMMALS IN THE WESTERN HEMISPHERE typical formula for the higher terrestrial mammals above the grade of the marsupials and which is but rarely exceeded, is 7%, cl, p¢, m3, X 2 = 44, though most existing mammals have fewer teeth than this. Compared with the typical formula, the Dog has lost but two teeth, the third upper molar on each side, while Man and the Sheep have each lost twelve. As every one knows from his own experience, mammals normally have two sets of teeth, the first, temporary, or milk- dentition, in the young animal, and the second, or permanent dentition, in the adult. The milk-dentition, when fully developed, consists of incisors, canines and premolars, which usually agree in number, though often not in form, with the permanent teeth which replace them in the adult. The milk- teeth are frequently more conservative than the permanent ones and retain ancestral characters which have disappeared in the adult series, thus affording welcome information as to lines of descent and steps of evolutionary change. While there can be little doubt that the development of more than one dentition, or set of teeth, is the primitive condition among mammals and was derived by inheritance from their lower vertebrate ancestors, in which there was an indefinite succession of teeth; yet there are many mammals in which the milk- dentition is greatly reduced or altogether lost. In some, the milk-teeth are shed and replaced before birth, in others only the germs of the milk-teeth are formed and never cut the gum, while in others again all traces of the temporary series have vanished. This complete loss of the milk-teeth, like the pres- ence of a great number of simple and similar teeth in the dolphins and porpoises, or the total absence of teeth, as in the anteaters and whalebone whales, is a secondary and derivative condition, never a primitive one. The structure of mammalian teeth varies greatly, from the simplest slender cones to enormous and highly complicated apparatus, and, in order to comprehend the significance of these differences, we must look a little more closely into the be Bae SKELETON AND TEETH 95 materials of which the teeth are constructed and the manner in which those materials are combined. mammals and in many of the higher and more advanced ones (including Man) a tooth is composed of the crown, or portion which is exposed above the gum, and the roots,* one or more in number, by means of which the tooth is firmly inserted in the jaw-bone; the roots are at least partly formed before the tooth comes into use. Such a tooth is said to be short or low-crowned, or brachyodont. In many plant-feeders, such as_ horses, cattle, elephants, beavers, etc., the teeth continue to grow in height for a long time In all primitive Fic. 44a.— First upper molar, right side of Deer (Odocoileus). On the left, the masti- cating surface; heavy black line, enamel. On the right, external side, showing crown and roots. Brachyo- dont. and do not form roots until late in life, or perhaps not at all. Such teeth are said to be long- or high-crowned, or hypsodont, and in very many instances the development of brachyodont into Fic. 45. — First upper molar, left side, of a fos- sil horse (Equus sp.). side. showing two stages of wear. On the right, external On the left, the grinding surface, Heavy black line,enamel ; white, dentine ; shaded, cement. Hypsodont, roots not yet formed. hypsodont teeth may be fol- lowed through every step of the change. The advan- tage of the change is ob- vious in lengthening the animal’s life, especially in those which feed upon abra- sive substances, like grass, for the growth of the teeth long continues to make up for the loss through wear. Serious trouble has often been caused for captive el- ephants by giving them too soft food, so that the growth of the teeth is not properly balanced by abrasion. Still another category of teeth is 96 LAND MAMMALS IN THE WESTERN HEMISPHERE the rootless, which are of simple form, like those of an armadillo, and grow throughout life, never forming roots. The chisel-like, or scalpriform incisors of the ro- dents do not cease to grow while the animal lives; they are kept of constant length by continual use, and the arrangement of harder and softer tissue is such that the sharp edge is main- Fic. 46. — Dentition of Beaver (Castor tained ; through accident or canadensis). m.8&, last molar. p. 4, 7 i last premolar. 7.,scalpriform incisors; Malformation it sometimes hap- oo face black, dentine in vertical pens that the upper and lower teeth fail to meet, then the con- tinued growth causes them to form curved hoops in the mouth, locking the jaws and bringing death by starvation to the un- fortunate animal. The typical mammalian tooth is composed of three kinds of tissue, all differing in structure and hardness and called respectively (1) dentine, (2) enamel, (3) cement. (1) The dentine, or ivory, is the indispensable tissue of the tooth; the other kinds may be absent, but never the dentine. Chemically, it is like bone, but the microscope shows that its structure is quite different from that of true bone, being composed of an immense number of fine tubules, which radiate from the “‘pulp-cavity,”’ or chamber which contains the blood-vessels and nerves, these entering the tooth through the canals of the roots. The tubules of the dentine lodge excessively fine fibrillee of the nerve and that is why the cutting into a live tooth is so painful an operation. (2) The enamel, which is the hardest of all animal tissues, has a polished and shining appearance and is arranged in a mosaic of microscopic prisms, closely packed together, which in most mammals are solid, but in the marsupials, with some exceptions, are tubular. The enamel normally covers the entire crown of the tooth, but does not extend upon the roots, where its superior hardness SKELETON AND TEETH 97 would be of no advantage. In several instances, always as a secondary specialization, the enamel does not cover the whole crown, but is arranged in vertical bands, it may be on one side only, or at intervals around the tooth. The scalpriform incisors of the rodents, already alluded to, have the enamel band on the front face of the tooth; the softer dentine behind wears away more rapidly, keep- ing the cutting surface bevelled, like the edge of a chisel, while the hard enamel forms the sharp edge. In some instances the en- amel is absent altogether and the teeth are composed entirely of ' dentine, as in the elephant tusk. Gee a In all the Edentata, such as phas mazimus). Enamel, heavy sloths and armadillos, both liv- Heeler wintey (Dement, ing and extinct, that have any teeth at all, the teeth have no enamel, but in some of the fossil forms the place of the missing enamel is taken by a harder dentine and thus the effect of differential hardness is secured. (3) The cement is simply bone, both chemically and in microscopic structure; it is not quite so hard as dentine, but it is less affected by the fluids of the mouth and the juices of the food. In the brachyodont or low-crowned tooth, such as a human molar, the cement merely forms a sheath over the roots and does not appear upon the crown, but in many hypsodont teeth, those of horses and elephants, for example, the cement completely encases the entire tooth in a thick layer, filling up all the depressions and irregularities of the enamel surface and making a freshly erupted and unworn tooth look like a shapeless lump. When the cement and the enamel covering are partially worn through, the masticating surface is made up of three distinct substances, each having a dif- ferent degree of hardness and thus, through unequal wear, H 98 LAND MAMMALS IN THE WESTERN HEMISPHERE the grinding surface is always kept rough and therefore efficient. Not all hypsodont teeth have the cement covering, but in such teeth the differing degrees of hardness of enamel and dentine suffice to keep a rough surface, though not so effectively. CHAPTER V THE GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS IN CENOZOIC TIMES I. Tertiary Prriop In the interior regions of western North America the transi- tion from the Mesozoic to the Cenozoic was so gradual that there is great difficulty in drawing the line between them and therefore, as might be expected, there is much difference of opinion as to just where that line should be drawn. From one point of view, the matter is of no great consequence ; but from another, it is of the utmost importance, for, unless the events in different continents can be approximately syn- chronized, it will often prove a hopeless undertaking to trace the course of migration of the various mammalian groups and determine their place of origin and primary home. Until a definitive answer can be given to the question as to when the Cenozoic era began, many significant points must be left in doubt, and much remains to be done in the geology of the Far West before that definitive solution can be reached. 1. Paleocene Epoch -So far as North America is concerned, the best available evidence points to the conclusion that we should regard the Fort Union, Puerco and Torrejon as the most ancient of the Cenozoic formations (see Table, p. 17), though retaining so many features of Mesozoic life that a separate division of the Tertiary, the Paleocene epoch, is made for them. Such asepa- ration is not the common practice in this country, where it is more usual to employ the terms ‘‘ Lowest”’ or “‘ Basal” Eocene. 99 100 LAND MAMMALS IN THE WESTERN HEMISPHERE In my judgment, however, the balance of advantage is in favour of giving to this so-called Basal Eocene a rank equivalent to that of the four other universally recognized and admitted epochs of the Tertiary period. No marine rocks of Paleocene date have yet been found in North America, which indicates that the continent’ was at least as extensive as it is now. The very scanty dévelopment of deposits representing this epoch in Europe renders the comparison with the fossils of the Old World unsatisfactory and hence leads to uncertainty, when it is attempted to determine the land-connections of the time. During the Mesozoic era the shallow Bering Sea had repeatedly been elevated into a land joining North America with Asia and had as often been depressed, so as to separate the conti- nents and allow the waters of the Arctic Ocean to mingle with those of the Pacific. A like alternation of junction and separa- tion went on during the Tertiary and Quaternary periods and, by a comparison of the fossil mammals of Europe and America for any particular division of geological time, it is almost always feasible to say whether the two continents were con- nected, or altogether separated. This statement does not imply that the proportion of common elements in the two faunas during epochs of continental connection was a con- stant one at all times, for that was by no means true. Mere land-connections or separations are not the only factors which limit the spread of terrestrial animals; if they were, the com- munity of forms between North and South America would be much greater than it actually is. Climatic barriers are of almost equal importance in determining animal distribution, and changes of climate may greatly alter the conditions of migration between connected continents. As the connections between North America and the Old World were probably in high latitudes, where the seas are narrow, changes of climate produced a greater effect upon migration than they could have done had the land-bridges been in the tropical or warm tem- perate zones. That these vicissitudes of climate really did GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 101 occur and are not mere guesses to bolster up a tottering hy- pothesis, there is abundant evidence to prove. In the Paleocene, or most ancient epoch of the Tertiary period, the geographical condition of North America was ap- proximately as follows: The continent had attained nearly its modern outlines and on the Atlantic and Pacific coasts probably extended farther seaward than it does to-day. Florida, however, and perhaps a narrow strip of the northern Gulf coast were still submerged, the Gulf of Mexico opening broadly into the Atlantic. It is very probable that the continent was connected with the Old World by a land occupying the site of Bering Sea and perhaps also by way of Greenland and the North Atlantic; and there is some evidence, though not al- together convincing, that it was also joined to South America. The great mountain ranges were largely what they now are, though subsequent upheavals greatly modified the Rocky Mountains, Sierra Nevada and the ranges of the Pacific coast, while the lofty St. Elias Alps of Alaska were not in existence. The region of high plateaus, between the Rockies and the Sierras, was much less elevated than it is now. The Appala- chians, which were of far more ancient date than the western ranges, had been worn down by ages of weathering and stream- erosion into a low-lying, almost featureless plain, with some scattered peaks rising from it here and there, of which the moun- tains of western North Carolina were the highest. In general, it may be said that while the average height of the continent above the sea-level may have been as great or greater than at present, yet the inequalities of surface appear to have been less marked, and both along the Atlantic coast and in the in- terior were vast stretches of plains. The Paleocene formations of the western interior are of non-marine or continental origin. In northwestern New Mexico is the typical area of the Puerco and Torrejon, a series of beds 800 to 1000 feet in thickness and for the most part quite barren of fossils, but there are two horizons, one near the top 102 LAND MAMMALS IN THE WESTERN HEMISPHERE and the other near the bottom of the series, which have yielded a very considerable number of fossil mammals, and of these the lower is the Puerco, the upper the Torrejon. The Fort Union is quite different in character and is composed of great areas of sandstone and clay rocks, with a maximum thickness of 2000 feet, in eastern Wyoming, South Dakota, Montana and the adjoining parts of Canada. The modes of formation of these beds have not yet been fully determined; that they may have been partly laid down in shallow lakes is indicated by the masses of fresh-water shells in certain localities. In others are preserved multitudes of leaves, which have given a very full conception of the plants of the time, and great swamps and bogs have left the traces of their presence in beds of lignite, or imperfectly formed coal. Deposits made on the flood- plains of rivers and wind accumulations are probably also represented. ‘‘Vast stretches of subtropical and more hardy trees were interspersed with swamps where the vegetation was rank and accumulated rapidly enough to form great beds of lignite. Here were bogs in which bog iron was formed. Amid the glades of these forests there wandered swamp turtles, alli- gators, and large lizards of the characteristic genus Champ- sosaurus’’ (Osborn, p. 100). Fort Union mammals are relatively rare and most of those that have been found are very fragmentary; they are amply sufficient, however, to demonstrate the Paleocene date of the beds and to make it probable that they include both the Puerco and the Torrejon faunas. The climate, as shown by the plants, was much milder and more uniform than that of the Recent epoch, though some in- dication of climatic zones may already be noted. The vegeta- tion was essentially modern in character ; nearly all our modern types of forest-trees, such as willows, poplars, sycamores, oaks, elms, maples, walnuts and many others, were abundantly represented in the vast forests which would seem to have covered nearly the entire continent from ocean to ocean and extended GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 103 north into Alaska and Greenland, where no such vegetation is possible under, present conditions. Numerous conifers were mingled with the deciduous trees, but we do not find ex- clusively coniferous forests. Palms, though not extending into Greenland, flourished magnificently far to the north of their present range. On the other hand, the Paleocene flora of England points to a merely temperate climate, while that of the succeeding Eocene was subtropical. South America. — Nothing is definitely known concerning the condition of Central America and the West Indies and very little as to South America. As no marine rocks of Paleocene date have been found in any of these regions, it may be inferred that all the existingland areas were then above the sea, and there is some evidence that South America was much more extended in certain directions than now. From the character and dis- tribution of modern plants, fresh-water fishes, land and fresh- water shells, there is strong reason to believe that in late Mesozoic times a land-bridge connected Brazil with equatorial Africa and this connection may have continued into the Pale- ocene, though it is only fair to observe that some highly com- petent authorities deny the reality of this bridge. There is also evidence, though incomplete, of a connection between South America and Australia by way of the Antarctic continent, and it is clear that that polar region could not have had the’ rigorous climate of the present time. In the upper part of the Cretaceous, the last of the Mesozoic periods, there was a possibility of migration, however indirect, between every continent and every other, for the huge land reptiles called Dinosaurs have been found in the non-marine Cretaceous rocks of every continent, which could not have been the case, had any of the great land areas been isolated. There is no known reason to assume that the land-bridges were essentially different in the Paleocene. 104 LAND MAMMALS IN THE WESTERN HEMISPHERE 2. Eocene Epoch North America. — The Eocene witnessed quite extensive geographical changes, though but little is known of it in Central or South America, or the West Indies. Along the Atlantic and Gulf coasts of the United States there was an extensive submergence of the coastal plain, the sea covering the southern half of New Jersey and extending thence to the southwestward in an ever broadening band, through the South Atlantic and Gulf states. Northern Florida was under water and the Gulf extended as a narrow sound, known as the “‘ Mississippi Em- bayment,” up the valley of that river to southern Illinois and westward into Texas. The Embayment was present in the Cretaceous and again in the Eocene, but it is not known whether it persisted through the Paleocene; probably it did not, as the whole Atlantic coast region appears to have stood at a higher level then than now. While the condition of Mexico and Central America during the Eocene is not known in any save the vaguest manner, it is evident that there was then a broad communication between the Atlantic and the Pacific, completely severing North and South America, though the place of this transverse sea has not been fixed. On the Pacific side, a long, narrow arm of the sea occupied what is now the great valley of California, extending north into Oregon and Washington. It will be noted that in North America the Eocene sea was almost confined to the neighbourhood of the present coast-lines, nowhere penetrating very far inland, except in the Mississippi Embayment, and thus differing widely from the condition of Europe at that epoch, where much of what is now land was submerged. The greatly expanded Mediter- ranean covered most of southern Europe, where the great mountain ranges, the Pyrenees, Alps, etc., had not yet been formed. Very important, from the point of view of American geography, is the fact that Europe was completely separated from Asia by a narrow strait or sea, which ran down the eastern GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 105 m2 - Fic. 48. — Map of North America during the Eocene epoch. The present limits of the continent are shown in outline; white areas = land; horizontal lines = sea; dotted areas = non-marine deposits; black circles with white dots = active volcanoes. (After Schuchert.) 106 LAND MAMMALS IN THE WESTERN HEMISPHERE side of the Ural Mountains from the Arctic Ocean and joined the enlarged Mediterranean. During the existence of this Ural Sea any land connection of North America with Europe must necessarily have been by means of a North Atlantic bridge, or by one across the Arctic Sea, since communication with Asia by way of Alaska would not have reached eastern Europe. Any such general statement of geographical conditions during the Eocene as the foregoing sketch, cannot but be to some extent misleading, because it brings together, as con- temporary, arrangements which were, in some cases at least, separated by considerable intervals of time and which were subject to continual change. Along nearly all coasts the posi- tion of the sea was quite different in the latter part of the epoch from what it had been in the earlier portion. On the north side of the Gulf of Mexico, for example, the sea retreated from time to time, and the successive divisions of the Eocene rocks are so arranged that the later ones are farther to the south. Limitations of space, however, forbid’ the attempt to follow out these minor changes. In the western interior are found extensive non-marine or continental deposits of Eocene date, which must be con- sidered more in detail, because of the highly important bearing which they have upon mammalian history. With the excep- tion of a few small areas in Colorado, these deposits are all situated in the plateau region west of the Rocky Mountains, and were made of the débris of older rocks washed down by rain and rivers and deposited in broad basins. Some of them are the sediments of shallow or temporary lakes, and one series, at least, is made up of volcanic ash and dust showered upon the land, or into water of no great depth. The oldest of these Eocene stages, known. as the Wasatch (see Table, p. 17) covers a very large region, though in a discontinuous manner; the principal area begins in New Mexico, where it lies over the Torrejon, of the Paleocene, and extends far to the north through. GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 107 Fig. 49. — Bad Lands of the lower Eocene, Wasatch stage. Big Horn Basin, Wyo. (Photograph by Sinclair.) 108 LAND MAMMALS IN THE WESTERN HEMISPHERE western Colorado and eastern Utah to the Uinta Mountains, around the eastern end of which it passes in a narrow band and then expands again over southwestern Wyoming. A second area is in the Big Horn Basin of northwestern Wyoming and southern Montana, and probably two small areas in southern Colorado are of the same date. The Wasatch beds are richly fossiliferous and have yielded a most interesting and important series of mammals, which were far more advanced than those of the Paleocene; and, at first sight, the student is tempted to believe that they must be of very much later date. A more critical examination shows that this appearance of a great lapse of time between the Paleocene and the Wasatch is decep- tive; the more advanced and characteristic of the Wasatch mammals were obviously not the descendants of ancéstors in the. North American Paleocene, but were altogether new- comers to this continent, immigrants from some region which cannot yet be identified. On the other hand, a considerable number of the old, indigenous types still persisted, and these, when compared with their Paleocene ancestors, are found not to have changed so much as to require a very great length of time, geologically speaking, for the degree of development involved. This is the earliest recorded one of the great waves of mammalian migration which invaded North America down almost to our own time. The same wave of migration extended to Europe, and that there was a broad and easy way of communication between that continent and North America is plain, for the similarity between the Wasatch mammals and those of the corresponding formation in France, the Sparnacian, is remarkably close. At no subsequent time were the mammalian faunas of North America and Europe so nearly identical as during the Wasatch- Sparnacian age, which is especially remarkable when the dis- crepancy is noted between the vast stretches of the Wasatch (150,000 square miles) and the very limited areas in France. If, as is probable, the Ural Sea was in existence at that time, GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 109 the land-connection with Europe must have been across the North Atlantic, most likely from Greenland eastward. At the present time a land-bridge in such high latitudes would be of little service in bringing about a similarity of mammals in the two continents, for the severity of the Arctic climate would be as effective a barrier against the intermigration of all save the Arctic mammals as the ocean itself; but in the mild and genial Eocene climate the latitude of the bridge was of small conse- quence. The second of the Eocene stages, the Wind River — Green River, is found in two very different phases. The Wind River phase occupies the basin of that stream, north of the Wind River Mountains in central Wyoming, and in the Big Horn Basin of the same state it very extensively overlies the Wasatch, and in this phase the sediments are very like those of the latter, flood-plain and wind accumulations. A widely distant area of this stage occurs in the Huerfano Cafion in Colorado. The Wind River beds contain numerous mammals which were clearly sequential to those of the Wasatch, of which they were the more or less modified descendants. With two possible exceptions, there were no new immigrants and the connection with the Old World may have been already severed, as it as- suredly was in the succeeding age, the Bridger, though diver- gent development had not yet had time to produce the very striking differences in the mammals of North America from those of Europe, which characterized the Bridger. The Green River phase is a thick body of finely laminated ‘‘naper shales,’ which seem to have been deposited in a very shallow lake and occupy some 5000 square miles of the Green River valley in southern Wyoming and northern Utah, where they overlie the Wasatch, just as do the Wind River beds in the Big Horn Basin. These fine-grained and thinly laminated shales have preserved, often in beautiful perfection, countless remains of plants, insects and fishes, but no traces of mammals, other than footprints, have been found. 110 LAND MAMMALS IN THE WESTERN HEMISPHERE The third of the Eocene stages of the interior is the Bridger of southern Wyoming and northeastern Utah, where it lies upon the Green River shales, but overlaps these shales both eastward and westward, extending out upon the Wasatch. The Bridger beds are largely made up of volcanic ash and dust deposited partly upon the land and partly in shallow or tem- porary lakes. The frequency with which the remains of fishes, crocodiles and fresh-water shells are found indicates deposition . in water, and the large crystals of gypsum which are abundant in certain localities show that the water became salt, at least occasionally. From the immense mass of volcanic débris, it is evident that volcanic activity broke out at this time on a much greater scale than had been known in that region since the Cretaceous period. Two different horizons, or substages, are distinguishable in the Bridger, lower and upper, each of which has its distinct mammalian fauna, though the two are very closely allied. Their difference from the contemporary mammals of Europe is very great, hardly any genera being common to the two continents. So striking a difference in- dubitably points to a severance of the land-connection, a sever- ance which, as was shown above, probably took place during the Wind River stage, for its effects would not be immediately apparent; time would be required for the operation of diver- gent evolution, the fauna of each continent developing along its own lines, to make itself so strongly felt. Had the connec- tion never been renewed, North America, on the one hand, and ‘Eurasia on the other, would to-day be utterly different from the zoological point of view, instead of containing, as they do, a great many identical or closely similar animals of all classes, a likeness due to subsequent migrations. The fourth and last of the stages referred to the Eocene is the Uinta, the geological position of which is the subject of much debate; almost as good reasons can be brought forward for placing it in the Oligocene as in the Eocene, so nearly is it on the boundary line between those two epochs. GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 111 The Uinta is found in the Green River valley of northeasterri Utah and northwestern Colorado, where it lies upon the upper Bridger and is the latest of the important Tertiary formations to be found in the plateau region west of the Rocky Mountains. It is probable that the separation of North America from the Old World still continued, for, as a whole, the Uinta fauna is totally different from that of the upper Eocene of Europe. There were, however, a few doubtful forms, which may prove to be the outposts of a renewed invasion. The Eocene climate was decidedly warmer than the present one, and subtropical conditions extended over the whole United States and perhaps far into Canada. On the other hand, signs of increasing aridity in the western part of the continent are not wanting, and that must have resulted in a great shrink- age of the forests and increase of the open plains. The vegeta- tion was essentially the same as in the Paleocene, when it had already attained a modern character, the differences from the present being chiefly in regard to geographical distribution. Large palms were then flourishing in Wyoming and Idaho, and another indication of a warm climate is furnished by the. large crocodiles which abounded in all of the Eocene stages. So far as North America was concerned, the Eocene epoch was brought to a close by extensive movements of the earth’s crust, which more or less affected the entire continent and were registered both on the sea-coasts and in the mountain ranges of the interior. Upheaval added a narrow belt of land along the Atlantic and Gulf coasts and the Mississippi Embayment was nearly closed. On the Pacific side the sea withdrew from the great valley of California and Oregon, and in the interior the plateau region was elevated by a great disturbance, which also increased the height of the western mountains. Our knowledge of Eocene land-mammals in North America is almost wholly derived from the formations of the western United States, but it may be inferred from the uniform climatic conditions that there were no very great geographical dif- 112 LAND MAMMALS IN THE WESTERN HEMISPHERE ferences among the animals. This inference is confirmed by the discovery of a Bridger genus, very fragmentary but identi- fiable, in the marine Eocene of New Jersey. South America. — No Eocene rocks, marine or continental, are known in the West Indies or Central America, but the latter region has been so imperfectly explored that no great impor- tance can be attached to this fact. North and South America were separated completely, as is proved by the entire dis- similarity of their mammalian faunas, but the position of the transverse sea or strait cannot be determined. There is much reason to believe that the Greater Antilles were connected into a single large land, which has been called ‘‘Antillia”’ and may have been joined to the mainland of Central America. Certain marine rocks in Patagonia and Chili have been re- ferred to the Eocene by South American geologists, but the reference is almost certainly erroneous, the rocks in question being much more probably Miocene. The Andes, probably throughout their length and certainly in their southern half, stood at a much lower level than they do now, and, no doubt, were rising, either slowly and steadily, or periodically and more rapidly, throughout the whole Tertiary period. At all events, their present height in the south is due to movements in the Pliocene or later. Continental deposits of Eocene date have been discovered only in northern Patagonia (Casa Mayor) where they occupy depressions in the worn and eroded sur- faces of the Cretaceous rocks; the mode of their formation has not been carefully studied. There is great uncertainty as to the status of the land- bridge which, it is believed, in the Cretaceous period connected South America with Africa. Some of the evidence goes to show that the connection persisted throughout the Eocene epoch, but the testimony is that of fragmentary and therefore imperfectly understood fossils and is farfrom being unequivocal. The connection with Antarctica probably continued. GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 113 3. Oligocene Epoch North America. — The Oligocene, or third of the Tertiary epochs, was a time of great significance in the history of the American mammals and of great geographical changes in the West Indian and Central American regions, but in North America proper the changes were not so widespread. On the Atlantic coast the marine Oligocene is but scantily displayed except in the Florida peninsula, where it is found in a thick- ness of some 2000 feet, but it is well developed along the north shore of the Gulf of Mexico, where the coast-line followed that of the Eocene, only a little farther to the south, marking the retreat of the sea at the end of the Eocene. The Gulf Stream entered the Atlantic over the site of northern Florida and flowed northward nearer the coast than it does to-day, in consequence of which warm-water conditions extended far to the north and West Indian shells flourished on the New Jersey coast. In the middle Oligocene part of northern Florida was elevated into an island and the water over much of the remainder of the peninsula became shallower, but this did not greatly alter the course of the Gulf Stream. The Pacific encroached upon the western shore of Oregon and British Columbia and very extensively upon that of Alaska, where strata no less than 10,000 feet thick are assigned to this epoch. In the western interior Oligocene formations are among the most important and widely spread of the continental Tertiaries and are divisible into two principal stages and each of these again into three substages. Of these, the older or White River stage covers a vast region in northeastern Colo- rado, western Nebraska, eastern Wyoming and southern South Dakota, with separate areas in the Black Hills, North Dakota and the Northwest Territory of Canada. The de- posits are believed to be chiefly of fluviatile origin, and many of the ancient stream-channels, some of great size, may still I 114 LAND MAMMALS IN THE WESTERN HEMISPHERE il Fie. 50.— Map of North America in the upper Oligocene. Explanation ‘as in Fig. 48. (After Schuchert.) GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 115 be traced, filled with the consolidated sands and gravels of the old rivers. The country was very flat and the divides between the streams very low, so that in seasons of flood great regions were converted into shallow, temporary lakes, in which were deposited the finer silt and mud, but were dry for most of the year. The volcanic activity which had gone on so impressively in the Bridger Eocene was renewed in White River times, as is proved by thick beds of pure volcanic ash, which must have been carried long distances by the wind, for they occur far from any volcanic vent. The White River fauna is more completely known than that of any other Tertiary formation of this continent. The first discovery of these fossils was made more than 70 years ago and since then oft-repeated expeditions have brought to light an astonishing number and variety of mammals. Not only are these beds remarkable for the immense quantity of material which they have yielded, but also for its complete- ness and beauty of preservation, a most unusual number of skeletons having been obtained. The mammals demonstrate that the land-connection with the Old World had been re- established, for many European genera, which could not have been derived from an American ancestry, are found in the White River beds. At the same time, there was no such proportion of forms common to both continents as there had been in the Wasatch-Sparnacian stage of the lower Eocene, each having many genera and even families which did not extend their range into the other. The reason for this remark- able and, at first sight, inexplicable difference between the lower Eocene and the lower Oligocene is probably to be found in climatic changes, in consequence of which relatively fewer genera were able to take advantage of the reopened connection, which lay far to the north. The White River mammals, like those of the Recent epoch, are thus divisible into two groups or elements, one set indigenous and descended from ancestors which are found in the American Eocene, and the other com- \ 116 LAND MAMMALS IN THE WESTERN HEMISPHERE posed of late immigrants from the Old World. Migrants from North America likewise made their way to Europe. The upper continental Oligocene of the interior has re- ceived the peculiar appellation of the John Day, from the river of that name in eastern Oregon, a large part of which was buried to a depth of 3000 or 4000 feet in stratified volcanic ash and tuff. This great mass of finely divided volcanic material was derived from the craters of the Cascade Moun- tains to the westward; a long-continued series of eruptions would be needed to form such thick accumulations at such a distance from the sources of supply. The John Day evi- dently succeeded the White River very closely in time, but is marked by the disappearance of almost all the European migrants. This fact, together with the absence of any new immigrant genera, is evidence that the connection had again been broken and it was not renewed until after a considerable lapse of time. There are many reasons for believing that the Oligocene climate marked the beginning of the very long and gradual process of refrigeration which culminated in the glacial con- ditions of the Pleistocene epoch, but the change was slight and probably chiefly affected the far north. The climate, however, remained notably warmer than the present one of the same extra-tropical latitudes, as is abundantly proved by the fossils. The Atlantic coast,.as noted above, was bathed in warm waters, the plants of the Alaskan Oligocene point to temperate conditions and the vegetation of Europe was subtropical, palms growing in the north of Germany. The change which was distinctly to be noted in the Great Plains region of North America was probably due rather to the ele- vation.and increased altitude of the western interior than to general climatic alteration. Crocodiles are very rare indeed in the White River beds and those that have been found all belong to dwarf species, while none are known from the John Day. Unfortunately, hardly anything has been ascertained GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 117 concerning the Oligocene vegetation of the region, but the reptiles indicate diminished warmth. South America. —Marine Oligocene strata have great extent around the Gulf of Mexico and the Caribbean Sea, and the distribution of these shows that Antillia was broken up by great submergences, the islands of the Greater Antilles being much smaller than they are to-day. The greater part of Central America and the Isthmus were under water, a broad sea, broken only by scattered islands, separating North and South America. Very little is known of the Oligocene in the latter continent save a non-marine formation in northern Patagonia, the Deseado stage (or Pyrotherium Beds), which, like the Eocene of the same region, occupies depressions in the worn and irregular surface of the Cretaceous rocks. The attribution of the Deseado to the Oligocene is open to some doubt, because of the entire absence in its mammalian fauna of any elements which are also found in the northern hemi- sphere. Hence, there are no means of direct comparison. 4. Miocene Epoch North America. — The Atlantic and Gulf coasts, which had been raised in the Oligocene, were again depressed, almost restoring the Eocene coast-line, the chief differences being the presence of the Florida islands and the nearly complete closing of the Mississippi Embayment. There was a remark- able change in the marine fauna from that of Oligocene times ; a cool current flowed southward along the coast and entered the Gulf of Mexico through the strait between the Florida island and the mainland, bringing the northern animals with it and driving out the tropical forms. This complete faunal change, which might fairly be called a revolution, was the most sudden and striking in the Tertiary history of the continent. On the Pacific coast also there was a depression, which caused a renewed transgression of the sea. The Coast Range formed a chain of reefs and islands in the Miocene sea, which 118 LAND MAMMALS IN THE WESTERN HEMISPHERE again filled the great valley of California, except in the northern part of what is now the Sacramento Valley, where there was an accumulation of continental deposits. The immense thick- ness (5000 to 7000 feet) of the California Miocene is largely made up of. volcanic material, which testifies to the great activity of the vents. In the Sierras, the height of which was increased in the upper Miocene, there was also a great display of vulcanism, recorded in the lava-flows and tuffs of the time. In the region of Lower California and northwestern Mexico considerable changes of the coast-line took place during the Miocene; in the earlier half of the epoch the Gulf of Cali- fornia was much shorter and narrower than it is to-day and the peninsula was broadly united with the mainland to the east as well as to the north. A wide submergence marked the upper Miocene, reducing the peninsula to a long, narrow island and enlarging the gulf considerably beyond its present limits, flooding an extensive area in northwestern Mexico and sending a small bay into southeastern California. There were great disturbances in the course of the epoch, for in the Santa Cruz Mountains near San Francisco the lower Miocene strata were crumpled into folds, before those of the upper Miocene were deposited upon them. British Columbia, Washington and Oregon were invaded by the sea, which extended up the valley of the Columbia River and its southern tributary, the Willamette, though here the beds are far thinner than those of California. Much of Alaska, both on the north and west coasts and in the valley of the Yukon, was submerged, and the land-connection with Asia appears to have been broken. This is made probable not only by the submergence of the Alaskan coast, but also by the fact that the marine animals of the Cali- fornia coasts and shoal waters, which could not migrate across the ocean, were quite unlike the contemporary forms of the eastern Asiatic shore, which would hardly have been the case, had a continuous coast-line united the two continents. On the other hand, there was a renewed connection with Europe, as GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 119 Fie. 51.— Map of North America in the upper Miocene. Explanation as in Fig. 48. (Modified from Schuchert.) 120 LAND MAMMALS IN THE WESTERN HEMISPHERE is shown by the appearance of Old World land-mammals, beginning scantily in the lower and becoming numerous in the middle Miocene. This connection, it will be remembered, had been interrupted during the upper Oligocene. Many students of the problem have maintained that the land-bridge was by way of the West Indies and the Mediterranean lands, but such a bridge would not account for the facts of mammalian distribution, which would seem to require its location in the far north. Several distinct lines of evidence go to prove that the junction of the Americas dates from the Miocene, possibly from the beginning of it. The absence of Atlantic species from the Pacific Miocene is an indication that the passage from ocean to ocean had been closed, and this is confirmed by the geology of the Central American and Isthmian region. In the middle Miocene of Oregon and Nebraska have been found remains, which are unfortunately too incomplete for altogether convincing identification, but which can be inter- preted only as belonging to the extinct and most characteristi- cally South American group of edentates, the tground-sloths or {Gravigrada; if this reference is correct, the fact of the junc- tion cannot be questioned. Continental deposits of Miocene date, chiefly accumula- tions made by rivers and the wind, cover vast areas of the west- ern interior, though but rarely to any considerable depth. These have been divided into several stages and have received various names; the lower Miocene, known as the Arikaree, Harrison or Rosebud, overlies the White River in South Dakota, western Nebraska and eastern Wyoming, with smaller areas in Montana and Colorado. In the deposits of this stage there are no mammals of indisputably Old World type, though a few which I consider to be such are a probable indication of re- newed connection with Europe. The middle Miocene is found typically in central Montana, where it is called the t Extinct. GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 121 Deep River (or Smith River) stage, but occurs also in numerous small, scattered and widely separated areas in Oregon, Wyoming, Colorado and Texas, with local names in these different states. It is most likely that these middle Miocene formations are not strictly contemporaneous in the geological sense, but rather form a closely connected and successive series. The mammals of the Deep River stage leave no doubt that the way of migration from the Old World was again open. The Loup Fork, or upper Miocene, itself susceptible of further subdivision, is by far the most extensive of the Miocene formations and covers much of the Great Plains region, in separate areas, from South Dakota far into Mexico. Perhaps also referable to the upper Miocene is a small, but very inter- esting formation, the Florissant, which is in the South Park of Colorado; it was made by very fine volcanic material showered into a small and shallow lake. The finely laminated papery shales of the Florissant have preserved countless plants and insects and many fishes, and these throw very welcome light upon the vegetation and climatic conditions of the epoch and afford an interesting contrast to the fauna and flora of the Green River shales of the lower or middle Eocene. That the Florissant shales are Miocene, no one questions, but: their isolated position and the fact that they have yielded no mammals make it somewhat doubtful whether they belong in the middle or later part of the epoch. In the western portion of the continent vulcanism was dis- played on a grand scale during the Miocene. Mention has already been made of the quantity of volcanic material in the marine Miocene of California and also in the lavas and tuffs of the Sierras. The magnificent cones, such as Mts. Hood and Tacoma, which are the glory of the Cascades, are believed to date from this time. In Idaho and eastern Oregon and. Washington are the immense lava-fields of the Columbia ’ River, which are, partly at least, of Miocene date and were chiefly extruded through great fissures, the lava flooding the 122 LAND MAMMALS IN THE WESTERN HEMISPHERE valleys and plains in a fiery sea of molten rock. In Oregon these lavas rest upon the upper Oligocene (John Day stage) and middle Miocene beds are deposited upon them, which fixes their date sufficiently. In the Yellowstone Park was piled up a huge mass of voleanic products, lava-flows and beds of ash and tuff, to a thickness of several thousand feet. The ash-beds have preserved the petrified forests, with their tree- trunks still standing one above another; one locality in the Park shows seven such forests, each‘one killed and buried by a great discharge of ash and then a new forest established and growing upon the surface of the accumulation. In the tuffs are leaf-impressions which permit identification of the plants. ; In the latter part of the Miocene and at its close there were important crustal movements, which affected all the Pacific coast mountain ranges, though this epoch was.no such time of mountain making in America as it was in the Old World. The principal elevation of the Coast Range“in., California and Oregon was due to these movements, and the ‘Sierras and the plateaus of Utah and Arizona were increased’ in height. On the Atlantic side the Florida island was joined to the mainland and thus the present shape of the continent was almsést“exactly ~ gained. nee” The Miocene climate of North America, as indicated by the plants of Florissant, the Yellowstone Park and Oregon, was distinctly milder than at present, a southern vegetation of warm-temperate character extending to Montana and perhaps much farther north, but it was not so warm as it had been in the Eocene, and palms are not found in any of the localities mentioned, nor do crocodiles occur in any of the northern Miocene formations. In Europe the climate ef the early Miocene was considerably warmer than in North America, the vegetation of central and western Europe being very much like that of modern India. This difference between the two ~ sides of the Atlantic was probably due, in large part, to the GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 123 manner in which Europe was broken and intersected by arms and gulfs of the warm southern sea. In the latter half of the epoch, however, the climate became colder, the subtropical flora giving way to a distinctly temperate one. . South America. — In Central America, where marine Oli- gocene beds are of great extent, no Miocene is known, and on the Isthmus Oligocene is the latest marine formation, except a narrow fringe of Pleistocene on the Caribbean coast. These facts and others already cited lead to the conclusion that in the Miocene the connection of the Americas was complete and that the Isthmus was considerably broader than at present, extending nearly to Jamaica. The condition of the Greater Antilles is but vaguely understood, but they were involved in the general elevation of the Caribbean region and were at least as large as they are now and may have been considerably larger, and Cuba was perhaps joined. to Central America, as Hayti probably was. In South America proper nearly the whole of Patagonia was submergéd- “by the transgression of a shallow, epiconti- nental sea,#n which were accumulated the beds of the Pata- gonian stage, containing an exceedingly rich and varied as- sembl ei marine fossils, an assemblage which has very little in common withthe contemporary formations of the northern hemisphere. It is this lack of elements common to the northern faunas which has led to the long debate concerning the geo- logical date of the Patagonian formation, the South American geologists very generally referring it to the Eocene. How- ever, the occurrence of genera of Cetaceans (whales and dol- phins), which are also found in the Miocene of Maryland and Virginia, is very strong evidence that the proper date of the Patagonian is Miocene. A continuous coast-line, or at least an unbroken continuity of shoal-water conditions, seems neces- sary to account for the similarity of the Patagonian fossils with those of New Zealand and Australia, and that this con- nection was by way of the Antarctic continent is indicated by 124 LAND MAMMALS IN THE WESTERN HEMISPHERE the occurrence of similar fossils in the South Shetland Islands, an Antarctic group. On the Chilian coast the Navidad forma- tion, which is believed to be approximately contemporaneous with the Patagonian, has so different a fauna as to point to some kind of a barrier between the Atlantic and the Pacific, and this barrier, Dr. von Ihering holds, was the land-extension from South America to Antarctica. After some oscillations of retreat and advance, the sea with- drew from Patagonia, and the terrestrial accumulations of the Santa Cruz stage were formed. These beds are partly com- posed: of river-deposits, but chiefly of more or less consolidated volcanic ash or tuff, and have yielded a surprising number of beautifully preserved mammals. No other assemblage of South American Tertiary Mammalia is so well known and understood as the Santa Cruz fauna, and the very large number of all but complete skeletons which have been found strongly suggests that many of the animals were buried alive in the showers of volcanic ash. The Santa Cruz fauna is completely and radically different from any of the North American as- semblages, and at that time no immigrant from the north had penetrated so far as Patagonia. In the upper Miocene the Andes stood at a much lower level than they do now; fossil plants, some of them collected at a great height in the mountains, are the remains of a luxuri- ant and purely tropical flora nearly identical with the vegeta- tion of the modern forests of Bolivia and Brazil. Such a vegetation could not exist at the altitudes where the fossils occur and these demonstrate a great elevation of the mountains since those leaves were embedded. The same mild climatic conditions which prevailed in the northern hemisphere during the Miocene must also have characterized Patagonia, sub- tropical shells extending far to the south of their present range. Whatever may have been true of the land-bridge connecting South America with Africa during the early Tertiary epochs, GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 125 it must have been submerged in the Miocene, otherwise there would not have been the open pathway for the Cetacea of Patagonia to reach the Atlantic coast of North America and vice versa. 5. Pliocene Epoch North America. — The Pliocene of North America is not nearly so well displayed or so satisfactorily known as the pre- ceding Tertiary epochs, and only of comparatively late years has it been recognized at all upon the Atlantic coast. The Atlantic and Gulf shores had very nearly their present outlines, but with some notable differences. It would seem that the northeastern portion of the continent stood at a higher level than it does now, north Greenland being joined with the islands of the Arctic archipelago and Newfoundland with Labrador, the Gulf of St. Lawrence then being land. From Nova Scotia to southern New Jersey the coast-line was many miles to the east and south of its present position, but the sea encroached here and there upon the shores of Virginia, the Carolinas and Georgia, and southern Florida was mostly under water, as was also a narrow strip of the Gulf coast from Florida to Texas and along the east of Mexico. ‘On the Pacific side of the con- tinent the marine Pliocene is far thicker and more important than on the east coast and in California is largely made up of volcanic materials. Quite extensive disturbances in this region had marked the close of the Miocene, the strata of which in the Coast Range had been violently compressed and folded. An elevation of the land had caused the sea to withdraw from the central valley of California and had restored Lower Cali- fornia to its peninsular conditions, reducing the gulf to the narrow limits which it had had in the lower Miocene and ex- tending southern Mexico to the west and south. British Columbia and southeastern Alaska stood at higher than their present levels and the countless islands of that region were part of the mainland. Bering Strait was closed, for at least a great part of the epoch, and, as a continuous shore-line was 126 LAND MAMMALS IN THE WESTERN HEMISPHERE Fra. 52. — Map of North America during the Pliocene epoch, Bering Strait open. Ex- planation as in Fig. 48. (Modified from Schuchert.) GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 127 thus formed and a way of migration opened, the marine fauna of California and Japan became closely similar. In the interior, the Pliocene continental formations and faunas followed so gradually upon those of the Miocene, that there is great doubt as to where the line between them should be drawn. These interior formations are mostly of small extent and are very widely scattered, and much remains to be learned regarding the mammals of the epoch. In northern Kansas are the Republican River beds, which are so doubtfully Pliocene, that they may almost equally well be called upper- most Miocene. Other lower Pliocene stages, representing various divisions of time, are the Alachua of northern Florida, the Snake Creek of western Nebraska, the Thousand Creek and Virgin Valley of northwestern Nevada and the Rattlesnake of Oregon. Probably middle Pliocene is the Blanco of north- western Texas, a valley cut in the middle and lower Miocene rocks and filled in with Pliocene deposits. Possibly upper Pliocene, or, it may be, lowest Pleistocene, are the Peace Creek of southwestern Florida and the so-called ‘‘ Loup River” (not Loup Fork) of western Nebraska. The volcanic activity of the Rocky Mountain and Pacific coast regions, which was so remarkable in the Miocene, con- tinued into and perhaps through the Pliocene. The great outflow of light-coloured lava which built up the central plateau of the Yellowstone Park is referred to the Pliocene, and some of the enormous fissure-eruptions which formed the vast Columbia River fields of black basaltic lava were probably Pliocene, as some were demonstrably Miocene. Both of these epochs were remarkable for volcanic activity in the western part of the continent. The Pliocene climate, as may be inferred from the plants and marine shells, was colder than that of the Miocene, and refrigeration was progressive, as is shown by the proportion of Arctic shells in the Pliocene beds of the east coast of England, rising from 5 per cent in the oldest to more than 60 per cent 128 LAND MAMMALS IN THE WESTERN HEMISPHERE in the latest beds. In the Arctic regions the cold must have been severe, at least during the latter half of the epoch, for in the succeeding Pleistocene we find an Arctic fauna already fully adapted to the extreme severity of present day polar conditions and time was necessary for such an adaptation. In the western interior the climate was not only colder, but also drier than it had been in the Miocene, the desiccation which had begun in the latter epoch becoming progressively more and more marked. South America. -— The Greater Antilles were larger than ‘at present and Cuba was much extended, especially to the southeastward, and was probably connected with the main- land, not as one would naturally expect, with Yucatan, but with Central America; this island, it is most likely, was cut off from Hayti. The Isthmian region was considerably broader than it is now and afforded a more convenient highway of intermigration. Costa Rica was invaded by a Pliocene gulf, but it is not yet clear whether this persisted for the whole or only a part of the epoch. In the Argentine province of Entrerios is a formation, the Parand, which is most probably Pliocene, though it may be upper Miocene. This formation is largely marine and shows that the present Rio de la Plata was then a gulf from the Atlantic. A few northern hemisphere mammals in the Parand beds show that the migration had advanced far into South America. A large part of Patagonia was again submerged beneath the sea, which extended to the Andes in places, but just how general the submergence was, it is impossible to say, for the Cape Fairweather formation has been largely carried away by erosion and only fragments of it remain. Along the foothills of the Andes these beds are upturned and raised several thousand feet above the sea-level, a proof that the final upheaval of the southern mountains took place at some time later than the early Pliocene. Continental formations of Pliocene date are largely developed in Argentina ; the Araucanian stage is in two substages, one in the province GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 129 of Catamarca, where the beds are much indurated and were involved in the Andean uplift, the other, of unconsolidated materials, is at Monte Hermoso near Bahia Blanca on the Atlantic coast. The very small proportion of northern ani- mals in the Araucanian beds is surprising, but not more so than the almost complete absence of South American types in the upper Miocene and lower Pliocene of the United States. Inter- migration between the two Americas would seem to have been a much slower and more difficult process than between North America and the Old World, and the reason for the difference is probably the greater climatic barriers involved in a migration along the lines of longitude. Upper Pliocene is found in the Tarija Valley of Bolivia and probably also in Ecuador, in both of which areas the proportion of northern animals was very greatly increased. II. QuaTERNARY PERIOD The Quaternary period was a time of remarkable geo- graphical and climatic changes, which had the profoundest and most far-reaching effects, partly by migration and partly by extinction, upon the distribution of animals and’ plants, effects which are naturally more obvious than those of earlier geological events, just because they were the latest. It is cus- tomary to divide the period into two epochs, (1) the Pleis- tocene or Glacial, and (2) the Recent, which continues to the present day. 1. Pleistocene Epoch When Louis Agassiz first suggested (1840) the idea of a time, comparatively recent in the geological sense, when northern and central Europe was buried under immense sheets of slowly moving ice, like the ‘‘ice-cap”’ of modern Greenland, the conception was received with incredulity. Nearly thirty years passed before this startling theory gained the general acceptance of geologists, but now it is one of the common- places of the science, for no other hypothesis so well explains the complicated phenomena of Pleistocene geology. One great K 130 LAND MAMMALS IN THE WESTERN HEMISPHERE obstacle to the acceptance of the glacial theory was the sup- posed fact that the Pleistocene glaciation was something quite unique in the history of the earth, a violent aberration in the development of climates. Now, however, we have every reason to believe that at least three other and very ancient periods had witnessed similar climatic changes and that ‘‘ice- ages’’ were recurrent phenomena. This is not the place to discuss or even to summarize the evidence which has convinced nearly all geologists of the reality of Pleistocene glacial con- ditions on a vast scale in Asia, Europe and, above all, in North America. The reader who may wish to examine this evidence will find an admirable presentation of it in Vol. III of the “Geology” of Professors Chamberlin and Salisbury. North America. — There has long been a difference of opinion among students of the Pleistocene as to whether the glaciation was single, or several times renewed. That there were many advances and retreats of the ice, is not denied; the question is, whether there were truly interglacial stages, when the ice altogether disappeared from the continent and the climate was greatly ameliorated. The present tendency among American and European geologists is decidedly in favour of accepting several distinct glacial stages (Chamberlin and Salisbury admit six of these) separated by interglacial stages, and for this there are very strong reasons. While it is out of the question to present the evidence for this conclusion here, one or two significant facts may be noted. On the north shore of Lake Ontario, near Toronto, are certain water-made deposits, which rest upon one sheet of glacial drift and are overlaid by another. The fossils of the aqueous sediments are in two series, upper and lower, of which the older and lower contains plants and insects indicative of a climate con- siderably warmer than that of the same region to-day and corresponding to the temperature of modern Virginia. In the upper and newer beds the fossils show the return of cold conditions, much like those of southern Labrador, and this GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 131 was followed by the reéstablishment of the ice, as recorded in the upper sheet of drift. Even far to the north, on the Hudson’s Bay slope, an interglacial forest is embedded between two glacial drift-sheets. In Iowa and South Dakota numerous mammals of temperate character occur in interglacial beds. At the time of their greatest extension, the glaciers covered North America down to latitude 40° N., though the great terminal moraine, which marks the ice-front and has been traced across the continent from Nantucket to British Columbia, describes a very sinuous line. The ice was not a homogeneous sheet, moving southward as a whole, but flowed in all directions away from several, probably four, centres of accumulation and dispersal. At thesame time, the western mountain ranges had a far greater snow-supply than at present, and great glaciers flowed down all the valleys of the Rocky Mountains as far south as New Mexico and in the Sierras to southern California, while the Wasatch, Uinta and Cascade ranges and those of British Columbia and Alaska were heavily glaciated, but, strange to say, the lowlands of Alaska were free from ice. During the periods of greatest cold the rain- belt was displaced far to the south of its normal position, bringing a heavy precipitation to regions which are now ex- tremely arid. In the Great Basin were formed two very large lakes; on the east side, rising high upon the flanks of the Wasatch Mountains, was Lake Bonneville, the shrunken and pygmy remnant of which is the Salt Lake of Utah, and on the west side, in Nevada, was Lake Lahontan. Lake Bonneville, which was nearly two-thirds the size of Lake Superior, dis- charged northward into the Snake River, a tributary of the Columbia, but Lahontan had no outlet. Each of these lakes had two periods of expansion, with a time of complete desiccation between them. Over the Great Plains the principal Pleistocene formation is that known as the Sheridan, or, from the abundanee of horse-remains which are entombed in it, the Equus Beds. 132 LAND MAMMALS IN THE WESTERN HEMISPHERE These beds extend as a mantle of wind-drifted and compacted dust from South Dakota to Texas and in places contain multi- tudes of fossil bones; they correspond to one of the early interglacial stages and in South Dakota pass underneath a glacial moraine. The upheaval which came at or near the end of the Pliocene had raised the continent, or at least its northeastern portion, to a height considerably greater than it has at present, and this must have facilitated the gathering of great masses of snow; but before the end of the Pleistocene a subsidence of the same region brought about important geographical changes. The depression, which lowered the coast at the mouth of the Hudson about 70 feet below its present level, increased northward to 600 feet or more in the St. Lawrence Valley and allowed the sea to invade that valley and enter Lake Ontario. From this gulf ran two long, narrow bays, one far up the valley of the Ottawa and the other into the basin of Lake Champlain. The raised beaches, containing marine shells and the bones of whales, seals and walruses, give eloquent testimony of those vanished seas. The recovery from this depression and the rise of the continent to its present level inaugurated the Recent epoch. When the ice had finally disappeared, it left behind it great sheets of drift, which completely changed the surface of the country and revolutionized the systems of drainage by filling up the old valleys, only the largest streams being able to regain their former courses. Hundreds of buried valleys have been disclosed by the borings for oil and gas in the Middle West, and these, when mapped, show a system of drainage very different from that of modern times. Innumerable lakes, large and small, were formed in depressions and rock- basins and behind morainic dams, the contrast between the glaciated and non-glaciated regions in regard to the number of lakes in each being very striking. On the west coast events were quite different; marine Pleistocene beds in two stages are found in southern Cali- GEOGRAPHICAL DEVELOPMENT OF THE AMERICAS 133 fornia. The upheavals late in the Pleistocene, or at its close, were far greater than on the Atlantic side, 4000 feet in south- eastern Alaska, 200 feet on the coast of Oregon and rising again to 3000 feet in southern California; all the western mountain ranges and plateaus were increased in height by these move- ments. The volcanoes continued to be very active, as may be seen from the lava-sheets and streams in Alaska, all the Pacific states, Arizona and New Mexico. South America.— No such vast ice-sheets were formed in the southern hemisphere as in the northern. Patagonia was the only part of South America to be extensively covered with ice and there traces of three glaciations have been observed, of which the first was the greatest and reached to the Atlantic coast, and there were great ice-masses on the coast of southern Chili. Mountain glaciers existed throughout the length of the Andes across the Equator to 11° N. lat., the elevation increas- ing northward to the tropics. The surface of the great Argentine plain of the Pampas between 30° and 40° 8. lat. is covered with a vast mantle, largely of wind-accumulated dust, the Pam- pean, which is the sepulchre of an astonishing number of great and strange beasts. The Pampean formation corresponds in a general way to the Sheridan or Equus Beds of North America, but involves a much greater lapse of time, beginning earlier, possibly in the late Pliocene, and apparently lasting through the entire Pleistocene. While largely of zolian origin, the Pampean seems to be in part made of delta deposits laid down by rivers. One striking difference between the Pampean, on the one hand, and the Sheridan and the loess of the Mississippi Valley and of Europe, on the other, is that the former is in many places much more consolidated and stony, which gives it a false appearance of antiquity. Another and very rich source of Pleistocene mammals is found in the lime- stone caves of eastern Brazil, which have yielded an incredible quantity of such material, but not in such a remarkably per- fect state of preservation as the skeletons of the Pampean. 134 LAND MAMMALS IN THE WESTERN HEMISPHERE Very little is known of the Pleistocene in the West Indies, though probably to this date should be assigned the notable oscillations of level which are recorded in the raised sea- terraces of Cuba and other islands. The Windward groups were joined, at least in part, to the continent and large extinct rodents reached Antigua, which would not be possible under present conditions. The Isthmus of Panama was 200 feet or more higher than it is now and correspondingly wider, but was depressed to a lower than the present level, and finally raised to the height it now has. Marine beds, of presumably Pleistocene date and certainly not older, extend from the Caribbean shore to Gatun, some seven miles, and are nowhere more than a few feet above sea-level. The question of Pleistocene climates is a very vexed one and is far from having received a definitive answer. Limita- tions of space forbid a discussion of the problem here and I shall therefore merely state the conclusions which seem best supported by the evidence so far available. Such immense accumulations of ice might be due either to greatly increased snow-fall, or to a general lowering of the temperature. The balance of testimony is in favour of the latter factor and no great refrigeration is required. Professor Penck has calcu- lated that a reduction of 6° or 7° in the average yearly tem- perature would restore glacial conditions in Europe. Even the tropics were affected by the change, as is shown not only by the glaciation of the Andes, but also by Mt. Kenya, which is almost on the Equator in eastern Africa and still has glaciers. The presumably Pleistocene ice covered the whole mountain like a cap, descending 5400 feet below the present glacier limit. It was pointed out above that the interglacial stages had greatly ameliorated climatic conditions and that, in some of them at least, the climate was warmer than it is to-day in the same localities. The cause of these astonishing fluctuations and of the climatic changes in general, to which Geology bears witness, still remains an altogether insoluble mystery. CHAPTER VI THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS To every one who has paid the slightest attention to the subject, it is a familiar fact that different parts of the earth have different animals; school-children learn from their geographies that kangaroos are found in Australia, the Hippo- potamus in Africa, the Tiger in southern Asia, armadillos and llamas in South America. These examples are all taken from distant lands, yet the zodlogical difference between two given land-areas is by no means proportional to the distance between them. An Englishman landing in Japan finds him- self surrounded by animals and plants very like and often iden- tical with those which he left at home, while the narrow Strait of Lombok, east of Java, separates two profoundly different regions. In crossing Mexico from east to west, the traveller meets very different animals in closely adjacent areas; and, at first sight, the arrangement of animals appears to be so capricious as to admit of no formulation in general laws. / in pre-Darwinian times, when it was the almost universal belief that each species had been separately created and was exactly fitted to the region which it inhabits, no explanation of the geographical arrangement of animals was possible,/but the acceptance of the theory of evolution demanded that such an explanation should be found. A failure to devise any ra- tional and satisfactory account of the geography of animal life would be a fatal weakness in the evolutionary theory, hence the facts of distribution were subjected to a renewed and search- ing analysis as one of the best means of critically testing the new doctrine. Not that the subject had received no attention 135 136 LAND MAMMALS IN THE WESTERN HEMISPHERE before the publication of Darwin’s book; on the contrary, it had attracted much interest as a study of facts, and this study was one of the principal avenues by which Darwin approached his great generalization. In his autobiographical fragment he tells us: ‘‘I had been deeply impressed by discovering in the Pampean formation great fossil animals covered with armour like that on the existing armadillos; secondly, by the manner in which closely allied animals replace one another in proceeding southward over the Continent; and third, by the South American character of most of the productions of the Galapagos archipelago and more especially by the manner in which they differ slightly in each island of the group.” Obviously, before attempting to explain the facts of the geographical distribution of mammals, we must first ascertain what those facts are. The following brief sketch of the terms used in describing geographical arrangement is summarized from Mr. Wallace’s “Island Life.” - Though with fluctuating boundaries and subject to slow secular changes, a mammalian species is limited to a fairly definite area, which may be of immense or very restricted extent, and throughout which it may be found in greater or less abundance. Many species, however, are not distributed continuously over the areas which they inhabit, but occur only in suitable stations adapted to their habits and mode of life. Thus, some will be found only where there are trees, others in the neighbourhood of. water, others only on open plains, etc. A spectfic area is then the whole extent of country within which the species may be found, while the stations are the limited districts contained in the area which are exactly suited to the habits of the species in question; these stations may be hun- dreds of miles apart, as in the case of mountain-tops, or they may be close together. A marsh-living species, for example, will occur in all the marshes throughout its area, whether these be many or few, near together or widely scattered; for such a species marshes are its stations. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 137 Generic areas differ in character according as the genus is large, that is, comprising many species, or small and having but few species, or, it may be, a single one. The species, as a rule, occupy each its own area, and the areas may be entirely distinct, or they may be contiguous and more or less extensively overlapping, though it seldom happens that two or more species of the same genus inhabit exactly the same area. Often some physical feature, such as a range of high mountains, a great river, the edge of a forest, plain or desert, exactly defines the limits of species of the same genus. The Amazon, for example, acts as such a boundary to many species. It was to this change of related species from one area to another that Darwin referred in the passage quoted above, saying that he had been deeply impressed ‘“‘by the manner in which closely allied animals replace one another in proceeding southward over the Continent [7.e. South America].’’ On the other hand, the overlapping of areas may be very extensive, and one species of great range may cover the whole area of another and much more besides. A remarkable example of the widely separated areas of species belonging to the same genus is that of the tapirs. Of this genus there are two or three species in Central and South America and one inhabiting the Malay Peninsula and Borneo, almost as wide a separation as the size of the earth permits. Discontinuous distribution of this character can be explained in terms of the evolutionary theory only in one of two ways. Hither (1) the American and Asiatic species developed inde- pendently of one another from different ancestors, or (2) the regions intervening between these widely separated areas once formed a continuous land, occupied by species of the genus which have become extinct. From all that we know concern- ing the operation of the evolutionary process, the first alterna- tive may be set aside as altogether improbable, and, even had we no information concerning the history of the tapirs and their former distribution, the second explanation would be 138 LAND MAMMALS IN THE WESTERN HEMISPHERE chosen as incomparably the more likely. As a matter of fact, we have definite knowledge that tapirs once ranged all over Europe and North America and doubtless over northern Asia, as well, and, further, that North America was joined to Asia by a land occupying the place of the shallow Bering Sea, at a time when the tapirs were able to take advantage of this means of passing from one continent to the other. Such appears to be the invariable explanation of discontinuous dis- tribution, though we may not always be able to give so clear a proof of it. The genera of a family are distributed in much the same fashion as the species of a genus, but, as a rule, much more widely. While no genus of terrestrial mammals is cosmo- politan (7.e. universally distributed), at least as genera are de- fined and limited by most modern systematists, certain families are represented in every continent. If the extremely peculiar and isolated Australian continent be excepted, the number of such cosmopolitan families is considerable and wide separa- tion between the genera is frequent. Of the camel family, for instance, one genus, that of the true Camel (Camelus), is confined to the northern hemisphere and the Old World, the other (Lama), comprising the Llama, Guanaco, etc., is found only in the southern hemisphere and the New World. Less extreme instances of the discontinuous distribution of a family are common enough. The principles of distribution are the same when applied to families and orders. Most of the mammalian orders are very widely distributed and many are cosmopolitan, except for Australia, though some are confined to one or two conti- nents. The monotremes are limited to Australia and Tas- mania, the marsupials to Australia and the Americas, the edentates to the latter, the elephants and hyracoids to Africa and Asia. Carnivores and rodents, on the contrary, are found in every continent, even Australia. We have next to inquire what is the nature of the obstacles THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 139 or barriers that prevent the indefinite spread of terrestrial mammals, so that the mammalian fauna of the whole earth, and even of a single continent, is not uniform, but highly variegated. The rate of multiplication of animals is so rapid that, under normal conditions, the animal population is always pressing hard upon the means of subsistence and every species that is increasing in numbers must constantly extend its range in search of food. Every species would increase indefinitely, if there were no countervailing checks. Were all the young to survive and breed in their turn, ‘‘even large and slow-breed- ing mammals, which only have one at a birth, but continue to breed from eight to ten successive years, may increase from a single pair to 10,000,000 in forty years’ (Wallace). Evidently, a species must spread from its place of origin until stopped by insuperable obstacles, the most obvious of which are wide seas. A few land mammals are not only excellent swimmers, but will cross straits without. hesitation, as the Guanaco has been seen to swim the Straits of Magellan ; for the great majority, however, a very few miles of sea form an impassable barrier. As was shown above, a broad or deep river is sufficient to limit many species, as the Santa Cruz River in Patagonia marks the southern boundary of the armadillos. Important geographical changes, such as the joining of lands that before were separate, or the dividing of continuous lands by transgressions and incursions of the sea, must neces- sarily have a profound effect upon the distribution of land mammals. Separated land-areas, however similar may have been their faunas at the time of separation, will, through the operation of the divergent evolutionary process, grow more unlike in proportion to the length of time that the separation continues. Regions which have been severed within a short time (in the geological. sense of a short time) are zodlogically very similar or even identical, while those that have long been isolated are correspondingly peculiar. Attention has already been called, in another connection, to the contrasted cases 140 LAND MAMMALS IN THE WESTERN HEMISPHERE of such great continental islands as Great Britain, Java, Sumatra, etc., on the one hand, and Australia, on the other. The continental islands, which have but lately been detached from the neighbouring main lands, are hardly more peculiar zodlogically than equal areas of the adjoining continents, while the long-continued isolation of Australia has made it the most peculiar region of the earth. Climatic changes, which, as we saw in Chapter I, have indubitably taken place many times, have also had a great effect in shifting the distribution of mammals, which in its present form is the outcome of a very long series of geographical and climatic changes, on the one hand, and of adaptive changes in the animals themselves, on the other. Of almost equal importance as a barrier is climate and especially temperature. Not that similar climates can pro- duce similar forms in separate areas. Regions of almost exactly similar climate in Australia, Africa and South America have totally different faunas, but, within continuous’ land-areas, the most effective of barriers is temperature. “This acts dif- ferently in the case of limiting the northward spread of south- ern forms and the southward spread of northern species. Dr. Merriam’s long study of this problem has led him to the con- clusion that southern species are bounded on the north by the temperature of the breeding season, in which the total quantity of heat must reach a certain minimum, while “animals and plants are restricted in southward distribution by the mean tem- perature of a brief period covering the hottest part of the year.” On the Pacific coast there is a remarkable mingling in the same areas of species which, east of the high mountains, are dis- tributed in sharply separated zones. This is explained by the mild and equable climate of the coastal belt, where the hottest season of the year does not reach the limiting maximum for the northern species, while the total quantity of heat in the breeding season is sufficient to enable southern species to thrive and maintain themselves. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 141 Dr. Merriam thus sums up the effects of climatic factors upon distribution: ‘‘Humidity and other secondary causes determine the presence or absence of particular species in particular localities within their appropriate zones, but tem- perature pre-determines the possibilities of distribution; it fixes the limits beyond which species cannot pass.” ‘‘Con- currently with these changes in vegetation from the south northward occur equally marked differences in the mammals, birds, reptiles, and insects. Among mammals the tapirs, monkeys, armadillos, nasuas, peccaries, and opossums of Central America and Mexico are replaced to the northward by wood-rats, marmots, chipmunks, foxes, rabbits, short- tailed field-mice of several genera, shrews, wild-cats, lynxes, short-tailed porcupines, elk, moose, reindeer, sables, fishers, wolverines, lemmings, musk-oxen, and polar bears.” Dr. J. A. Allen has reached closely similar conclusions. “Of strictly climatic influences, temperature is by far the most important, although moisture plays an influential part. Where a low temperature prevails life, both animal and vegetable, is represented by comparatively few forms; under a high tem- perature it is characterized by great diversity and luxuriance. Within the Arctic Circle the species of both animals and plants are not only few, but they are widely distributed, being for the most part everywhere the same. Under the tropics they are a hundred fold more numerous and of comparatively re- stricted distribution.”” ‘‘The influence of temperature is perhaps most strikingly displayed in the distribution of life upon the slopes of a high mountain, especially if situated near the tropics. While its base may be clothed with palms and luxuriant tropical vegetation, its summit may be snow-capped and barren. ... The animal life becomes likewise corre- spondingly changed, tropical forms of mammals, birds, and insects of the lower slopes gradually giving place to such as are characteristic of arctic latitudes.” ‘The effect of humidity upon plant life is thus obvious, but it is equally potent, though 142 LAND MAMMALS IN THE WESTERN HEMISPHERE less evident, upon animal life. Many animals... are so fitted for a forest life, as regards both food and shelter, that their very existence depends upon such surroundings... . Thus moisture alone may determine the character of life over extensive regions.”’ oe While climate is thus the most important of the barriers which determine distribution in continuous land-areas, the absence of any particular species from a given region is no proof that the climate is unsuitable to that species. This is sufficiently shown by the manner in which animals introduced into a new country often run wild and multiply to an incredible extent, as the rabbits have done in Australia, the Mongoose in Jamaica, horses on our western plains, horses and cattle on the Pampas of Argentina, etc. i Topographical features, such as great mountain-ranges and plateaus, also limit many species, not only by the difficulty of crossing them, but also by the effect which they have upon temperature and moisture. For this reason long ranges of mountains and table-lands may carry a northern fauna very far to the south of its ordinary range, as do the mountain- systems of North America in a very conspicuous manner. The great Mexican plateau is zodlogically a part of North America, while the low coastal lands as far as southeastern Texas have Central American affinities. A different kind of obstacle to the spread of a species into a new area may be the pre-occupation of that area by another species. The pre-occupier may be one that plays so similar a part in the economy of nature as to leave no opportunity for the newcomer to establish itself. On the other hand, the obstructing form may be an active enemy and of a totally different character from the intruder, as in the case of the Tse-tse Fly in parts of Africa. The bite of the fly is fatal to horses and oxen, so that these mammals are unable to enter the fly-infested regions. Many times in the course of the Tertiary period various mammals reached North America THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 143 from the south or from the Old World, which were unable to gain a permanent foothold and speedily died out. At this distance of time it is seldom, if ever, possible to explain why a species which succeeded in reaching this continent could not maintain itself, though the most probable assumption is that the forms already in possession of the land were an in- superable obstacle to the intruders. The rate of dispersal of a species into new areas may be fast or slow, according as the conditions are more or less favour- able. Newly introduced insect-pests, like the Gypsy and the Brown-tailed Moths in New England, often spread with por- tentous rapidity ; and introduced mammals have frequently taken possession of vast areas in a surprisingly short time. One of the most remarkable of these cases is cited by Darwin. “In the time of Sarmiento (1580) these Indians had bows and arrows, now long since disused ; they then also possessed some horses. This is a very curious fact, showing the extraor- dinarily rapid multiplication of horses in South America. The horse was first landed at Buenos Ayres in 1537 and the colony being then for a time deserted, the horse ran wild; in 1580, only forty-three years afterwards, we hear of them at the Strait of Magellan !’’ (‘‘ Voyage of a Naturalist,” pp. 232- 233.) In this example, something must be allowed for human agency, but even so, it is very surprising. In the case of lands newly raised above the sea and con- necting formerly separated areas, itisnecessary that they should first be taken possession of by vegetation, before they can become passable by animals, for the migration of mammals from continent to continent is an entirely distinct phenomenon from the annual migration of birds. The latter, though a fact familiar to every one, is an unexplained mystery, and it is some- what unfortunate that the same term should be used for the completely different process of the spread of mammals into newly opened land. This spread is purely unconscious and is due to the pressure of increasing numbers upon the means of 144 LAND MAMMALS IN THE WESTERN HEMISPHERE subsistence, each new generation ranging farther and farther from the original home of the species and continuing so to extend until some insuperable obstacle is encountered. When a sea-barrier is removed by upheaval and the newly formed land rendered habitable for mammals through the invasion of plants, the interrupted process is resumed and an inter- change of species between the areas thus connected is brought about. The interchange is, however, always an incomplete one, certain forms not being able so to extend their range, because of climatic differences, pre-occupation or some such barrier. It is customary to give a graphic expression to the facts of animal distribution by dividing the land surface of the earth into districts which are characterized by their faunas. It is not possible to construct a geographical scheme which will be equally satisfactory for all classes of animals, because the geological date of most rapid development and diffusion was so different in the various classes. The geographical and climatic conditions which favoured a particular geographical arrangement of one class had been so completely altered that the class coming in later could not attain a similar distribution. For this reason, land mammals are chosen as affording the best criteria; their adaptability is such that they are found all over the earth, their dispersal is primarily dependent upon the arrangement and connections of the continental land-masses, modified by the topographical and climatic conditions, and they, with the birds, are the latest of the vertebrate classes to assume a dominating importance. Their history is the most fully known and falls within the best understood portion of the earth’s history, making it possible to follow their migrations with a precision which is seldom feasible for the other classes of animals, and thus to correlate the successive physical and organic changes. A particularly great advantage which mam- mals possess for this purpose is that the mutual relationships of the various kinds are better understood than in the case of THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 145 most other groups of animals. It is true that we shall find a great many unsolved problems, upon which the most divergent opinions are held, but the main outlines of the scheme are quite generally agreed upon. Many plans for the zoélogical division of the continental areas have been proposed by various writers on the subject, some differing very radically from others. It would be useless and tedious to review even the more important of the many proposals and suggestions which have been made in the last half-century ; and we may, with advantage, adopt an eclectic scheme which has been slowly reached by successive approx- . imations to a satisfactory arrangement. Just as in political geography it is found necessary to rec- ognize divisions of different rank and scope, like nation, state, county, township, the facts of zodlogical geography require divisions of different orders of importance. Thus, in descend- ing order, the terms realm, region, subregion, province, etc. are commonly employed, but unfortunately they are often used loosely and even interchangeably ; yet it is desirable to attach a more or less precise significance to each and more terms are needed for an accurate expression of the many complex facts. The extreme zoological peculiarity of Australia is recognized by making that continent and its adjoining islands one of the great primary divisions, of which the other includes all the rest of the world; the former is characterized by its almost exclusively marsupial fauna, while the other continents are inhabited by the Monodelphia or placental mammals. Aside from Australia, by far the most isolated and peculiar region of the earth is South America, and this fact is expressed by constituting it into a realm, or division of the second order, and to this realm is given the name Neogea. The remaining con- tinents, North America, Europe, Asia and Africa, make up the other realm, Arctogea, in which there is an unmistakable -general likeness among the mammals. The three continents L 146 LAND MAMMALS IN THE WESTERN HEMISPHERE of the Old World form a vast, connected land-mass, and the final separation of North America from this great complex is an event of geologically recent date. For reasons that will be made clear in the course of the history, the junction of the two Americas has had comparatively little effect upon the zoélogy of the northern continent, except in its tropical portion. It is obvious from a glance at the map, that the great zodlogical divisions are of very unequal size, but the arrangement is made on the basis of degrees of difference in the mammalian faunas. These degrees of difference are, in turn, an expression of length of separation or of the difficulty of communication between connected lands. The following table gives the major divisions of the earth apart from Australia: I. Neocaic Reatm. Neotropical Region.—South and Central America, lowlands of Mexico, the West Indies. { 1. Malagasy Region. — Madagascar. 2. Ethiopian Region. — Africa south of the Sahara Desert. ; 3. Oriental Region. — Southern peninsulas of Asia, II. Arcrocaic REALM. Malay Archipelago. | 4. Holarctic Region. —N. Africa, Europe, Asia, (except southern part), boreal N. America. 5. Sonoran Region. — Remainder of N. America | (except lowlands of Mexico). North America, as is expressed by this scheme, is zodlog- ically composite; the northern half, including nearly all of Canada, belongs to the vast Holarctic Region, which also comprises Europe, Africa north of the Sahara and Asia north of the Himalaya Mountains. The remainder of the continent, exclusive of the Mexican coastal lowlands, is set off as the Sonoran Region. Inasmuch as we have here to do with broadly continuous land-areas, not demarcated by great physi- cal features, and as the genera and species of mammals differ greatly in regard to their ability to withstand a wide range of climatic variations, it is not to be expected that the boun- THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 147 daries between the regions which make up North America should be very sharply drawn. It is not surprising, therefore, to find a transition zone, extending all across the continent, in which the Holarctic and Sonoran faunas mingle, or that Central America should, in considerable measure, be transi- tional to South America, though zoélogically a part of the latter. we | \w =a a ee ( i ye ( . Arctic zone Boreal zone or Canadian subregion Transition zone A Sonoran region YJ), *2+rvical region Fic. 53. — Zodlogical Divisions of North America. (After Merriam.) 148 LAND MAMMALS IN THE WESTERN HEMISPHERE Dr. Merriam’s arrangement, which deals only with North America without reference to the Old World, divides the land into a series of transcontinental zones, which he calls the Arctic, Boreal, Upper and Lower Sonoran and Tropical. These zones have very irregular and sinuous boundaries, which follow lines of equal temperature (isothermal lines) during the breeding season, May, June and July, the tortuous boundaries being conditioned by topographical features, which deflect the isothermal lines. Fig. 54. — Polar Bear (Thalarctus maritimus). — By permission of the N.Y. Zodlog. Soc. The Arctic zone is part of a circumpolar area, which is very much the same in North America, Asia and Europe; and in any of these continents the fauna differs much more from that of the contiguous zone to the south than from the Arctic fauna of another continent. There are some local differences, but the characteristic mammals of this Arctic zone are the Polar Bear, Arctic Fox, Musk Ox, Barren-ground Caribou, Lemming, THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 149 Fic. 55. — Musk Ox (Ovibes ward) female; the males have much larger horns. — By permission of the N.Y. Zodlog. Soc. Fic. 56.— Arctic Fox (Vulpes lagopus) in winter dress. — By permission of the N.Y. Zodlog. Soc. 150 LAND MAMMALS IN THE WESTERN HEMISPHERE Arctic Hare,anda marmot. Most, if not all, of these forms are of Old World origin. The American portion of the great Holarctic region is called by Mr. Lydekker, who uses Wallace’s term, the ‘‘Cana- dian subregion,” and by Dr. Merriam the ‘‘ Boreal region.”’ Not that there is any difference of principle involved in this varying nomenclature, for Dr. Merriam says: ‘‘It so happens that the Boreal element in America resembles that of Eurasia so closely that in the judgment of many eminent authorities the two constitute a single primary region — a view in which I heartily concur.”’ The Canadian or Boreal subregion of the Holarctic is the great belt of coniferous forest, which extends obliquely across North America from Alaska to New England; its frontier with the Arctic zone is the northern limit of trees and Fia. 57.— Arctic Fox in summer dress. — By permission of the N.Y. Zodlog. Soc. it is divided from the Transition zone approximately by the line of latitude 45° N., though with a sinuous course, and it is carried far to the south by the wooded heights of.the Appa- lachian, Rocky and Sierra Nevada Mountains, and along the Pacific coast, the mixed character of which has already been explained; it extends almost to San Francisco. The sub- THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 151 region is further divisible into northern and southern belts, called the Hudsonian and Canadian faunas, the limit between them approximately following the isothermal line of 57° F. The mammals of this subregion are largely of Old World origin, many of them coming in with the great immigrations of the Pliocene and Pleistocene epochs; but there are also native American elements and even one genus of South American origin, the Short-tailed or Canada Porcupine (Erethizon). In considering the mammals of this subregion, it should be remembered that they are not uniformly distributed through- out even one subdivision, but in a scattering way and in ac- cordance with their habits and stations, and also in accordance with a gradual change to the south, following the changing temperature. The Muskrat will not be found far from water or the Por- cupine from woods. Espe- cially characteristic of the Canadian subregion are the Old World types of deer, none of which range farther south than the Transition zone. The Wapiti, errone- ously called the Elk (Cervus canadensis), is very closely allied to the European Stag (C. elaphus) and still more —er” closely to the Stag of the bh ‘ p Fie. 58. — Canada Porcupine (Erethizon dorsa- Thian Shan in Central Asia tus). — By permission of the N.Y. Zodlog. (C. eustephanus). So great Ron. is the resemblance, that some naturalists would refer all three forms to a single species. The Moose (Alce americanus), which should be called the Elk, is so near to the Scandinavian Elk (A. machlis) that it is hardly distinguishable as a separate aa 152 LAND MAMMALS IN THE WESTERN HEMISPHERE species, and the Woodland Caribou (Rangifer caribou) is the American representative of the Lapland Reindeer (R. tarandus). The so-called Rocky Mountain Goat (Oreamnos montanus), a peculiar and aberrant form of the Chamois subfamily of the Ante- lopes, is confined to the subregion. The Moun- tain Sheep (Ovis mon- tana, O. dalli) are rep- resented by three or four species, one of Fig. 59. — Woodchuck or Marmot (Marmota monaz). Which extends into the —By permission of the N.Y. Zodlog. Soc. Sonoran region, as does also the Bison, wrongly called Buffalo (Bison bison), which is nearly allied to the European B. bonasus. In Cesar’s time the European Bison (German, Wisent) ranged through Ger- many and is described in his account of the Hercynian Forest ; but the advance of civilization has almost exterminated it, only a few small herds being maintained by the most rigid protection in Russia and in the Carpathian Mountains. Of the Car- nivora, the weasels, mar- tens, Fisher, Mink and Ermine are Boreal, as are the Wolverene (Gulo) and the Grey Wolf (Ca- nis), the three last- | .+ named extending also into the Arctic zone. Es- Fie. 60,— Mink (Lutreola vison). — By permission sentially Boreal, though GE ERE ELT AOL, OK reaching and entering the Sonoran, are the bears (Ursus), the red foxes (Vulpes), the otters (Lutra) and the Old World shrews (Sorex), while the Star-nose Mole (Condylura) and THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 153 the mole-shrews (Urotrichus) do not extend south of the Transition zone. Probable intruders from the south into the Boreal subregion are the pumas, or ‘“ mountain lions,” which just enter the subregion, the Canada Lynx (Lynx rufus) and one species of skunks (Mephitis), the Raccoon (Procyon lotor), Badger (Taxidea americana) and the Ameri- can deer (Odocoileus). A large number of rodents are char- acteristically Boreal: marmots, or woodchucks (Marmota), the Sewellel (A plodontia rufa), lemmings (Myodes), Jumping Mouse (Zapus), the Canada Porcupine (Erethizon dorsatus) and the pikas, “‘tailless or whistling hares’? (Ochotona). Boreal ro- dents that enter the Sonoran are the chipmunks (Tamias), beavers (Castor), meadow-mice (Microtus), the Muskrat (Fiber zibethicus). The white-footed mice (Sitomys) and the wood- rats (Neotoma) are southern rodents that reach or enter the Boreal. Between the Boreal subregion and the Sonoran region is the Transition zone, which follows all the complex windings of the boundary lines. It covers most of New England, New York, Pennsylvania and southern Ontario; passing through southern Michigan and Wisconsin, it bends northward over Minnesota and covers most of North Dakota, Manitoba and the plains of the Saskatchewan, then turns abruptly south- ward and includes eastern Montana and parts of South Dakota and Nebraska. Crossing Wyoming, it follows around the northern edge of the Great Basin to the plains of the Columbia. The three great mountain-systems carry the zone far to the south and arms of it extend along the Appalachians to northern Georgia, along the Rockies to New Mexico, and it follows the Sierras to southern California. ‘‘The Transition zone, as its name indicates, is a zone of overlapping Boreal and Sono- ran types. Many Boreal genera and species here reach the extreme southern limits of their distribution and many Sonoran genera and species their northern limits. But a single mam- malian genus (Synaptomys) [one of the field mice] is restricted % 154 LAND MAMMALS IN THE WESTERN HEMISPHERE Fic, 61.— Upper figure, European Bison (Bison bonasus). Lower figure, American Bison (B. bison). — By permission of the N.Y. Zodlog. Soc. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 155 Fic. 63.— Wapiti or ‘‘ Elk”’ (Cervus canadensis).— By permission of the N.Y. Zodlog. Soc. 156 LAND MAMMALS IN THE WESTERN HEMISPHERE Fic. 64.— Alaska Brown Bear (Ursus middendorfi).— By permission of the N.Y. Zodlog. Soc. Vic. 65.— Moose (Alce americanus). Young male with undeveloped antlers. — By permission of the N.Y. Zodiog. Soc. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 157 Fic. 67.— Woodland Caribou (Rangifer caribou). — By permission of the N.Y. Zodlog. Soc. 158 LAND MAMMALS IN THE WESTERN HEMISPHERE Fic. 69.— Rocky Mountain ‘‘ Goat’ (Oreamnos montanus). — By permission of the N.Y. ZoGlog. Soc. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 159 Fic. 70.— Ermine (Mustela ermine1). — By permiss'on of the N.Y. Zodlog. Soc. kG. 71.— Timber or Grey Wolf (Canis nubilis). — By permission of the N.Y. Zodlog. Soc. 160 LAND MAMMALS IN THE WESTERN HEMISPHERE * Senet enemay ze Fic. 72.— Boreal Mammals. A. Black-footed Ferret (Mustela nigripes). B. Otter (Lutra canadensis). C. Jumping Mouse (Zapus hudsonius).— A and B by permis- sion of the N.Y. Zoédlog. Soc. C, by permission of W.S. Berridge, London. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 161 to the Transition zone. . .. A number of species, however, seem to be nearly or quite confined to this zone’’ (Merriam). The most characteristic portion of North America, zoélog- ically speaking, is the Sonoran region of Dr. Merriam, the Warm Temperate of Dr. Allen. It crosses the continent from ocean to ocean, its northern boundary following for most of the way the 43d parallel of latitude, but over the Great Fic. 73. — Opossum (Didelphis marsupialis). — By permission of the N.Y. ZoGlog. Soc. Plains and Great Basin, on each side of the Rocky Mountains and the high plateaus, it extends to lat. 48°. On the south, it takes in the greater part of Mexico, covering all of the table- land of that country, the lowlands of which belong to the South American or Neotropical region. The Sonoran is invaded from the north by the long branches from the Boreal and Transition zones, which follow the three great mountain-systems in the manner already explained, and the Mexican plateau permits the similar invasion of Neotropical territory by the Sonoran fauna. Characteristic Sonoran genera, none of which extend into the Boreal, are the opossums (Didelphis), in the southern part a peccary (Tagassu) or ‘‘ Wild Texas Pig,” representative of a family of swine quite different from the true pigs of the Old M 162 LAND MAMMALS IN THE WESTERN HEMISPHERE World, and an armadillo (Tatu). A very isolated form is the Prong-horned Antelope (Antilocapra americana); there are several species of the typically American deer (Odocoileus) which differ in important respects from those of the eastern Fic. 74. — Prong-horned Antelope (Antilocapra americana). — By permission of the N.Y. ZoGlog. Soc. hemisphere, and the Bison was very abundant until exterminated by Man. Bison, antelope and deer also reach or extend into the Boreal zone, but the former, or Wood Bison, is probably a different species from the plains animal. The grey foxes (Urocyon), Coyote (Canis latrans), large Timber Wolf (Canis occidentalis), the Caxomistle (Bassaris- cus), the Coati (Nasua), Raccoon (Procyon), Badger (Tazi- THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 163 dea), three genera of skunks, pumas, several species of lynx and some bears (Ursus) represent the Carnivora, though one species each of raccoon, skunk, badger, puma and lynx range Fic. 75. — Kangaroo-Rat (Dipodomys philippii).— By permission of the N.Y. Zoélog. Soc. into the Boreal. The American types of shrews (Blarina) and moles (Scalops and Scapanus) are characteristic of the Sonoran, though partially shared with the Boreal. A great Fic. 76. — Thirteen-lined Sperrnophile (Spermophilus tredecimlineatus). — By permission of the N.Y. Zodlog. Soc. many peculiar rodents inhabit the Sonoran; cotton-rats (Sig- modon), pocket-gophers (Geomys, etc.), several genera of the beautiful little kangaroo-rats (Dipodomys, etc.); while the 164 LAND MAMMALS IN THE WESTERN HEMISPHERE prairie-dogs (Cynomys), the white-footed mice (Sitomys), wood-rats (Neotoma) and one genus of pocket-gophers (Thom- omys) are chiefly Sonoran, but have Boreal representatives. The flying squirrels (Sciuropterus), true squirrels (Sciurus), ground-squirrels (Sper- mophilus), rabbits (Le- pus), wolves (Canis) and otters (Lutra) have a very wide range through both the Bo- real and Sonoran, but have many more spe- cies in the latter region. Fic. 77. — Grey Squirrel (Sciurus carolinensis). The Sonoran region — By permission of the N.Y. Zodlog. Soc. may be divided into the upper and lower Sonoran zones, which are demarcated by temperature and are of transcontinental extent. Each of these zones may, in turn, be subdivided into arid and humid provinces, but our purpose does not necessitate entering into such refinements. The Neotropical, which is the only region of the Neogeic realm, comprises the West Indian islands, all of Central and South America and the lowlands of Mexico, extending a short distance into southeastern Texas. Of its four sub- regions, the most typical is (1) the Brazilian, which includes not only Brazil, but all of South America east of the Andes and as far south as Paraguay, and is a vast area of tropical forests. (2) The Chilian subregion takes in the west coast, the high Andes and the southern end of the continent, south of the Brazilian subregion ; it is a country chiefly of open plains and high mountains, and a few deserts, of which South America has less than any other continent, except Europe, which has none. (3) The Central American subregion reaches from the THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 165 Fig. 78. — Grey Fox (Urocyon virginianus).— By permission of the N.Y. Zodlog. Soe. Fic. 79. — Prairie Wolf or Coyote (Canis latrans). — By permission of the N.Y. Zodlog. Soc. 166 LAND MAMMALS IN THE WESTERN HEMISPHERE Fic. 81.— Virginia Deer (Odocoileus virginianus). — By permission of the N.Y. Zodlog. Soc. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 167 Fia. 82. —Skunk (Mephitis mephitis). —By permission of the N.Y. Zodlog. Soc. Fic. 83. — Mule Deer (Odocoileus hemionus). — By permission of the N.Y. Zodlog. Soc. 168 LAND MAMMALS IN THE WESTERN HEMISPHERE Fic. 84.— Badger (Tazxidea americana).— By permission of the N.Y. Zodlog. Soc. Fic. 85. — Puma or Mountain Lion (Felis concolor). — By permission of the N.Y. Zodlog. Soc. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 169 Fig. 86.— Lynx (Lynx rufus).— By permission of the N.Y. Zodlog. Soc. Fic. 87. — Prairie Dog (Cynomys ludovicianus).— By permission of the N.Y. Zodlog, Soc. 170 LAND MAMMALS IN THE WESTERN HEMISPHERE i Hygll ata Hi i Hi itu a iyi i Ys il tl ! Nh il wl iT nT TET Tee o qu i ‘ani i i Il in l wy ql H r | Wage ' ty { hy : i i i Fic. 88.— Map of the Neotropical region. (After Wallace.) Mexico inaccurate ; of. Fig. 53, p. 147. Isthmus of Panama to Mexico, the lowlands of which are in- cluded and even a small portion of southeastern Texas. (4) The West Indian subregion includes all the islands of that archipelago, except Trinidad, which is a fragment of the con- THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 171 tinent, detached at a comparatively recent date; the southern extremity of Florida also belongs to this subregion. The two subregions into which continental South America is divided are not altogether satisfactory and will doubtless require change when the distribution of South American mammals has been more accurately determined. Fic. 89.— Fox-like Wolf (Cerdocyon gracilis). — By permission of W.S. Berridge, London. ‘Richness combined with isolation is the predominant feature of Neotropical Zodlogy, and no other region can approach it in the number of its peculiar family and generic types’? (Wallace). Just as North America has received many immigrants from the Old World, so it has sent many mi- grants into South America, materially changing the character of the Neotropical mammalian fauna, but these intruders may be readily identified and almost seem to be out of place in their new surroundings. Not all of these northern migrants were 172 LAND MAMMALS IN THE WESTERN HEMISPHERE able to maintain their footing in the southern continent and several became extinct during and at the close of the Pleistocene epoch, as was even more markedly the case with the southern forms which invaded the northern continent. . Fic. 90.—Spectacled Bear (Tremarctos ornatus).— By permission of the N.Y. Zodlog. Soc. There are two families of monkeys in the forested areas of South America, both very different from those of the Old World. One of these families, the marmosets (Hapalide), dif- fers from all other monkeys in several particulars, most obvious of which are the long claws on the feet and the non-opposable thumb. The second family (Cebide#) comprises forms which are superficially much more like those of the eastern hemi- sphere, but many of them have prehensile tails, which are used as efficient grasping organs. Insectivora are entirely absent from the South American THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 173 continent, but some shrews (Blarina) have entered Central America from the north and a very curious genus is represented by one species in Cuba (Solenodon cubanus) and another in Hayti (S. paradorus). These remarkable animals are, strange eee ’ aN Nf ie ae ie =o a eee aR ieee rey ; c en irae oe a Fic. 91.— Solenodon cubanus.— By permission of the N.Y, Zodlog. Soc. to relate, most nearly allied to the tenrecs (Centetes) of Mada- gascar and by some authorities are placed in the same family. The Carnivora are quite numerous and varied and rather peculiar, but they all belong to northern families and are the more or less modified descendants of northern immigrants. The dogs (Canidz) belong to genera not represented else- where and form a considerable assemblage of interesting types. There are no true wolves or foxes, but several species of fox-like 174 LAND MAMMALS IN THE WESTERN HEMISPHERE Fic. 92.— Argentine Skunk (Conepatus gibsont).— By permission of W.S. Berridge, London. wolves (Cerdocyon), with bushy tails, are common, especially in the plains regions. The Bush-Dog (Icticyon venaticus), a small, short-legged animal, is very peculiar. The musteline or weasel family (Mustelide) is rather scantily represented. There are no badgers and but few skunks (Spilogale and Conepatus) ; Fic, 93.— Little Skunk (Spilogale putorius).— By permission of W.S. Berridge, London. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 175 a we 2 of. Fic. 94. — Tayra (Tayra tayra). — By permission of W. 8. Berridge, London. weasels are absent, but their place is taken by the Grison (Galera vittata) and Tayra (Tayra tayra) and in the far south Lyncodon patagonicus. These animals are peculiar in having a lighter colouration on the back than on the belly. There are two or three species of otter (Lutra). The raccoons (Procyon) have a very wide range in South America, as in the Fic. 95.— Kinkajou (Potos caudivolvulus), Central America. — By permission of W.S. Berridge, London. 176 LAND MAMMALS IN THE WESTERN HEMISPHERE northern continent, and the curious, long-snouted coatis (Nasua), which just enter the Sonoran region, are typically Neotropical. The Spectacled Bear (Tremarctos ornatus) is the only member of the family that occurs in South America and is confined to the highlands of Peru and Chili. The cat family is quite numerously represented; the Jaguar (Felis onca), which ranges from Texas to Patagonia, is a large spotted cat, rivalling Fic. 96. — Ocelot (Felis pardalis). —By permission of the N.Y. Zodlog. Soc. the Leopard in size and ferocity; the Ocelot (F. pardalis, Arkansas to Paraguay) is smaller and streaked and blotched rather than spotted. The pumas differ little from those of North America, and there are many small cats, spotted, clouded and of solid colour, but no lynxes, which are essentially northern types. Hoofed animals are not numerously represented in South America. The only existing Perissodactyla of the western hemisphere are the tapirs (Tapirus) of Central and tropical South America, a very remarkable contrast to the ancient faunas, especially of the northern continent, as will be shown in the sequel. The Artiodactyla are more varied, though very scanty in comparison with those of the Old World ; even North America, which has but a poor representation of these animals, THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 177 Fic, 97.— Jaguar (Felis onca). — By permission of the N.Y. Zodlog. Soc. Fig. 98.— Collared Peccary (Tagassu tajacu).— By permission of the N.Y. Zodlog. Soc. 178 LAND MAMMALS IN THE WESTERN HEMISPHERE is much richer than the southern continent, where, indeed, all the hoofed animals are the descendants of comparatively recent immigrants from the north and none are truly autoch- thonous. Members of three different artiodactyl suborders occur in the Neotropical region; the peccaries (Tagassu) extend through Central and South America to Paraguay, Fic. 99. — Vicufia (Lama vicunia).— By permission of the N.Y. Zodlog. Soc. though also entering the Sonoran region in Texas. Most interesting are the members of the camel family, which are very distinct from the true Camel of Asia. Tierra del Fuego and the Patagonian plains support great herds of the Guanaco (Lama huanacus), which extends along the Andes to Ecuador and Peru, where it is associated with the Vicufia (L. vicunia), a smaller and more slenderly built species. The Vicufia does not range south of Bolivia. Just as the mountain systems of North America carry the Boreal and Transition faunas through . nearly the whole breadth of the Sonoran region, so the high THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 179 Andes afford a pathway by which the mammals of the south temperate zone extend their range to the equator. The suborder Pecora of the Artiodactyla is represented in the Neotropical region only by the deer family (Cervide), of which there are several genera (or subgenera), all of them North American as distinguished from the Old World type, Fic. 100. — Florida Deer (Odocoileus virginianus osceola). -— By permission of the N.Y. Zodlog. Soc. but some are so peculiar that they must have had a relatively long South American ancestry. The Virginia Deer (Odo- coileus virginianus) of the northern United States is a com- paratively large animal, becoming much smaller in Florida and the Southwest. The type extends through Mexico and Central America to Guiana and Peru, the Neotropical forms being so small and having such weak antlers that they are referred to separate species. Another type is the Marsh Deer 180 LAND MAMMALS IN THE WESTERN HEMISPHERE (Blastoceros paludosus) of eastern South America, which has short, stout antlers, each beam with two double bifurcations ; there are other species of the same genus, such as the Pampas Deer of Argentina (B. bezoarticus). In the Andes of Peru and Chili and the forests of western Patagonia are two species of a genus which bears the preposterous name of Hippocamelus Fic. 101. — Marsh Deer (Blastoceros paludosus), female. — By permission of the N.Y. Zodlog. Soc. and in which the antlers are simply forked. The vernacular name of these animals is ‘‘Huemul.’”’ Peculiarly Neotropical are the little brockets, which hardly exceed a height of two feet at the shoulder, with simple spike-like antlers not more than three inches long; the genus, Mazama, has several species, one of which occurs as far north as the state of Puebla in Mexico. “The smallest of all deer is the Chilian pudu (Pudua pudu), THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 181 a creature not much larger than a hare, with almost rudimen- tary antlers’? (Lydekker). Old World types of deer, such as the Wapiti, Moose and Caribou, of the Boreal and Transi- tion zones of North America, are entirely absent from the Neotropical region. South America has an astonishingly rich and varied assem- blage of rodents, both indigenous and immigrant, but the Fic. 102. — Wood Brocket (Mazama nemorivagus). — By permission of W.S. Berridge, London. former are much the more important, varied and abundant. Of the four divisions of the order, all of which are represented, three are immigrants from the north and the fourth is autoch- thonous, but this far outnumbers the other three combined. The hares and rabbits have but very few species, one of which occurs in Brazil and is separated by a very wide interval from the one in Costa Rica, while the pikas are absent. Of the squir- rel division, only the true squirrels are found, and of these there are many species, the ground-squirrels, marmots, prairie-dogs 182 LAND MAMMALS IN THE WESTERN HEMISPHERE and beavers all being lacking. In the same way the rat and mouse division is represented by a single family. The vesper or white-footed mice (Sitomys) have invaded the southern continent and a number of peculiar genera have arisen there, but all of northern ancestry, such as the groove-toothed mice (Rheithrodon) and the fish-eating rats (Ichthyomys). The Fic. 103. — Brazilian Tree Porcupine (Coendou prehensilis).— By permission of the N.Y. Zodlog. Soc. voles, or meadow-mice, the muskrats, jumping mice, kan- garoo-rats and pocket-gophers of the northern continent are all absent. While the immigrant suborders have thus but one family each in South America, the case is very different with the fourth or porcupine group, of which that continent is to-day, as it has been for ages past, the headquarters. No less than six families and twenty-nine genera are known, all of the genera and four of the families being restricted to the Neotropical region. Contrast this assemblage with the ex- treme scantiness of this group in North America, where but a@ single genus, the Short-tailed or Canada Porcupine (Ere- Fic. 104. — Neotropical rodents. A. Vizcacha (Viscaccia). B. Paca (Agouti paca). C. Rock Cavy (Cavia rupestris). D.Water-Hog, or Carpincho (Hydrocherus). D, by permission of the N.Y. Zodlog. Soc. A, B, C, by permission of W. 8. Berridge, London. (183) 184 LAND MAMMALS IN THE WESTERN HEMISPHERE thizon) represents it, and that is a late immigrant from the south. It would lead us too far to attempt a description of this horde of curious and interesting rodents, so only a few of the more striking and characteristic forms can be mentioned. There are two genera of porcupines (Coendow and Chetomys), both arboreal, which belong in the same family as the North American Erethizon, but are distinguished by their long, prehensile tails, which they use, as monkeys and opossums Fie. 105. — Chinchilla (Chinchilla laniger). — By permission of W. 8S. Berridge, London. do, for grasping and climbing. The very large family of the Octodontide has 17 Neotropical genera and four others are found in Africa. The Degu (Octodon) of Chili, Bolivia and Peru has the appearance of a large rat with tufted tail; the tuco-tucos (Ctenomys) are extremely abundant burrowers in Patagonia, where they honeycomb the ground over wide areas. The spiny rats (Hchimys and Loncheres) are so called from their appearance, not because they are related to the true rats; they have numerous horny spikes through the fur of the back. The Coypu (Myocastor) is a large, aquatic animal, remotely like the northern Muskrat, and the Hutias (Capromys and Pr THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 185 Plagiodontia) are arboreal and found only in Cuba, Hayti and Jamaica. The chinchillas (Chinchilla and Lagidiwm) of the Andes and the Vizcacha (Viscaccia) of the Argentine plains have somewhat the appearance of hares, but with long and bushy tails. The cavies, to which the familiar, misnamed Guinea-Pig (Cavia porcellus) belongs, are a very characteristic family; besides the true cavies, it includes the Patagonian Mara (Dolichotis), a large, long-legged, long-eared, short- tailed creature, and the Water-Hog, or Carpincho (Hydro- cherus), an aquatic animal, as its name implies, and much the Fic. 106. — Hairy-rumped Agouti (Dasyprocta prymnolopha). — By permission of W.S. Berridge, London. largest of existing rodents; it occurs in the warmer regions, south to Argentina. The heavy Paca (Agouwti) and the slender-limbed Agouti (Dasyprocta) make up another family. Altogether, this assemblage of the porcupine-like suborder of rodents is a very remarkable one and in no other region of the earth is anything like it to be found. With the exception of one genus of armadillos, which has invaded Texas, the entire order of the Edentata is at present confined to the Neotropical region, the so-called edentates of the Old World now being removed to other orders. The 186 LAND MAMMALS IN THE WESTERN HEMISPHERE Edentata, which were once far more varied and abundant than they now are, comprise three groups of animals so bizarre and strange that they seem more like fabulous creatures than actual, living mammals. One group, or suborder, is that of the sloths (Tardigrada), arboreal, shaggy animals, with short, Tic. 107. — Three-toed Sloth (Bradypus tridactylus). — By permission of the N.Y. Zodlog. Soc. almost monkey-like head and no tail; their very long legs and hook-like feet make them nearly helpless on the ground, but are very useful for hanging from the branches of the trees, in which the creatures live. Indeed, the sloths are the only mammals which habitually hang in a suspended position. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 187 Two genera of sloths inhabit the tropical forests, between which the most obvious difference is that in one (Bradypus) the fore- foot has three toes, and in the other (Cholepus) two. The suborder of the anteaters (Vermilingua) is more varied, and is the only one of the order to which the term ‘‘edentate”’ Fic. 108. — Two-toed Sloth (Cholepus didactylus). — By permission of W.S. Berridge, London. applies strictly, for they alone in the order are altogether toothless. The great Ant-Bear (Myrmecophaga jubata), which may reach a total length of seven feet, has an extravagantly long, slender and nearly cylindrical head, long, shaggy, black and white hair and an immense, bushy tail; the forefeet are armed with huge, sharp-pointed claws, which are used for tearing open ant-hills, and when occasion arises, as formidable weapons of defence, for the Ant-Bear can successfully repulse even the Jaguar. In walking, the claws are curved inward and the preposterous beast rests his weight upon the outside edges of the forefeet, while the hind feet apply the sole to the ground, as does a bear or raccoon. The Collared Anteater (Tamandua) is much smaller and mainly arboreal in habits. It has a short-haired, black body, with a white stripe down the 188 LAND MAMMALS IN THE WESTERN HEMISPHERE Fig. 109. — Ant-Bear (Myrmecophaga jubata). — By permission of the N.Y. Zodlog. Soc. back, white neck and limbs, a colour-pattern which gives to the animal the appearance of wearing a close-fitting black jacket; the long tail, which has some cross bars, is short- haired, very different from the extremely bushy tail of the Ant- Bear. The little Two-toed Anteater (Cyclopes didactylus), Fic. 110.— Collared Anteater (Tamandua tetradactyla). — By permission of the N.Y. Zoélog. Soc. THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 189 hardly larger than a rat, is exclusively arboreal and has a pre- hensile tail, like so many other South American mammals. Sloths and anteaters are forest animals and are not found west of the Andes or south of Paraguay. The third existing suborder of edentates is that of the arma- dillos (Dasypoda), which have a very complete armour of bony scutes, ossifications in the skin, covered with scales of horn. They are all more or less burrowers in habit and omnivorous Fig. 111. —Six-banded Armadillo (Dasypus sexcinctus). — By permission of the N.Y. Zodlog. Soc. in diet, eating roots, insects, worms, etc.; the extraordinary rapidity with which they burrow into the ground is almost their only way of escape from pursuit, but in one genus, T'oly- peutes, the animal can roll itself into a ball, completely pro- tected by mail all around. The armadillos are much more varied than the anteaters or sloths and have a wider geo- graphical range, extending from Texas to Patagonia. The head, which is long-snouted, is protected by a shield made up of numerous horn-covered platesof bone, and the tail is encased in a tubular sheath of more or less regular rings, each ring of bony plates and horny scales. The body-shield, or cara- pace, which covers the back and sides, consists of an anterior and posterior buckler, in which the plates are immovably 190 LAND MAMMALS IN THE WESTERN HEMISPHERE attached to one another by their edges, and between the two is a series of movable, overlapping bands, the number of which varies in the different genera. In the little Pichiciago (Chlamy- dophorus truncatus) the head and back are covered with four- sided plates of horn, the bony scutes being small and thin and much reduced. The carapace has no bucklers, but about 20 transverse rows of plates, and is attached along only the middle line of the back and beneath it the body is covered with silky, Fig. 112.— Nine-banded Armadillo (Tatu novemcinctus). — By permission of the N.Y. Zodlog. Soc. white fur; the rump is covered with a solid shield of bone, placed nearly vertically and covered with thin scales, and is notched below for the tail, altogether a most exceptional arrangement. Seven or more distinct genera of armadillos are found in the Neotropical region and they display a great range in size; the Giant Armadillo of Brazil (Priodontes) is a yard or more in length, while the little Zaédyus of Patagonia is smaller than a rabbit and, least of all, the Pichiciago is but five inches long. Two families of marsupials occur in South America. The opossums are much more numerous and varied than in North America; three genera and a large number of species, some not larger than mice, range through the forested parts of the continent. Of particular interest is the little Canolestes, THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 191 which has two species, with two enlarged lower front teeth, the sole survivors of a group which is abundantly represented in the Tertiary deposits of Patagonia. The fauna of the Central American subregion is less rich and characteristic than that of the Brazilian and is, to a cer- tain extent, transitional to that of the Sonoran region of North America, several genera proper to the latter region extending into it, which are not known to pass the Isthmus of Panama, such as shrews, a fox and one of the pocket-mice. The West Indian islands are exceedingly poor in mammals, a great con- ‘trast to the East Indian, or Malay, Archipelago; only a few rodents, insectivores and bats occur in them. CHAPTER VII THE SUCCESSIVE MAMMALIAN FAUNAS OF NORTH AND SOUTH AMERICA Tue natural method of telling a story is to begin at the beginning and go on to the end, but to deal in that manner with the many different assemblages of mammals which have in turn inhabited the western hemisphere has the great draw- back of beginning with a time when everything was utterly strange to the modern eye. Could the reader be carried back to the far distant days of the Paleocene epoch, he would find himself in a completely unfamiliar world ; and there is therefore a real practical advantage in reversing the story and starting with the end and thus proceeding gradually from the more to the less familiar. The foregoing chapter gave a sketch of the more striking and characteristic mammals which inhabit the Americas to-day, and we may now take a step backward to the epoch immediately preceding our own, the Pleistocene. As was shown in Chapter V, the Pleistocene was a time of many and great climatic vicissitudes, periods of cold, when the northern part of the continent was buried under great ice- sheets, alternating with far milder periods, when the climate was much as at present, or even warmer. These climatic changes necessitated many changes in the distribution of ani- mals and plants, increasing cold driving them southward, while the return of more genial conditions permitted the northward migration of southern forms. The effects of these changes of climate are still plainly visible in the geographical arrangement of living beings in the northern continents and many anomalies of distribution, otherwise inexplicable, are thus made clear. 192 SUCCESSIVE MAMMALIAN FAUNAS 193 Attention was long ago directed to the fact that the tops of high mountains support a flora and fauna which, on the low- lands, will be found only hundreds, or even thousands, of miles to the northward. The plants which grow on the summits of the White Mountains of New Hampshire recur in Labrador, but not in the intervening area; the vegetation and animals of the high Alps are those of the Arctic regions, and many similar instances might be cited. Hooker and Darwin were the first to find a highly probable explanation of this curious phenomenon by referring it to the climatic changes of the Pleis- tocene epoch. During the last period of cold and glaciation,, the northern plants and animals were driven far to the south and occupied the lowlands along the ice-front and well beyond it; when milder conditions gradually returned, the northern forms not only retreated northward, but also ascended the mountains, as the latter were freed from ice, and thus became cut off as isolated colonies. The general explanation of ‘‘dis- continuous distribution” (see p. 188) is thus always the same, viz., that the intervening regions were once occupied by the forms now so widely separated, which, for one reason or another, have vanished from the connecting areas. I. QuaTERNARY Faunas North America. — The Quaternary faunas of North America are extremely difficult to correlate and place in chronological order, because, for the most part, they are found in locally restricted areas, such as tar-pools, bogs, caverns and similar places. Professor Osborn has, however, succeeded in making an admirable arrangement, which, though it will doubtless be corrected and expanded by future research, represents a most important advance. Of the general problem he says: “The study of the mammals of the Quaternary has by no means progressed so far in America as in Europe; it will be many years before the faunistic succession can be worked out with such chronologic accuracy and precision as has at last been oO 194 LAND MAMMALS IN THE WESTERN HEMISPHERE attained by European geologists and paleontologists.” Ac- cording to Osborn’s arrangement, there are three principal successive Pleistocene faunas, two of which appear to have coincided with interglacial stages, and the third with the last reéstablishment of glacial conditions on a grand scale. Re- garding the details of these faunas, there still remains much uncertainty, and consequently there will be no attempt made here to do more than discriminate between the general Pleis- tocene assemblage, on the one hand, and that of the last cold period, on the other. It must be emphasized that we are as yet unable to assert that all of the animals listed together were actually living at the same time. It is probable that the Pleistocene fossils already obtained give us a fairly adequate conception of the larger and more conspicuous mammals of the time, but no doubt represent very incompletely the small and fragile forms. With all its gaps, however, the record is very impressive; ‘‘the early and mid-Pleistocene life of North America is the grandest and most varied assemblage of the entire Cenozoic Period [i.e. era] of our continent”? (Osborn). There is the. further ad- vantage that the fossils have been gathered over a very great area, extending from ocean to ocean and from Alaska to Central America. Thus, their wide geographical range represents nearly all parts of the continent and gives us information con- cerning the mammals of the great forests, as well as of the great plains. Those divisions of the early and middle Pleistocene which enjoyed milder climatic conditions had an assemblage of mam- mals which, from one point of view, seems very modern, for most of the genera, and even many of the species, which now inhabit North America, date back to that time. From the geographical standpoint, however, this is a very strange fauna, for it contains so many animals now utterly foreign to North America, to find near relatives of which we should have to go to Asia or South America. Some of these animals which SUCCESSIVE MAMMALIAN FAUNAS 195 Fie. 113. — Some of the more characteristic Pleistocene mammals, reduced to a uniform scale, with a pointer dog (in the frame) to show relative sizes. — 1. |Columbian Elephant (Elephas tcolumbi). 2. Giant ¢{Ground-Sloth (+ Megalonyz jeffersoni). 3. tStag-Moose (}Cervalces scotti). 4. tAmerican Mastodon ({ Mastodon ameri- canus). 5. ¢ Giant Beaver (ft Castoroides ohioensis). 6. t Texas Horse (Equus f scotti). 7. tSabre-tooth Tiger (¢ Smilodon californicus). 196 LAND MAMMALS IN THE WESTERN HEMISPHERE now seem so exotic, such as the llamas, camels and horses, were yet truly indigenous and were derived from a long line of ancestors which dwelt in this continent, but are now scattered abroad and extinct in their original home, while others were migrants that for some unknown reason failed to maintain themselves. Others again are everywhere extinct. Most surprising, perhaps, in a North American landscape, is the presence of the Proboscidea, of which two very distinct kinds, the tmastodons and the trueelephants, are found together. Over nearly the whole of the United States and southern Canada, and even with sporadic occurrence in Alaska, ranged: the tAmerican Mastodon (} Mastodon americanus) which was rare in the plains, but very abundant in the forested regions, where it persisted till a very late period and was probably known to the early Indians. This animal, while nearly related to the true elephants, was yet quite different from them in appearance, as will be immediately seen on comparing 1 and 4, Fig. 113, p.195. The most obvious external difference was the comparative shortness of the legs in the tMastodon, which did not exceed and seldom attained a height of 9 ft. 6 in. at the shoulder; the head also was lower and more flattened. The teeth were very different from those of the elephants; the grinding teeth were much smaller and simpler, being low- crowned and rooted and having three or four high, transverse, enamel-covered crests, without cement. The tusks were elephant-like except that in the male there was a single small tusk in the lower jaw, which cannot have been visible exter- nally; this isa remnant of an earlier stage of development, when there were two large tusks in the lower as well as the upper jaw. The creature was covered with long, coarse, dun-coloured hair; such hair has been found with some of the skeletons. . Of true elephants, the North American Pleistocene had three species. Most interesting of these is the northern or Siberian tMammoth (Elephas tprimigenius), a late immigrant from SUCCESSIVE MAMMALIAN FAUNAS 197 northern Asia, which came in by way of Alaska, where Bering Land (as we may call the raised bed of Bering Sea) connected it with Asia. The Mammoth was abundant in Alaska, British Columbia and all across the northern United States to the Atlantic coast. Hardly any fossil mammal is so well known as this, for the carcasses entombed in the frozen gravels of northern Siberia have preserved every detail of structure. It is thus definitely known that the {Mammoth was well adapted to a cold climate and was covered with a dense coat of wool beneath an outer coating of long, coarse hair, while the con- tents of the stomach and the partially masticated food found in the mouth show that the animal fed upon the same vegeta- tion as grows in northern Siberia to-day. The grinding teeth were very high,’ cement-covered, and composed of many thin plates of enamel, dentine and cement, and were closely similar to those of the existing Indian Elephant (LE. maximus). In size this is the smallest of the three Pleistocene species, 9 feet at the shoulder. The {Mammoth was not peculiar to Siberia and North America, but extended also into Europe, where it was familiar to Paleolithic Man, as is attested by the spirited and lifelike carvings and cave-paintings of that date. Thus, during some part of the Pleistocene, this species ranged around the entire northern hemisphere. Closely related to the {Mammoth and in some cases hardly distinguishable from it, is the {+tColumbian Elephant (£. tcolumbi) which, however, attained a considerably larger size, as much as 11 feet, rivalling the largest African elephants of the present time. The head was very high and had a curiously peaked appearance, and the tusks in old males curved inward, overlapping at the tips. From the likeness in teeth and skeleton to the {Mammoth, it may be inferred, though some- what doubtfully, that the {Columbian Elephant was clothed with hair, but not so heavily as the }Mammoth, which was a northern species, the Columbian form replacing it southward, and ranging over the whole United States, including Florida IN THE WESTERN HEMISPHERE LAND MAMMALS 198 : “A104STPT [RINJEN Jo uMasn]A] UBOTIIUTY oY} UI UOJTaYs B WO] (2Qunjoo| spyda7z7) yuRYdel_ urIquMjOD | sy} Jo UOT}eIOYSAY — “FIT ‘SVT SUCCESSIVE MAMMALIAN FAUNAS - 199 and even throughout the table-land of Mexico. The areas of the two species overlapped along the northernmost United States, but are elsewhere distinct. A third species was the huge tImperial Elephant (E. fimpera- tor), the largest of American forms, to which Osborn’s calcula- tions give the almost incredible height of 13 ft. 6 in. This great creature was characterized not only by its enormous stature, but also by the proportionately very large size of its grinding teeth, and was a survivor from the preceding Pliocene epoch ; it is not known to have passed beyond the middle Pleis- tocene and was thus the first of the species to become extinct. In geographical range, the {Imperial Elephant was a western form, extending from the Pacific coast almost to the Mississippi River, east of which it has never been found, and from Ne- braska southward to the City of Mexico. The meaning of this distribution is probably that this elephant shunned the forests and was especially adapted to a life on the open plains. Over most of its area the winters were severe, and this fact makes it, likely that the animal was clothed with hair, but nothing is definitely known on this point. Many other hoofed animals, far more than now inhabit North America, are found in this Pleistocene fauna. The Perissodactyla were represented by horses and tapirs, but not by rhinoceroses; it might seem superfluous to say that there were no rhinoceroses, but, as a matter of fact, that family had a long and varied American history and became extinct only during or at the end of the Pliocene epoch. The horses were extremely numerous, both individually and specifically, and ranged, apparently in great herds, all over Mexico and the United States and even into Alaska. All the known species (at least ten in number) belong to the genus Equus, but the True Horse (£. caballus), to which all the domestic breeds are referred, isnot represented. The smallest known member of the genus is the pygmy #.ttau of Mexico. E.t{fraternus, likewise a very small species, is found especially in the southeast, but 200 LAND MAMMALS IN THE WESTERN HEMISPHERE extended as far north as Pennsylvania and west to Nebraska. On the other hand, E.tgiganteus of Texas exceeded the heaviest modern draught-horses in size and was the largest of the American species; of other Texan forms, one (E.fscotti) resembled Burchell’s Zebra (H.burchelli) in the proportions of head and neck, body and limbs, while another (E.tsemi- plicatus) was more ass-like. The forest horse of the eastern Fic. 115. — A Horse (Equus fscotti) from the older Pleistocene of Texas. Restored from a skeleton in the American Museum of Natural History. states has been named E.fpectinatus, an animal of moderate size. The Great Plains must have been fairly covered with enormous herds of horses, the countless bones and teeth of which, entombed in the Sheridan formation, have given to it the name of ‘“‘Equus beds.’’ The most abundant of the plains species is E.{tcomplicatus, a horse of about 143 hands in height (i.e. 4 feet 10 inches at the shoulder) which also ranged down the Mississippi Valley nearly or quite to the Gulf of Mexico. In California was E.toccidentalis, equalling E.tcomplicatus in size, but with much more simple teeth, and associated with SUCCESSIVE MAMMALIAN FAUNAS 201 it the much larger E.fpacificus, which was inferior only to E.tgiganteus and therefore the second largest of the American Pleistocene horses. To one who knows nothing of the geological history of North America it would be natural to suppose that the Pleis- tocene horses must have been immigrants from the Old World, which failed to establish themselves permanently here, since they completely disappeared before the discovery of the con- tinent by Europeans. This would, however, be a mistaken inference, for. North America was for long ages the chief area of development of the equine family, which may here be traced in almost unbroken continuity from the lower Eocene to the Pliocene. On the other hand, it is quite possible that some of the species were immigrants. Tapirs, which are now confined to southern Asia, Central and South America, were not uncommon in the forested parts of eastern North America as far north as Pennsylvania, but they have not been found west of the Mississippi in the plains region. Two species are known, a larger and heavier one, Tapirusthaysii, and a smaller one which seems to be identical with the living 7. terrestris of Central and South America. ‘Like the horses, the tapirs had a long history of development in North America and may well have originated here, but they withdrew from the continent in the Pleistocene, probably yielding to the last of the glacial advances. There was likewise a much greater variety of Artiodactyla than North America can boast at the present day; some were autochthonous, but, for the most part, they were migrants. from the eastern hemisphere, where the great group of the true ruminants (Pecora) passed through the greater part of its development and where its headquarters still are. Indigenous were the peccaries, or American swine, which still occur from Texas south to Brazil. In Pleistocene time they ranged over nearly all of the United States, as far northward as Pennsylvania, and across the plains to the Pacific coast ; they were represented 202 LAND MAMMALS IN THE WESTERN HEMISPHERE by two genera, now extinct, one of which (ftPlatygonus) had crested grinding teeth and much longer legs than the modern peccaries. Anotherindigenous group, strangeas that may seem, is the suborder (Tylopoda) of the camels and llamas, both of which are represented in the North American Pleistocene, the descendants of a very long American ancestry. Some of these tylopodans were far larger than existing forms, and at least one species extended its range to Alaska. Of ultimately Old World origin, but through a considerable line of descent in America, were the typically American deer (Odocotleus) of which the Virginian and Black-tailed species are familiar modern instances. Whether or not the Old World types, the Caribou (Rangifer) and Wapiti (Cervus canadensis) had reached the western hemisphere, is a matter of some doubt; if present at all, they must have been com- paratively rare. The Moose (Alce americanus), on the other hand, had already appeared, but seems to have been confined to the western half of the continent, its presence in the east being questionable. The mistakenly named “Rocky Mountain Goat” (Oreamnos montanus), which is an antelope of the chamois group, was an apparently late arrival in the Pleistocene, while the peculiar Prong-Buck (Antilocapra americana), which is very different from any of the Old World antelopes, was present in the early part of the epoch. The descent of this remarkable animal is still a problem, but not improbably it was derived from the ‘‘deer-antelopes” of the Miocene and Pliocene, the last of which occurred in the early Pleistocene. Mr. Gidley has announced the surprising discovery in Mary- land of a large antelope hardly distinguishable from the African Eland (Taurotragus). Other late arrivals from the Old World were several forms allied to the existing Musk Ox (Ovibos), at least two genera of which (}Preptoceras and +Eucera- therium) have been found in California. A surprising number of species of Bison occurred in the Pleistocene, no less than seven of which are recognized as distinct, ranging from Florida SUCCESSIVE MAMMALIAN FAUNAS 203 to Alaska. It is not likely that all these species coexisted at the same time, but we cannot yet determine their order of succession, though the modern species, B. bison, was probably the latest to arise. Most of these species were much larger Fic. 116. — Restoration of tPreptoceras, a musk-ox like animal from the Californian Pleistocene. (From a skeleton in the museum of the University of California.) than B. bison, and some were gigantic, such as B.flatifrons, which had a spread of horns of 6 feet and is found through the Mississippi Valley, and B.tcrassicornis of Alaska. Preying upon this great assemblage of hoofed animals was a corresponding array of Carnivora, most of which were in- digenous and derived from American stocks, but there was a considerable migrant element also, such as the bears and badgers. Nearly all the modern kinds of flesh-eaters found 204 LAND MAMMALS IN THE WESTERN HEMISPHERE in the North America of to-day were already here in the Pleistocene, minks, weasels, martens, skunks, otters, badgers, wolverenes, raccoons, foxes, wolves, coyotes, pumas, etc., etc., but there were several others which are either now extinct or no longer to be found in this continent. Of the extinct types much the most striking were the several species of tsabre-tooth tigers (tSmilodon, see Frontispiece) which have been found in the greater part of the United States and no doubt ranged over the whole. These were massive, short-tailed and rather short- legged, but very muscular and powerful, cat-like animals, in which the upper canine teeth were converted into great, recurved, scimitar-like tusks. These large beasts of prey, which about equalled the Leopard in height, but were far heavier, belonged to a group which, at one time or another, spread over nearly the whole world and persisted much later and attained a larger size and higher development in the western hemisphere than in the eastern. They had a very long American ancestry, from the lower Oligocene to the end of the Pleistocene, but the place of their origin is still un- known. In addition to the pumas and lynxes, there were some very large true felines (Felis tatrox and F.fimperialis), which closely resembled the Lion (F. leo) in size, appearance and structure, and have been found in California and the Mississippi Valley ; probably these great cats were immigrants, but they may represent a native development of Miocene and Pliocene stock; the history of the family is too imperfect for a decision of this question. Besides coyotes and wolves which are indistinguishable from existing species, there were some very large wolves, now extinct, of which the commonest and most widely distributed was Canis tdirus (also called C.}indianensis) so abundant in the asphalts of southern California. Bears were not so com- mon in the middle Pleistocene and have not been found in the older part of that epoch, though they probably had already reached North America from the Old World, where they orig- SUCCESSIVE MAMMALIAN FAUNAS 205: inated. Their absence from the older Pleistocene (Equus Beds) may be accounted for by the fact that those beds con- tain a fauna of the open plains, while bears are chiefly forest- living animals. An extinct type of the family is the group of species which constitute the tshort-faced bears ({Arctotherium), very large and powerful creatures, with remarkably shortened jaws, which have been found from ocean to ocean. The smaller beasts of prey, badgers, weasels, etc., were, as intimated above, substantially the same as now. The rodents of the Pleistocene were very nearly in their . modern stage of development, most of the genera and many of the species surviving to present times. Just what members of. the order were introduced from the Old World, the imperfect and fragmentary history will not permit us to say, but some interesting South American immigrants should be noted. One of these, the Capybara or so-called Water-Hog (Hydrocherus capybara), the largest of existing rodents, failed to gain a per- manent foothold, but another South American form, the Short- tailed or Canada Porcupine (Hrethizon dorsatus), common all over the United States in the Pleistocene, has maintained itself to the present day. One especially peculiar form, not derived from South America or the Old World, is the +Giant Beaver (tCastoroides), one species of which, tC. ohioensis, was as large as a Black Bear and occurred in the later Pleistocene, while a smaller species ({C.species indet.) is found in the more ancient deposits of the epoch. In almost all respects tCas- toroides was simply a gigantic beaver, but the grinding teeth were remarkably like those of the South American Capybara (Hydrocherus), so much so that it has been mistakenly re- ferred to the same family by some authorities. By far the strangest elements of the Pleistocene faunas. were the two suborders of gigantic edentates, the {Gravigrada, or tground-sloths, and the tGlyptodontia, which might well be called giant armadillos, if that name were not already in use for a living Brazilian animal. Both suborders are completely 206 LAND MAMMALS IN THE WESTERN HEMISPHERE extinct, but they long played a very conspicuous réle in South America, where they originated and whence the North American representatives migrated. The tground-sloths were great, unwieldy, herbivorous animals covered with long hair, and in one family ({Mylodontide) there was a close-set armour of pebble-like ossicles in the skin, not visible externally ; they walked upon the outer edges of the feet, somewhat as the Ant- Bear (Myrmecophaga) uses his fore paws, and must have been very slow-moving creatures. Their enormous claws may have served partly as weapons of defence and were doubtless used also to drag down branches of trees and to dig roots and tubers. Apparently, the latest of these curious animals to survive was the very large {Megalonyx, which, it is interesting to note, was first discovered and named by Thomas Jefferson. The animals of this genus were very abundant in the forests east of the Mississippi River and on the Pacific coast, much less common in the plains region, where they would seem to have been confined to the wooded river valleys. The still more gigantic t{Megatherium, which had a body as large as that of an elephant and much shorter, though more massive legs, was a southern animal and has not been found above South Carolina. {Mylodon, smaller and lighter than the preceding genera, would seem to have entered the continent earlier and to have become extinct sooner; it ranged across the continent, but was much commoner in the plains region and less so in the forested areas than tMegalonyz, being no doubt better adapted to subsisting upon the vegetation of the plains and less de- pendent upon trees for food. The +Glyptodonts were undoubtedly present in the North American Pleistocene, but the remains which have been col- lected so far are very fragmentary and quite insufficient to give us a definite conception of thenumber and variety of them. It will be better therefore to defer the description of these most curious creatures until the South American Pleistocene is dealt with, as they were incomparably more varied and SUCCESSIVE MAMMALIAN FAUNAS 207 characteristic in that continent. In North America they have been found only in Mexico and the southern United States. The many and great climatic changes which took place in the Pleistocene led to very extensive migrations of mammals from one part of the continent to another, as the conditions of temperature and moisture changed. In Interglacial stages, when the climate was much ameliorated, southern species spread far to the north, as when the {Mastodon ranged into Alaska, and the Manatee, or Sea-Cow, of Florida waters, came up the coast to New Jersey, while the increasing eold of on- coming glaciation caused a reverse movement and drove northern and even Arctic forms far to the south. Thus, the Musk-Ox, the Caribou and the northern {Mammoth came south beyond the Ohio and the Potomac, and the Walrus was found on the South Atlantic coast. Itis these migrations which give such a mixed character to the Pleistocene faunas from the climatic point of view, as it is often very difficult to correlate or synchronize the fossiliferous deposits with the Glacial and Interglacial stages, though this has been definitely accomplished in several very important instances. The latest of the Pleistocene faunas is less completely known than those of the earlier and middle portions of the epoch, for but few localities have yet been discovered with any extensive series of fossils. As worked out by Osborn, this fauna coincided with the last Glacial stage and was a greatly reduced and impoverished assemblage as compared with those of the middle and lower Pleistocene, though it is not safe to argue that all the animals not found in this fauna were already extinct, for the known list is still far too short to be entirely representative. The American {Mastodon (tMastodon ameri- canus, see p.196) was still abundant in the forested regions and was apparently able to withstand severe winter temperatures, as certainly was the {Mammoth (Hlephas tprimigenius, see p. 196), which was so abundant in the coldest part of Siberia and which extended south to the Potomac, presumably at this 208 LAND MAMMALS IN THE WESTERN HEMISPHERE time. Horses were still present in North America, though apparently in greatly diminished numbers and variety. Tapirs have not been found, though they may have lingered on in the southern regions. The typically North American genus of deer (Odocoileus) was, of course, well represented, and Old World types had a much more southerly distribution than at present. The Caribou (Rangifer caribou) came down into Pennsylvania and Ohio, the Moose (Alce americanus) into Kentucky and Kansas, and the Wapiti (Cervus canadensis) is reported as far south as Florida. A very remarkable animal is the Stag- Moose ({Cervalces scotti), the best preserved skeleton of which is that in the museum of Princeton University. This was found in a shell-marl beneath a peat-bog at Mt. Hermon, N. J., north of the great terminal moraine, and therefore most probably this particular individual dates from a time not earlier than the beginning of the final retreat of the ice. {Cervalces, as its name implies, was in some respects inter- mediate between the Stag (Cervus) and the Moose (Alce); in general proportions it most nearly resembled the latter, having a short neck, long body and very long legs; but the skull differed in many respects from that of the Moose, especially in parts which show that the great, inflated snout and pre- hensile upper lip had no such development in the extinct as in the living form. The antlers were unique among the known members of the deer family, resembling those of the Moose, though much less palmated and with the addition of great trumpet-shaped plates. The feet were large, almost as large as in the Caribou, and the whole structure indicates an animal well fitted to travel through deep snows and flourish in severe winters. Even more typically northern than the Caribou were the Musk-Oxen, of which two genera occurred in the late Pleistocene. One of these, tSymbos, is extinct and was characterized by its short horns; the other, Ovibos, is the genus to which the exist- ing species, O. moschatus and O. wardi, belong and is now con- 209 MAMMALIAN FAUNAS SUCCESSIVE ‘APISIOATU A) UOJOUTIG JO WNASNUL oY} UI UOJTOYS B WOLF PaIOySar ‘27,098 saapvasa,J| — "PTT “OI - Tres sTIWI/Sd0n ZANT aE ER 210 LAND MAMMALS IN THE WESTERN HEMISPHERE fined ‘to the extreme north of the continent, the Arctic islands and Greenland. The remains of Musk-Oxen have been found mostly along the great terminal moraine which marks the front of the last ice-invasion, but they occurred also as far south as Oklahoma, and in Utah they ranged far to the south of the ice-front. Nothing could be more conclusive evidence of a climate much colder than the modern one than the presence of Caribou and Musk-Oxen in the United States and of the Walrus on the coast of Georgia. The smaller animals were much as they are now, differing only in range. The tsabre-tooth tigers, the last of a most interesting line, persisted in the south, and an extinct genus of skunks has been discovered in Arkansas, but otherwise the Carnivora were entirely modern in character. Unfortunately, these smaller animals are very incompletely known, much the richest aggregation which has yet been found being that collected by Mr. Brown in the Conard Fissure, Arkansas. From this collection Mr. Brown has described thirty-seven genera and fifty-one species of mammals, of which four genera and twenty-four species are extinct. That is to say, less than one-ninth of the genera and one-half of the species represent extinct forms. Contrast this with the middle Pleistocene assemblage found in the Port Kennedy cavern in eastern Penn- sylvania, of sixty-four species with at least forty extinct ones. The foregoing sketch, brief and imperfect as it necessarily is, makes it sufficiently plain that North America during the Pleistocene was far richer in mammalian life than it was when the continent was first settled by Europeans. When we make the proper allowance for the many forms which undoubtedly remain to be discovered and for those which may have vanished without leaving a trace behind them, the. contrast becomes all the more striking. Not only did Pleistocene North America have substantially all the mammals that it. now possesses, but it had many more. The lions and fsabre-tooth tigers, the gigantic tshort-faced bears, the tapirs and many varieties of SUCCESSIVE MAMMALIAN FAUNAS 211 horses, large and small, the camels and llamas, many species of bisons, some of enormous proportions, several forms allied to the Musk-Ox, the elephants and ftmastodons, the tgiant beavers and South American water-hogs, the huge tground- sloths and {glyptodonts, have all disappeared, leaving a con- tinent, that, by contrast, is “zodélogically impoverished.” The Pleistocene fauna was strangely mixed in character, the free roads of migration bringing together Old World and South American types, and mingling them with indigenous forms in a cosmopolitan assemblage. Turning to South America, we find in the pampas of Argen- tina a wonderful museum of Pleistocene mammals, such as occurs nowhere else in the known world, and this is supple- mented by the very rich collections gathered from the caverns of Brazil and from deposits of Ecuador and Bolivia, and thus all the important regions of the continent, save the far south, are well represented. These faunas are far stranger than the corresponding ones of North America and differ more radically from those of modern times, since they include a much larger proportion of extinct types, and the extinctions have swept away not only species and genera, but families and orders as well. The South American Pleistocene assemblage of mammals is very clearly divisible into two elements: (1) the immigrants from the north, which reached the southern continent in suc- cessive waves of migration, that have left records of themselves as early as the older Pliocene, perhaps even the upper Miocene, and (2) the indigenous element, which had a very long history of development in South America. To the immigrant class be- longed all of the Carnivora, which therefore resembled their North American relatives, but were less varied in character. Of the bears, only the huge, tshort-faced kind (}Arctotherium, Fig. 275, p. 549) are known, and it is not likely that true bears existed except in the Andes, as is also the case to-day. Of the cat family, the tsabre-tooth tigers ({Smilodon) were as common in 212 LAND MAMMALS IN THE WESTERN HEMISPHERE South America as in North, and, while there were no lions, there were large cats nearly allied to the Jaguar and Puma, and smaller ones, like the Ocelot. The dogs were quite numerously Fic. 118.—Some of the commoner Pampean mammals, reduced to a uniform scale, with a pointer dog (in the frame) to show the relative sizes. 1. + Dedicurus clavi- caudatus. 2. tGlyptodon clavipes, tglyptodonts. 3. tMacrauchenia patachonica, one of the ¢ Litopterna. 4. {Pampas Horse ({ Hippidion neogeum). 5. + Toxodon burmeisteri, a ttoxodont. 6. +Megatherium americanum. 7. t Mylodon robustus, + ground-sloths. represented by species resembling closely the existing South: American fox-like wolves and the Bush-Dog (Icticyon) and, strange to say, by one which seems referable to the same SUCCESSIVE MAMMALIAN FAUNAS 213 genus (Cyon) as the Dhole of India. The weasel family (Mustelidz) were less numerous and varied than in the northern continent, as they still are; coatis (Naswa) and raccoons (Procyon) were abundant and one species of the latter was much larger than any existing one; extinct species of skunk (Co- nepatus), tayra (Tayra) and otter (Lutra) were also present, but the badgers, minks, martens and wolverenes were not. The hoofed animals were represented by a great variety of forms, both immigrant and indigenous, of which the latter belonged to orders now entirely extinct. Horses were com- mon in all parts of the continent, where fossils of this epoch have been obtained, and are referable to two very distinct groups: (1) to the typical genus Equus, of which three species have been described, all somewhat more primitive than the True Horse (#. caballus) and, like most of the Pleistocene species of North America, with a certain resemblance to the zebras and asses; (2) to an extinct group of four genera, the best known of which is tHippidion. The species of this genus (which has also been reported from North: America, though upon hardly sufficient evidence) had most exceptional characters in the skull, and the head was relatively large and clumsy, with narrow and very high facial region. The neck was com- paratively short, the limbs heavy and the feet short. These animals can hardly have been very swift runners. A very interesting member of this group is tHyperhippidium, a small horse found in the Andes, with remarkably short feet, well adapted for a mountain life. The only other perissodactyls were tapirs, which ranged down to the Argentine pampas, much farther south than now. The Artiodactyla were much more varied; there were peccaries, many species of llamas, which then extended into Brazil, and were not confined, as at present, to the colder portions of the continent. There were also numerous deer, all of the South American type, and two different antelopes have been reported, though that family has no representatives LAND MAMMALS IN THE WESTERN HEMISPHERE 214 “soily souong ‘umMasn]] [BUOTZE NY OY} UI UOJo[aYS B WOT paloysay *(wnaHHoau uorpiddry7|) as1oyy sedureg VW — ‘611 ‘DS SUCCESSIVE MAMMALIAN FAUNAS 215 in the southern continent now. Several species of tmastodons have been found in Brazil, Argentina, Bolivia and elsewhere, but none of the true elephants. Why the fmastodons were able to make their way into South America, while the elephants were not, is one of the puzzling questions of mammalian dis- tribution to which no answer can be given. All the preceding types of hoofed animals, the horses, tapirs, peccaries, llamas, deer, antelopes and tmastodons were migrants from the north, and four of these, tapirs, peccaries, llamas and deer, were able to gain a permanent footing in South America and are more or less abundant there to-day, while the horses, antelopes and tmastodons failed to do so and died out. In addition to these, there were the indigenous types, which are now extinct and have never been found out- side of the Neotropical region. An extremely peculiar creature, {Macrauchenia, was the last surviving member of an order, the {Litopterna, which for ages played a very important réle in South America. {Macrauchenia was a large animal, somewhat larger and of much heavier build than a camel, to which it had a considerable, though entirely superficial, resemblance. The head was relatively small and must have had quite a long proboscis; the neck was very long, suggesting that the animal browsed upon trees, which is also indicated by the character of the teeth; the legs were long and stout, the feet short and each provided with three toes. Another curious creature was +Typotherium, from which is named the group of the {Typo- theria, which some authorities regard as a suborder, while others assign to it a full ordinal rank. The {Typotheres throughout the Tertiary period were among the most abundant and characteristic of the South American hoofed animals, and the genus +Typotherium was the last of a very long series and was an animal of moderate size, with chisel-shaped incisor teeth so like those of the rodents that the genus was long referred to that order. Finally, we have tToxodon, type of the order {Toxodontia, a ponderous LAND MAMMALS IN THE WESTERN HEMISPHERE 216 jo UINasny]] OY} UI UOJsJayS & WIOIJ par0ysoy *BYR1_q BT *(wovuoyon} od viwayond.oD py |.) UI9ydopT| uvadueg YW — ‘OZI “D1 SUCCESSIVE MAMMALIAN FAUNAS 217 beast, as large as a rhinoceros, which, there is some reason to think, was largely aquatic in its habits. The first species of this extraordinary creature was found by Charles Darwin, who says of it: ‘‘Perhaps one of the strangest animals ever discovered ; in size it equalled an elephant or megatherium, Fic. 121.— A Pampean t Toxodont (¢Tozodon burmeisteri). Restored from a skeleton in the La Plata Museum. but the structure of its teeth, as Mr. Owen states, proves indisputably that it was intimately related to the Gnawers [v.e. Rodentia] . . . in many details it is allied to the Pachy- dermata: judging from the position of its eyes, ears, and nostrils, it was probably aquatic, like the Dugong and Manatee, to which it is also allied.””! Modern views concerning the relationships of | 7’oxodon are very different from those advanced by Darwin, but he gives a vivid picture of its diverse likenesses. Neither }Macrauchenia, tTypotherium nor {Toxodon has been 1Voyage of a Naturalist, Am. ed., 1891, p. 82. 218 LAND MAMMALS IN THE WESTERN HEMISPHERE found in the Brazilian caverns, but this is no doubt due to the accidents of preservation, for the latter animal ranged north to Nicaragua. The rodents likewise were partially of immigrant and par- tially of native stock. To the former belonged the few mice and rats and a meadow-mouse (Microtus), a group not repre- sented in present-day South America, and a rabbit. Very much more abundant and varied were the indigenous forms, all of which belonged to existing families and most of them to exist- ing genera ; the tree-porcupines, cavies, agoutis, spiny-rats, viz- cachas, capybaras, coypus, etc., were abundantly represented, for the most part by extinct species. The monkeys were of purely Neotropical type and several modern genera, such as Cebus and Callithrix, and one very large extinct genus, tProtopithecus, of the same family, have been found in the caverns of Brazil, but not in the pampas of Argentina, which would seem to have been a country of open plains. In the South America of to-day one of the most striking and peculiar elements of the fauna is that formed by the Eden- tata, the sloths, anteaters and armadillos, and this was even more true of the same region in Pleistocene times. Anteaters and sloths are very scantily represented, but this is merely an accident of preservation; armadillos, on the other hand, were very numerous both in Brazil and in Argentina, and, in addition to many modern genera, there were several which are no longer in existence, such as tChlamydotherium, which was a huge creature almost as large as a rhinoceros. Then there were the two extinct suborders of the tglyptodonts (tGlyptodontia) and the fground-sloths (tGravigrada) which were astonishingly abundant in Argentina and which, as was shown in a previous page (p. 205), were also well represented in North America. Few more fantastic-looking mammals than the tglyptodonts have ever been found; the short, deep head, with its. shield SUCCESSIVE MAMMALIAN FAUNAS 219 of thick, bony plates, the huge carapace made up of innumerable plates of bone firmly united at their edges and without the movable bands of the armadillo carapace, the enormous tail- sheath, the short legs and massive feet with broad hoofs, must have given these animals rather the appearance of gigantic tortoises than of mammals. The fglyptodonts were especially numerous and varied in the Argentine pampas, and a stately array of them is mounted in the museums of La Plata and Buenos Aires; in length, they ranged from six to twelve feet, including the tail. The skeleton and carapace did not differ very greatly in appearance among the various genera, but there were great differences in the form and size of the bony sheath enclosing the tail. In the genus {Glyptodon the sheath was composed throughout of movable overlapping rings, with prominent spines on them; in fSclerocalyptus the hinder half of the sheath coalesced into a single piece, marked only by the elaborate ornamentation of the horny scales, while in {Dedicurus the end had a tremendous, club-like expansion, which must have been set with great horn-like spines. The tglyptodonts were ponderous, slow-moving and _ inoffensive plant-feeders, almost invulnerable to attack, and probably used their massive tails, which could be freely swung from side to side, as redoubtable weapons of defence, much as the alli- gator uses his tail. In comparison with the bewildering variety in South America, the few that made their way into North America were quite insignificant. Much the same statement applies to the tground-sloths, and though these ranged far more widely through the northern continent than did the tglyptodonts, they were but few in comparison with the multitude which inhabited alike the forests of Brazil and the plains of the south. Two of the three genera of tground-sloths which occur in the North American Pleistocene, +Megatherium and tMylodon, are also found in South America; and though tMegalonyx has not yet been ob- tained there, the family of which it is a member was represented. LAND MAMMALS IN THE WESTERN HEMISPHERE 220 ‘eYBIq wT Jo wnosnyy dU} Ul UOJOOYS B WOT poloysoy -(~nuvoWaWD wnIsay)DOe TY 1) YqiOls-punoin| uvodurrg onuess y— ‘zz ‘pig SUCCESSIVE MAMMALIAN FAUNAS 221 In size, these creatures varied from a tapir to an elephant, though all were much shorter-legged than any elephant; the extremely massive tail, which the larger forms had, served to support the huge body, when erected to tear down the branches and leaves upon which these strange creatures fed. Opossums were extremely numerous, especially in the Brazilian caves, where in half a cubic foot of earth 400 jaws were collected. The Pleistocene mammalian fauna of South America was a mixture of modern forms with ancient, vanished types similar to that which we found in North America. The fground- sloths and fglyptodonts, the flitopterns, ftoxodonts and {typotheres, the antelopes, horses and fmastodons have all disappeared from the continent, or vanished altogether from the face of the earth. Il. Tertiary Faunas 1. Pliocene North America. — No part of the Cenozoic history of North America is so imperfectly recorded and so unsatisfactorily known as that of the Pliocene, and the later portion of that epoch is especially obscure. If the Peace Creek formation of Florida is properly referred to the upper Pliocene, it would show that the mammals of that time were substantially the same as those of the early Pleistocene. The only fauna, as yet discovered, which can be referred to the middle Pliocene, is that of the Blanco beds of north- western Texas, which have yielded but a scanty list of mostly ill-preserved fossils. Obviously, these give us a very incom- plete picture of the life of that time. The great fground- sloths had already reached North America, and the genus +Megalonyx, so common in the forested areas of Pleistocene North America, was perhaps already in existence. The tglyptodonts were likewise represented by one genus ({Glyp- 222 LAND MAMMALS IN THE WESTERN HEMISPHERE totherium) which was distinguished by the simple rings of the tail-sheath. No rodents have yet been found and only a few of the Carnivora, though a large cat, a musteline and a large {‘‘bear-dog”’ are known. There were no true elephants, but several species of tmastodons, all of which were different from those of the Pleistocene; and in some, grinding teeth, though still low-crowned, had become much larger and more complex, marking a stage of advance toward the elephan- tine dentition. Horses of primitive type, the feet having three functional toes instead of one, were relatively abundant. Very large llama-like animals were present, but nothing has been ascertained with regard to the deer and antelopes of the time, and the only other representative of the Artiodactyla yet recovered is a peccary, interesting as being a species of the genus ({Platygonus) which became so abundant and wide- spread in the Pleistocene. Scanty and incomplete as this fauna is, it suffices to show that the middle Pliocene mammals were much more primitive than those of the Pleistocene. The fauna of the Snake Creek formation in western Nebraska and that of the presumably somewhat later beds of northwestern Nevada, which are referable to the lower , Pliocene, may be considered together. The rodents, which are not very fully represented, were quite modern in character and belonged mostly to extinct species of modern genera, such as hares, pocket-gophers, beavers, forerunners of the tGiant Beaver, marmots, sewellels, etc. A remnant of a more ancient world, especially characteristic of the Miocene, is found in the remarkable burrowers, the horned tmylagaulids which have been extinct since the lower Pliocene. Carnivora were abundant, and members of all the families which inhabit North America to-day have been obtained; wolves, t‘‘bear- dogs,”’ t‘‘hyena-dogs”’ and forms like the Dhole of India were common. The terms }‘‘bear-dogs” and f‘‘hyena-dogs”’ are not to be understood as implying any relationships of these animals to bears or hyenas, but merely a certain superficial SUCCESSIVE MAMMALIAN FAUNAS 223 resemblance; these were very large members of the dog family (Canide), now extinct. Mustelines, large and small, are found, and possibly some bears had already made their way from the Old World, but this is still uncertain. fSabre-tooth tigers and true cats, some as large as lions and one species fairly gigantic, were likewise characteristic of the time. There Fic. 123. — tHorned Gopher (tEpigaulus hatcheri), lower Pliocene, Nebraska. Restored from a skeleton in the U.S. National Museum. was a great wealth of horses, though the modern genus Equus was not among them; all the genera are now extinct and all were three-toed. Several distinct phyla were represented, some progressive and advancing toward the modern forms, others conservative and stationary. Browsing horses with low-crowned teeth, grazing horses with prismatic, cement- covered teeth, heavier and lighter, larger and smaller, must have covered the plains and thronged the woods. Ancestral tapirs were present, though far less common. A family which 224 LAND MAMMALS IN THE WESTERN HEMISPHERE seems to be utterly exotic to North America, that of the rhinoc- eroses, was present, and of these there were three or four series, mostly without horns, or with a very small horn on the tip of the snout. The extremely aberrant perissodactyls (tAncylo- poda), in which the hoofs were converted into great claws, perhaps persisted, but the evidence is not conclusive. The Artiodactyla were, for the most part, totally different from those of modern times, though several forms were an- cestral to some now living. Peccaries more primitive than the living genus were the only representatives of the swine- like suborder; ancestral camels and llamas were among the commonest of the hoofed animals and an extinct phylum, that of the {‘‘giraffe-camels” ({Alticamelus) continued over from the Miocene. The giraffe-camels are so called, not because of any actual relationships with the giraffes, but on account of certain likenesses in the proportions of the animals compared. {Alticamelus was a very large, camel-like creature, with remark- ably elongate neck and limbs and comparatively small head, which no doubt resembled the giraffes in browsing upon trees which were above the reach of the ordinary camels and llamas of the time. It was the terminal member of a series, or phylum, which branched off from the main stock in Oligocene times and pursued a course of development which was independent of the principal series, but curiously parallel with it. The deer of the lower Pliocene were little, graceful creatures ({Blastomeryx) which had no antlers, but the males were armed with sabre-like upper canine tusks, so that they must have resembled the Musk-Deer of Tibet, but were smaller and more slender. The remarkable group of t‘‘deer-antelopes,”’ now extinct, was represented by jMerycodus, a dainty little creature, less than two feet high at the shoulder, which had the antlers and general appearance of a small deer, but the high-crowned grinding teeth which most antelopes have. True antelopes of two different lines were also present, though they are as yet known from little more than the bony horn-cores; of these, SUCCESSIVE MAMMALIAN FAUNAS 225 one is the flat-horned and the other the twisted-horned or strepsicerine type, such as is illustrated by the Eland and Kudu of modern Africa. The latter may, however, be related to the peculiarly North American Prong-Buck (Antilocapra) and not to the strepsicerine antelopes of the Old World. The last survivors of an exclusively North American family, the toreodonts, which were wonderfully numerous and varied from the upper Eocene onward, are found here. The tmastodons (tGomphotherium) of this formation had well-developed tusks in the lower as well as in the upper jaw, and in one species the chin-region or symphysis of the lower jaw was greatly prolonged, an ancient feature. That the South American edentates had already reached the northern continent is sufficiently proved by remains of fground-sloths, which are, however, too incomplete to permit identification of the genus. {Glyptodonts have not yet been found, but this fact does not demonstrate that they had not accompanied the fground-sloths in their migration, for at no time did they range so far north as Nebraska or northwestern Nevada, and the only mammal-bearing formation of lower Pliocene date known in the south, the Alachua Clay of Florida, has yielded too scanty a list of fossils to make its negative evidence at all conclusive on this point. The mammals of the middle and especially of the lower Pliocene were much stranger and more primitive than might be inferred from the foregoing brief account. Except several of the Rodentia and perhaps one or two of the Carnivora, the genera are all extinct and such familiar terms as horses, rhinoc- eroses, camels, etc., can be employed only in a very compre- hensive sense, as equivalent to families. The Pliocene of South America is involved in some obscurity ; not that there is any question as to the formations, or their order of succession, but there is much doubt as to the limits of the epoch both above and below. The latest Pliocene fauna, that of the Tarija Valley in Bolivia, was essentially the @ 226 LAND MAMMALS IN THE WESTERN HEMISPHERE same as that of the Pleistocene and contained a similarly large proportion of migrant elements from the north, but it was evi- dently older and many of the species were different. The two divisions of the Araucanian fauna, contained in the beds of Catamarca and Monte Hermoso respectively, are very much alike and need not be given separate consideration. In one respect these presumably upper Pliocene faunas formed a very strong contrast to the mammalian assemblage of the Pleistocene, and that is in the quite insignificant part taken-by the migrants from North America. Of the Carnivora there were but two representatives, one referable to the raccoon family and one to the dogs, while a hare and a small member of the Artio- dactyla, of indeterminate family, complete the list of northern forms, though this list will doubtless be extended by future discovery. The peccaries, deer, antelopes, tapirs, horses, tmastodons, cats, weasels, otters, squirrels, mice, etc. had not reached the southern continent, or were still so rare that remains of them have not been found. This rarity and relative insignificance of the northern forms gave a very different aspect to the fauna. On the other hand, the indigenous South American groups were very fully represented. Many kinds of opossums and a few large carnivorous types, much like the so-called Tas- manian Wolf (Thylacynus), were the remnants of a much larger assemblage of marsupials which inhabited South America in the Miocene. Of the Edentata, there were great abundance and variety, many large tglyptodonts and some gigantic armadillos, as well as numerous examples of normal size; the tground-sloths, though somewhat smaller than those of the Pleistocene, were mostly of gigantic size, and true or arboreal sloths (Tardigrada) have been reported. The very numerous rodents, with the exception of the intrusive hare, all belonged to typically South American families. Some of the rodents were gigantic and one ({Megamys), a member of the Chinchilla family, was equal to a rhinoceros in size and SUCCESSIVE MAMMALIAN FAUNAS 227 the largest known representative of the order. Especially characteristic was the abundance of the cavy family (Caviide). The hoofed animals, with the single known exception of the immigrant artiodactyl, all belonged to the autochthonous orders, all of which are extinct at the present time. Fore- runners of the extraordinary genus |Macrauchenia, which was one of the most conspicuous elements of Pleistocene life, were quite common in the Pliocene and differed from the Pampean genus chiefly in their smaller size and less advanced specializa- tion. We find here also the last survivors of another family of the fLitopterna, the tproterotheres ({Proterotheriide), which imitated the horses in such a surprising manner that some authorities believe them to have been actually related to those perissodactyls. ‘The Monte Hermoso genus (t+Epitherium) had feet which were wonderfully, though but superficially, like those of the three-toed horses. The +Toxodonta were numerous and most of them were large, ponderous animals; one genus (t7'ri- godon) had the interesting peculiarity of a single median horn on the forehead, much like that of a rhinoceros. Horned spe- cies were always rare among the indigenous groups of South American ungulates, and all that have been discovered so far belonged to the ttoxodonts. The remaining group, that of the tTypotheria, was also well represented, both by larger and by very small forms, some no larger than a rabbit (tPachyru- khos). The presumably lower Pliocene (perhaps upper Miocene) fauna of the Parand4 formation is as yet known only from very fragmentary material. Representatives of the dogs, raccoons and bears have been reported, but the identifications are doubt- ful; at all events, these would seem to have been the most ancient of the northern immigrants. A considerable number of marsupials, both opossums and large predaceous types, have been found. The rodents were very numerous, all belonging to South American families and some of them very large. The edentates were gigantic tground-sloths and tglyp- 228 LAND MAMMALS IN THE WESTERN HEMISPHERE todonts, with numerous armadillos of ordinary size. The hoofed animals all belonged to the indigenous South American orders, the predominant place being taken by the {toxodonts, Fic. 124. — Head of Horned tToxodont (tTrigodon gaudryi). Pliocene of Monte Her- moso. Restored from a skull in the Ameghino collection. some of which were large. There were many ftypotheres, both of the larger and smaller kinds. The jLitopterna were represented both by the horse-like tproterotheres and the long- necked tmacrauchenids, the latter smaller and less specialized than those of the Pampean. SUCCESSIVE MAMMALIAN FAUNAS 229 2. Miocene North America. — Upper Miocene beds cover extensive areas of the Great Plains region and are scattered from Mon- tana far into Mexico. The rich fauna is an outgrowth and development of that of the middle Miocene, with but few im- migrant additions and, on the other hand, passes so gradually into that of the lower Pliocene, that any line of separation between them is very difficult to draw. The rodents, numerous as they are among the fossils, are almost certainly very incom- pletely represented in the collections; the families are almost all still in existence, but nearly every genus is extinct, and thus the vernacular names used to designate them must be under- stood in a broad sense. Hares, mice, pocket-gophers, squirrels, marmots, beavers and the extraordinary tmylagaulids were all abundant. In even more strongly marked sense must the broad mean- ing for the vernacular names of the other mammals be em- phasized, for we have to deal almost exclusively with extinct genera, which differed much from their modern descendants. Many of the Carnivora have been obtained; there were numerous dogs, some rivalling the largest of existing bears in size, true felines and tsabre-tooth tigers, which were smaller and lighter animals than the great beasts of the Pleistocene ; weasels, martens, otters and raccoons, but no bears, The bears, a family of Old World origin, are not certainly known in America before the Pleistocene, but had probably reached this continent in the Pliocene. . As is so very generally true, the commonest and _ best- preserved of the fossils are those of the hoofed animals. The fmastodons were of the four-tusked kind ({Gomphotherium or +Trilophodon), the skull and teeth of which differed so markedly from those of the true elephants. The relatively small, low- crowned and simple grinding teeth were common to all the ftmastodons, but the tusks were different from those of the 230 LAND MAMMALS IN THE WESTERN HEMISPHERE larger members of the group. The upper tusks were compar- atively short and nearly straight and retained a band of enamel, while the lower tusks were still shorter, chisel-shaped and so worn as to prove that they were regularly used, no doubt in cropping leaves; the shortness of these lower tusks was com- pensated for by the great elongation of the lower jaw. The R- BRUCE NORJFALL_ 2 “O'R ~ Fig. 125.—tTeleoceras fossiger, a short-legged rhinoceros, with small nasal horn; lower Pliocene and upper Miocene of Nebraska. Restored from a skeleton in the American Museum of Natural History. head was proportionately broad and low and, for Proboscidea, these were small animals, not more than five or six feet high at the shoulder. The body, limbs and feet had already at- tained substantially their modern grade of structure, advance among the Proboscidea being chiefly restricted to the teeth and skull. _ Four families of Perissodactyla were represented in the upper Miocene. The rhinoceroses, which were very abun- dant, were present in considerable variety ; some were hornless, others had a single small horn on the end of the nose. Among these rhinoceroses there was much difference in bodily pro- SUCCESSIVE MAMMALIAN FAUNAS 231 portions, some being extremely heavy, with very short legs and feet, and these were the commonest, while others had longer legs and less massive bodies. Tapirs, on the contrary, would seem to have been scantily represented; at least, they are rare among the fossils. The extraordinary, aberrant tchalicotheres, perissodactyls with claws instead of hoofs, still persisted, but are far better known from the lower Miocene, in connection with which they will be described. The domi- nant perissodactyl family was that of the horses, of which no less than five genera are already known. There were some with very low-crowned teeth, which must have fed principally by browsing upon leaves and such soft diet ; but the grazing kinds, which had high-crowned, cement-covered and very complex grinding teeth, had come to the fore. Still retaining three toes in each foot, with the middle toe so en- larged as to bear nearly the entire weight, save in snow or soft ground, these eminently cursorial animals, which had the slender limbs of a deer, must have roamed the plains in great herds. Still commoner were the Artiodactyla. Many species of grazing camels, which were the predominant artiodactyl family in North America during upper Miocene times, were the ancestors both of the true camels of the Old World and the South Americanllamas. }Giraffe-camels havenot yet been found and no doubt they were much less abundant than in the middle Miocene, but that they had not completely disappeared is shown by their recurrence in the Pliocene. As compared with earlier ages, the toreodonts had begun a rapid decline and had lost notably both in numbers and variety, but one most curious beast ({Pronomotherium, Fig. 197, p. 375) marked the final step in the development of the short-faced, proboscis-bearing series, which may be traced back to its beginnings in the Oligocene. In this wonderful creature the skull was so short and deep as to suggest that of a gorilla or some other great ape. No other artiodactyls even approximate these later proboscis-bearing 232 LAND MAMMALS IN THE WESTERN HEMISPHERE toreodonts in the altogether exceptional formoftheskull. Graz- ing toreodonts ({Merychyus), of moderate and small size with high-crowned teeth, were evidently quite common on the upper Miocene plains. The thornless deer and f‘‘deer-antelopes” Fic. 126. —+tProcamelus elrodi, a large camel from the upper Miocene. Restored from specimens in the Carnegie Museum. differed but little from those of the lower Pliocene. Peccaries were fairly abundant. The upper Miocene fauna was especially characterized by the large number of mammals, belonging to several different orders, which had acquired the high-crowned, persistently growing pattern of grinding teeth. Many of the horses, camels, ruminants and rodents displayed this structure, and, SUCCESSIVE MAMMALIAN FAUNAS 233 as was first pointed out by Kowalevsky, the explanation is probably to be found in the spread of grassy plains at the ex- pense of the forests. On account of the silica which they contain, the grasses are very abrasive and rapidly wear the teeth down. In adaptation to this new source of abundant and nutritious food, many kinds of mammals developed a form of tooth which was fitted to compensate by growth for the loss through abrasion. The middle Miocene, small areas of whichoccur in Montana, eastern Oregon and northeastern Colorado, has received various local names, the typical one being the Deep River of Montana. Very probably, these scattered areas are not strictly contem- poraneous, but form a closely connected series. That a land- connection with the eastern hemisphere existed, is made clear by the appearance of several unmistakably Old World types of animals and the beginnings of migration from South America are perhaps also to be noted, though this cannot be positively stated. The evidence for the South American connection is the finding in the middle Miocene of Oregon of what are believed to be the earliest remains of tground-sloths yet dis- covered in North America, but the material is too scanty for altogether certain determination. . The smaller animals are not very well represented in the middle Miocene faunas, as conditions appear to have been unfavourable to their preservation; something is known of them, nevertheless. The very curious extinct family of rodents known as the tMylagaulide, the presence of which was noted in the upper Miocene and lower Pliocene, first appeared here. These jmylagaulids, which were distantly related to the modern Sewellel (Aplodontia rufa), were characterized by the great enlargement and complication of one of the grinding teeth in each jaw and the consequent reduction of the others. One genus of this family, asin the Pliocene, had the peculiarity, unique among rodents, of developing a large horn upon the nose, like a miniature rhinoceros. Among the Carnivora, we find a 234 LAND MAMMALS IN THE WESTERN HEMISPHERE great variety of dogs, large and small, all belonging to extinct genera, as indeed is true of the other carnivores also. True felines have been found, but as yet, none of the tsabre-tooth series ; the abundance of the latter, however, in both preceding and succeeding formations, is sufficient proof that the discovery of them in the middle Miocene is merely a question of time. Mustelines were present, and especially noteworthy is the appearance of the first American otters, immigrants from the Old World. Of the hoofed animals, the most interesting are the Pro- boscidea, the most ancient of which that are definitely deter- minable in America occur in this horizon. The place of origin and ancestry of these animals were long exasperating puzzles. Appearing suddenly in the Miocene of Europe and North America, in which regions nothing was known that could, with any plausibility, be regarded as ancestral to them, they might as well have dropped from the moon, for all that could be told concerning their history. The exploration of the Eocene and Oligocene beds of Egypt has dispelled the mystery and shown that Africa was the original home of the group, whence they gradually spread to every continent except Australia. Little is known of these earliest American pro- boscideans, but they were doubtless small tmastodons of the four-tusked type. Among the Perissodactyla, the rhinoceroses were perhaps the most conspicuous; the native American stocks of this family appear to have mostly died out and to have been replaced by two or more phyla of immigrants from the Old World, some of which were hornless, others had a small horn on the tip of the nose and others again had a second and smaller horn on the forehead. Tapirs, though unquestionably present, are rare as fossils and not well known. Several distinct phyla of horses may be distinguished, which were like small ponies in size, but of more slender form; they were all three-toed, but there were marked differences among them with regard to the degree SUCCESSIVE MAMMALIAN FAUNAS 235 to which the middle toe (the third of the original five) had been enlarged to carry the whole weight and the lateral toes (second and fourth) reduced to mere ‘‘dew-claws.’’ While browsing horses, with low-crowned teeth, still persisted in large numbers, we find also the extremely interesting beginnings of the highly complex, cement-covered and high-crowned teeth of the graz- ing kinds. The clawed {chalicotheres were present, though very little is known about them because of the fragmentary character of the remains. The Artiodactyla were much more varied and abundant, though they did not rival the great assemblage of these ani- mals found in the European Miocene. Of the peccaries little more can be said than that they were present in these faunas. The foreodonts were very numerous, both individually and generically ; two stages of the proboscis-bearing kind are found here together, the older, long-faced genus (+Promerycocherus) surviving from the Oligocene, while the newer Miocene type was short-faced and had a moderate proboscis (see Fig. 196, p. 373). Others had more the proportions of peccaries and still others were very small and presumably aquatic in habits. Camels abounded, both the grazing kinds which were ancestral to the modern forms of South America and Asia, and the great, browsing {giraffe-camels. The thornless deer and the antlered tdeer-antelopes were much like those of the Upper Miocene, slender and graceful little creatures, and there were also con- siderably larger ruminants ({Dromomeryzx) with straight, simple and non-deciduous horns, which may be called antelopes. The line of division between the lower Miocene and the uppermost Oligocene is a very obscure and difficult one to draw. Personally, I prefer to begin the Miocene with the widespread formation of the Great Plains, which has been variously named Arikaree, Harrison, Rosebud, etc., but this is a moot point. Concerning the lower part of these beds Osborn says: ‘‘They may be either: (1) Upper Oligocene or (2) transitional from Oligocene to Miocene, or (3) of pure 236 LAND MAMMALS IN THE WESTERN HEMISPHERE Fic, 127.— Gigantic tgiraffe-camel (tAlticamelus altus) from the middle Miocene of Colorado. Restored from specimens in the American Museum of Natural History. SUCCESSIVE MAMMALIAN FAUNAS 237 Lower Miocene age.” The upper division is referred to the Miocene without question by any one, but for the purposes of this rapid sketch it will be best to treat the two faunas to- gether. This many-named formation, for which the term Arikaree is here employed, as having priority, is found over extensive areas of South Dakota, northern Nebraska and 3 R-BRUCE HORiFA Pre | vit PP SYS I Fic. 128.— Most ancient American Antelope (tDromomeryx antilopina), middle Miocene. Restored from specimens in the Carnegie Museum and Princeton University. central Wyoming. The fauna was almost entirely a develop- ment from that of the North American Oligocene, with very little admixture of foreign elements, so that the land com- munication with the eastern hemisphere must have been difficult. In this, as in most of the Miocene formations, the smaller mammals are not fairly represented, and it is evident that much remains to be learned with regard to them; this is especially true of the upper division of this stage. The rodents, which were fairly numerous, were directly continuous with those of the upper Oligocene and included forms which were more or less distantly connected with the ' 238 LAND MAMMALS IN THE WESTERN HEMISPHERE modern hares, squirrels, beavers, sewellels, pocket-gophers and kangaroo-rats. A few Insectivora of doubtful reference have been found. Among the Carnivora there was also consider- able variety: dogs, large and small, were abundant, but all of them were decidedly primitive from the modern standpoint ; the cats were represented both by the true felines, which were probably immigrants, and by the fsabre-tooth series. There were several large and powerful mustelines, or members of the weasel family, which were likewise immigrants, one of which resembles in many ways the modern Wolverene (Gulo). Very interesting is the beginning of the raccoon family (Procyonide) or, at least, what is believed to be such, which arose from a branch of the dogs; this most ancient of the raccoons was ¢Phlaocyon, a small and slender animal. The earliest traces of the Proboscidea in America have been reported from this formation, but the fragmentary speci- mens are inconclusive. The Perissodactyla are among the commonest fossils. The rhinoceroses belonged to native stocks, including both the horned and hornless forms. The horned genus ({Diceratherium) differed from all other rhinoceroses in having a transverse pair of horns on the nose, and the species of the lower Miocene were quite small and light; the hornless genus (fCenopus) was a larger and heavier animal. Tapirs are rare as fossils and consequently not well known. While there were several kinds of horses, they all agreed in having short-crowned and relatively simple grinding teeth and three- toed feet ; they were smaller and of lighter, more slender build than those of the middle Miocene. The wonderful aberrant perissodactyls with clawed feet, the tchalicotheres (suborder +Ancylopoda), appear to have been more abundant in the Arikaree than at any other time in North America, though their history in this continent extends from the middle Eocene to the lower Pliocene. +tMoropus, the lower Miocene genus, was as grotesque a creature as could well be imagined and, in advance of experience, no one ever did imagine such a beast. SUCCESSIVE MAMMALIAN FAUNAS 239 With rather small and somewhat horse-like head, long neck, long fore limbs and shorter hind limbs, these extraordinary animals united short, three-toed feet, which were armed with enormous claws. The long persistence (to the Pleistocene of Asia) and wide geographical range of the tchalicotheres are sufficient evidence that their very unusual structure must Fic. 129.— The small, tpaired-horned rhinoceros (tDiceratherium cooki) of the lower Miocene. Restored from a skeleton in the Carnegie Museum, Pittsburgh. have been advantageous to them, but the problem of their habits and mode of life is still unsolved. From the character of the teeth, the long neck and fore limbs, it may, however, be inferred that they fed chiefly upon the leaves of trees. Even more numerous and varied were the Artiodactyla. Peccaries of a primitive sort were common, and we find the last of the series of {‘‘giant pigs,’’ which had been a very con- spicuous group throughout the Oligocene. The lower Miocene genus, tDinohyus, was a monstrous beast, six feet or more in height, with formidable canine tusks and a very long head made grotesque by bony excrescences upon the skull and jaws. For a pig, the legs were very long and the feet slender, having LAND MAMMALS IN THE WESTERN HEMISPHERE 240 aIBoUIeD oY} UI UOJIEYsS & WIZ po10j}soYy “qaings}}ig ‘umesnyy ‘QUDIOIT TOMOT OY} JO (snzDJa sndosopy4) s1ayZooYeYyoL YW — ‘OST ‘PIA = ie I Ge On vs Shs FNS SUCCESSIVE MAMMALIAN FAUNAS 241 but two toes. The foreodonts were present in great num- bers, both small and large forms; except for bodily stature and modifications of the head, they all looked very much alike ; {Merycocherus, with its incipient proboscis, here made its first appearance. The last representatives of a family ({Hyper- tragulide) of small and graceful artiodactyls are found in this formation. One of these ({Syndyoceras, see Fig. 215, p. 403), an animal considerably larger than the existing Musk-Deer, was in its way even more bizarre-looking than the tchalicotheres ; with an antelope-like head, it had four horns, one pair over the eyes, curving inward, and a shorter pair, with outward curvature, on the muzzle. Another genus (}Hypertragulus) was very much smaller and very slender. The camels were beginning to diversify and give rise to several phyla. One of the genera ({Protomeryx), which did not much exceed a sheep in size, probably represented the main stock, which led to the camels and llamas of to-day. A second ({Stenomylus) was a still smaller animal, with remarkably long and slender legs, and might be called a ‘“‘gazelle-camel,”’ while a third (tOxydactylus, see Fig. 209, p.392), which was larger and apparently the beginning of the tgiraffe-camels, was note- worthy for its long neck. All of these lower Miocene camels had deer-like hoofs, the characteristic pad or cushion which gives such an exceptional appearance to the feet of modern llamas and camels not being fully developed till a later period. A very important new element in the North American fauna was the appearance of the first deer ({Blastomeryx), which came in the latter part of the Arikaree stage and were the forerunners of a renewed immigration from the Old World, which had been broken off during the upper Oligocene. This, however, is a disputed point; Professor Osborn and Dr. Matthew believe that these animals were truly indigenous and derived from a long line of American ancestry. The same genus continued through the middle Miocene, as we have already seen, and therefore no further description of it is called for. R 242 LAND MAMMALS IN THE WESTERN HEMISPHERE The limits of the South American Miocene are very doubtful. The Parand formation, here regarded as lower Pliocene, may prove to be more properly referable to the upper Miocene. No other upper Miocene is known. To the earlier, probably middle, Miocene may be referred the wonderful Santa Cruz fauna of Patagonia. It is extremely Fig. 131.— The tgazelle-camel (tStenomylus hitchcocki) of the lower Miocene. Restored from skeletons in the Carnegie Museum, Pittsburgh. difficult to convey to the reader any adequate conception of this great assemblage of mammals, because most of them belonged to orders which have altogether vanished from the earth and are only remotely like the forms with which we are familiar in the northern hemisphere. To one who knows only these northern animals, it seems like entering another world when he begins the study of the Santa Cruz fossils. If any North American mammals had then entered South America, which is not probable, they had not extended their range as far as Patagonia. Marvellously rich and varied as the Santa 243 SUCCESSIVE MAMMALIAN FAUNAS “quOpoxo}| ‘snpyooruquér UoposaAT] “TT “Ux9zdOzT]| ‘wun107j01108 uopososyy} ‘OT “Te}dnsreur snoaoepeid ‘snowuobnjnd snufonphiyjorg| "6 ‘aleqyodeiyse| ‘wnubow wnisayodnysy| "8 ‘usezdozT]] ‘wnynosnuzw wnisayjooy]} “2 “Y,O[S-punoid} ‘sdaovuo) sdopdnyy| -g “yuopaydAB| ‘syv4ysnn snioydojdoyowjndorg| “Gg ‘ol[ipeutre ‘wnynjassay wmnr1ayjobag) “F “quapol ‘nyDADIXa DIpLDIO | “Eg *a1ay}OdA4| ‘azouysnDd wunuayjodhjo.g| ‘% ‘feldnsreur snoaoepaid ‘snyo.ysny syowsopnjp} *T ‘ayes ayy QAId 04 ‘a[ZuvJOeI OY} UTYIIM ‘Bop JequIod usepow v ‘sTeMUTEU ZNID BUY OY} Jo SezIs aATFeIBdUIOD oY} oyeI}SN]II 0} WBIdBIC — ‘ZET ‘DLT Satoh epee roles tT 5 Soy wun 244 LAND MAMMALS IN THE WESTERN HEMISPHERE Cruz fauna was, it did not contain everything that we should expect to find in it; several recent families of undoubtedly indigenous South American origin have left no ancestors in the early Miocene formations. For this, there are several obvious reasons. In part, these gaps in the history are merely due to the accidents of collecting and some of them will almost certainly be filled by future exploration. Other absentees will probably never be found, because the Santa Cruz beds are known only in the very far south, and the Miocene climate of the region, though much milder and more genial than the present one, must have been unsuitable for many tropical animals. Again, the Patagonia of that time appears to have been a country of open plains, with few trees, and hence ar- boreal forms were rare. While great numbers of large, flightless birds, some of them of enormous size, were entombed in the volcanic ash and dust which were spread over such wide areas and to such great depths, the extreme scarcity of reptiles is surprising; a few remains of lizards have been found, but no snakes, croc- odiles, or tortoises, and we have no information as to the plant-life of the region at that time. The mammals were al- most all of small or moderate size ; only one or two species were really large. One very striking and characteristic feature of the Santa Cruz fauna is the great abundance of marsupials which it contained and which resembled more or less those of modern Australia. There were no true Carnivora and their places were taken by a variety of carnivorous marsupials, some of which (e.g. tProthylacynus) were as large as wolves and were closely similar to the so-called Tasmanian Wolf (Thylacynus). Another genus ({Borhyena) had a short, bullet head, not un- like a small Puma in appearance and, besides, there were many smaller beasts of prey, in size like badgers and minks. Opos- sums were common and there were many very small herbivorous marsupials, which resembled, though perhaps but superficially, SUCCESSIVE MAMMALIAN FAUNAS 245 the Australian phalangers. At the present day South America contains no Insectivora, but in the Santa Cruz there was one family (fNecrolestide) of this order which bore considerable resemblance to the “golden moles” of South Africa. An extraordinary variety of rodents inhabited Patagonia in Santa Cruz times, all of them belonging to the Hystricomorpha, or porcupine suborder, and all referable to existing South Ameri- can families. There were none of the northern forms of ro- dents, neither rats, mice, squirrels, marmots, hares, nor rabbits, but a very numerous assembly of tree-porcupines, cavies, chinchillas, coypus and the like. The genera, though closely allied to existing ones, are all extinct, and the animals were very generally smaller than their modern descendants. A few small monkeys of unmistakably Neotropical type have been found, but like other arboreal and forest-living animals, they are very rare among the fossils. The Edentata were more abundant and diversified than at any other time in South American history of which the record is preserved. Two of the modern subdivisions of this order have not been certainly identified in the Santa Cruz collections, the arboreal sloths and the anteaters, and though they may be found there at any time, it will only be as stragglers from the warmer forested regions to the north, where these forms had doubtless long been present. Unfortunately, however, nothing is directly known concerning the life of those regions in Miocene times. On the other hand, three groups of edentates, two of them now extinct, were very copiously represented in the Santa Cruz formation, the armadillos, tglyptodonts and tground sloths. Of the many armadillos, some quite large, others very small, only a few can be regarded as directly ancestral to those now in existence; the truly ancestral forms were probably then living in the forests of Brazil and northern Argentina, in the same areas as the ancestral tree-sloths and anteaters. In comparison with the giants of the Pliocene and Pleistocene, the Santa Cruz tglyptodonts were all small, 246 LAND MAMMALS IN THE WESTERN HEMISPHERE the carapace rarely exceeding two feet in length, and, what it is particularly interesting to note, they departed much less widely from the armadillo type than did their gigantic suc- cessors. The tground-sloths were present in actually bewild- ering variety and they also were very small as compared with the huge animals of the Pleistocene, none of them exceeding the Black Bear in height or length, though proportionally much more massive, and many were no bigger than foxes. They had small heads, long bodies, heavy tails and short, thick legs; their teeth show that they were plant-feeders, but their feet were armed with long, sharp and formidable claws. Among this great host of Santa Cruz tground-sloths may readily be noted the probable ancestors of the gigantic creatures which were such characteristic elements of the Pliocene and Pleistocene faunas. There was an extraordinarily rich and varied assemblage of hoofed animals, all utterly different from those of the northern hemisphere and belonging to groups which have never been found outside of South and Central America. Of these groups there were five, which by different writers are variously re- garded as orders or suborders, a matter of very secondary im- portance. Individually, the commonest of the hoofed mam- mals were the tToxodonta, which ranged in size from a sheep to a tapir, heavily built and clumsy creatures, with absurdly small, three-toed feet ; in some of the species there was a smal} median horn on the forehead. As with the tglyptodonts and tground-sloths, the contrast in size between the Santa Cruz ancestors andthe Pleistocene descendants was very striking. A very numerous and varied group was that of the {Typotheria, all small animals, some no larger than rabbits, others the size of small foxes. It requires a decided effort to think of these ttypotheres as being really hoofed animals at all, as their whole appearance must have been much more like that of rodents, yet their structure clearly demonstrates their near relationship to the ttoxodonts. Still a third group of the same SUCCESSIVE MAMMALIAN FAUNAS 247 series, the tEntelonychia, is of great interest, for, as in the tchalicotheres of the northern hemisphere, the hoofs had been transformed into claws and their five-toed feet had a truly grotesque appearance, not diminished by the long and power- ful limbs and relatively small head. This is the third example of that paradoxical creature, a ‘“‘hoofed animal” with claws instead of hoofs, and in each of the three instances, there is every reason to believe, the trans- formation proceeded independently. Among the _perisso- dactyls the jfchalicotheres (p. 238) underwent this change; in North America the tAgriocheeride, a family of artiodactyls, had a very similar history, while in South America the tEntel- onychia arose from the same stock as the ftoxodonts, with which they were nearly allied. They were among the largest animals of Santa Cruz times and ranged in size from an ox to a rhinoceros. There was a fourth group, the tAstrapotheria, concerning which our knowledge is tantalizingly incomplete, some species of which were the largest of known Santa Cruz mammals, while others were much smaller. They had short, domed heads, with a considerable proboscis, and were armed with formidable tusks, which were the enlarged canine teeth, the only known instance of large canine tusks among the indigenous South American hoofed animals. The limbs were long and not very massive, the feet short, five-toed and somewhat elephantine in appearance. These bizarre animals would seem to have held a rather isolated position among the South American ungulates, and though they may be traced back to the most ancient mammal-bearing beds of that continent, their relation- ships are still obscure; much more complete material must be obtained before this problem can be definitely solved. Both the ftAstrapotheria and the +Entelonychia died out shortly after the end of the Santa Cruz. From many points of view the most interesting members of the Santa Cruz fauna were the {Litopterna, an order which also 248 LAND MAMMALS IN THE WESTERN HEMISPHERE went back to the earliest South American Tertiary. In the Miocene and Pliocene the order was represented by two very distinct families, the -Macrauchenide and {Proterotheriide, which were superficially very unlike. In the Santa Cruz beds is found a genus (f7'heosodon) which was apparently the di- rect ancestor of the Pampean tMacrauchenia. The Miocene genus was a much smaller animal and had hardly more than an incipient proboscis, but otherwise was very like its Pam- pean successor; it was somewhat larger and heavier than a Llama and probably bore some resemblance to that animal in appearance. The long, narrow head, with its prehensile upper lip, must have had an almost reptilian likeness from the numerous uniform and sharp-pointed teeth with which the front of the jaws was supplied ; the neck was elongate, the body short and rather slender and the legs long, ending in three nearly equal toes. The fproterotheres, on the other hand, were almost the only Santa Cruz ungulates which had nothing outré or grotesque about them to the eye of one habituated to the faunas of the northern hemisphere. They were small, graceful animals, very like the Miocene horses of the north in their proportions, though having much shorter necks and shorter, heavier heads. In some genera of this family (e.g. Diadiaphorus, tProtero- therium) the feet were three-toed and most surprisingly horse- like in shape, but one genus ({tThoatherium) was absolutely single-toed, more completely monodactyl than any horse. The horse-likenesses ran all through the skeleton and are so numerous and so striking that several writers have not hesitated to incorporate the {Litopterna with the Perissodactyla, but this I believe to be an.error. If the tproterotheres were not perissodactyls, as I am convinced they were not, they afford one of the most remarkable examples of convergent evolution among mammals yet made known. SUCCESSIVE MAMMALIAN FAUNAS 249 3. Oligocene North America.— The John Day formation of eastern Oregon represents the upper Oligocene and has yielded a very extensive series of mammals, though with some obvious gaps that remain to be filled by future work. The land-connection with the Old World which had existed in the lower Oligocene and was restored in the lower, or at latest in the middle, Miocene, was interrupted in John Day times, and so the mammals assumed a purely indigenous character. No opossums or other marsupials have been found, and nothing is known of the Insectivora. Of the Carnivora, there were but three families, and one of these, the mustelines, was represented but scantily by a few small species. Cats of the tsabre-tooth subfamily were common and one species was quite large, almost equalling the Jaguar in length ; but most of the species were small, much smaller than the Pleistocene members of the group. True cats are not definitely known to have been present, but there were two genera ({Nimravus and tArchelurus) which have been called the ‘‘false tsabre- tooths,” which may prove to be referable to that series. The dogs, on the other hand, were remarkably numerous and diversified, more so than ever before or since; none of them was very large, the largest but little exceeding the Timber Wolf in size, and some were extremely small; but the number of distinct genera and species and the differences among them are quite remarkable. Both long and short-faced forms and early stages of the {‘‘bear-dogs,” and }‘‘hyena-dogs,”’ and ancestral forms of the wolves and dholes may be distin- guished, a truly wonderful assemblage. The rodents also were numerous and varied, including ancient and extinct genera of the beavers, squirrels, mice, pocket-gophers and hares and the earliest distinguishable ancestors of the sewellels (Aplodontiide). The remainder of the known John Day fauna was composed 250 LAND MAMMALS IN THE WESTERN HEMISPHERE of artiodactyls and perissodactyls. The latter had suffered serious losses as compared with the preceding or White River stage. Up to and through White River times the perisso- dactyls had held their own in actual diversity, though the rise of the artiodactyls had put an end to the dominant position which they had maintained in the Eocene. With the John Day the actual decline may be said to have begun. The rhinoceroses were represented chiefly by the tdiceratheres, with a transverse pair of horns, some species of which were much larger than those of the lower Miocene. Hornless rhinoceroses have not yet been certainly found, though there is every rea- son to believe that they then existed, as they unquestionably did both before and after. Tapirs occurred but rarely and the horses were individually abundant, though in no great diversity ; they were smaller and lighter than the horses of the lower Miocene. Enough has been found to demonstrate the presence of the clawed tchalicotheres, but not to show how they differed from their immediate successors. In the number of individuals, species, genera and families, the artiodactyls of the John Day much exceeded the perisso- dactyls. The peccaries were numerous, but smaller and more primitive than those of the succeeding age, as were also the tgiant pigs, or tentelodonts, but the latter were very large. The peculiarly North American family of the toreodonts was very numerously represented, and one genus ({Promeryco- cherus), comprising animals not unlike the Wild Boar in size and shape, was the probable beginning of the series of proboscis- bearing foreodonts, which led to such grotesque forms in the middle and upper Miocene. A family closely allied to the toreodonts, and by many writers included in the latter, is the very remarkable group of the tAgriochceride, which was dis- tinguished by the long, stout and cat-like tail and by the possession of claws instead of hoofs. The family is not known to have existed later than the John Day and no trace of it has been found in the succeeding formations. The camels SUCCESSIVE MAMMALIAN FAUNAS 251 seem to be all comprised in a single genus ({Protomeryx) which was the same as that found in the lower Miocene. A very small and dainty little creature (tHypertragulus) belonged to another family, the relationships of which are not clear. To the middle and lower Oligocene is referred the great White River formation of South Dakota, Nebraska,Wyoming, etc., which is divisible into three clearly marked substages. The White River contains the best-known fauna of all of the North American Tertiaries, for collecting in these beds has been carried on for more than sixty years, and a greater number of complete and nearly complete skeletons has been secured than from any of the other formations. It is plainly evident that a land-connection existed with the Old World, which was interrupted in the John Day, as is shown by the intermigration of characteristic forms ; but some barrier, presumably climatic, prevented any complete interchange of mammals, and very many genera and even families remained confined to one con- tinent or the other. The aspect of the White River fauna changes in accordance with the direction from which it is approached. If one comes to the study of it from the Eocene, it displays a very modern aspect, given by the almost complete disappearance of the archaic groups of mammals and by the great multiplication of genera and species belonging to the progressive orders. These genera, it is true, are all extinct, but many of them stood in an ancestral relationship to modern forms. On the other hand, if approached from the Miocene side, the White River mammals seem to be very ancient and primitive and very different from anything that now lives. We speak of horses and rhinoceroses, dogs and cats, in this fauna, but those terms can be employed only in a very wide and elastic sense to desig- nate animals more or less distantly allied to those of the present day. Several species of opossums, some of them very small, were the only marsupials in North America then, as they are now. Fie. 1383.—1. tArcheotherium. 2. Ancestral camel (tPoébrotherium). 3. tMerycoido- don. 4. tAgriocherus. 5. Ancestral horse (tMesohippus). 6. tHoplophoneus. 7. tBothriodon. 8. tHyenodon. 9. tCursorial rhinoceros (tHyracodon). 10. tPro- toceras. 11. Hornless rhinoceros (tCenopus). (252) SUCCESSIVE MAMMALIAN FAUNAS 253 There was quite a variety of Insectivora; some were survivals of a family that was abundant in the Eocene, others, like the hedgehogs, moles and shrews, were probably immigrants. Here we find the last of a group (order or suborder) of ancient and primitive flesh-eaters, the tCreodonta, that had played a great réle in the Eocene and Paleocene of North America and NN Fic. 134. — White River ttitanothere (tTitanotherium robustum) reduced to the same scale as Fig. 133. Europe. In White River times but a single family ({Hyzno- dontide), with two genera, remained of the Eocene host. One _ of these genera (tHemipsalodon), a very large beast of prey, which was almost identical with the Old World genus {Pterodon, was confined to the lower substage of the White River beds in the Northwest Territory of Canada; the other, tHyenodon, which was also an Old World form, was represented abundantly in the United States by many species. In size, these species ranged from a small fox to a large wolf, but they all had dis- proportionately large heads, and small, weak feet, with blunt claws, so that they must have been very curious-looking creatures and were probably carrion-feeders rather than active catchers of prey. The White River members of the family 254 LAND MAMMALS IN THE WESTERN HEMISPHERE were migrants from the eastern hemisphere, for, though small’ and primitive representatives of it occurred in the North American Eocene, as well as in the corresponding formations of Europe, the family appears to have died out in America and to have been renewed by the Oligocene migration. Coincident with this decline of the tereodonts and, no doubt, causally connected with it, was the rise of the true Carnivora, which for the first time were numerous and were divisible into three distinct families. Small and primitive representatives of the wolves ({Daphenus) and possibly also of the foxes (tCynodictis) were quite common, and there were a few species of the musteline family, evidently immigrants and the most ancient yet found in America. There were several species of the tsabre-tooth cats (tDinictis and tHoplophoneus) all of which, except in the uppermost substage, were quite small, few of them exceeding the Canada Lynx in size. A much larger animal ({Husmilus, also European) appeared in the latter part of the stage. None of the true cats, or feline sub- family, has been obtained. Nothing is yet known of the time and place of origin of the jsabre-tooth series, for they ap- peared at approximately the same date in Europe and America, and in neither continent have any possible ancestors been found in preceding formations. The problem is like that of the Proboscidea (see p. 2384), but Egypt has given no help in the case of the tsabre-tooths, and, by a process of elimination, we reach the conclusion that these strange creatures probably arose somewhere in Asia and sent out migrants eastward and westward. The Rodentia were fairly abundant and present a strange mixture of ancient and comparatively modern types. One very common genus ({Ischyromys), which was the last rem- nant of a family almost limited to the North American Eocene, was associated with the earliest American mice, arboreal and ground squirrels, beavers and rabbits; some, if not all, of these were immigrants. SUCCESSIVE MAMMALIAN FAUNAS 255 The hoofed mammals were present in fairly bewildering variety, but were restricted to the two orders of the Perisso- dactyla and Artiodactyla. The Perissodactyla, while they no longer had the relatively dominant position which they held in the middle Eocene (see p. 270), had suffered no actual loss; and no less than seven families of them, or six by another scheme of classification, had members in the North America of White River times, a very notable difference from the present order of things, when there are but three families in the entire world, none of which enters North America. The Eocene family of the {titanotheres became extinct at the end of the lower substage of the White River, but in that substage there was a marvellous abundance of these huge beasts, some of which were of almost elephantine stature and bulk. The pair of great bony, horn-like protuberances on the nose varied much in size and form in the different species, short to very long, triangular, cylindrical, flattened and shovel-shaped, and gave these ungainly creatures somewhat the appearance of strange and very large rhinoceroses. The ftitanotheres were a typically North American family, but sent migrants to the Old World, at least two species reaching southeastern Europe. Rhinoceroses too were extremely numerous and diversified throughout the stage and are very plainly divisible into three strongly contrasted series, which are sometimes regarded as three subdivisions of the same family and some- times put into two separate families. One of these series, the thyracodonts (tHyracodon), was composed of small, long- necked and long-legged, slender and lightly built, cursorial animals, but with short, heavy heads, which gave them a somewhat clumsy look; having neither horns nor tusks, they were entirely defenceless and depended for their safety upon speed alone. The second series, or tamynodonts ({Met- amynodon), formed the very antithesis of the first, — large, heavy, short-necked, and short-legged and probably amphibi- ous in manner of life, they were armed with formidable 256 LAND MAMMALS IN THE WESTERN HEMISPHERE tusks; and their skulls were so curiously modified as to bear a distinct resemblance to the skull of a huge carnivore. The tamynodonts migrated to the Old World and occur in the Oligocene of France, but the thyracodonts would seem never to have left North America. The third series, that of the true rhinoceroses, comprised several genera at different levels in Fic. 135. —+tHornless rhinoceros (tCenopus tridactylus) of the White River stage. Restored from a skeleton in the American Museum. the White River beds ({Trigonias, tCenopus, etc.) ; they were of uncertain origin and it has not yet been determined whether they were immigrants or of native stock. Many species have been found, varying much in size, up to that of a modern tapir, and not unlike one in proportions, for they were of lighter build and had relatively longer legs than any existing rhinoceros. The species of the lower and middle substages were all horn- less, but in the uppermost substage we find skulls with a pair of nasal horns in an incipient stage of development. This was the beginning of the tpaired-horned rhinoceroses ({Diceratherium) which so flourished in the John Day and the lower Miocene. SUCCESSIVE MAMMALIAN FAUNAS 257 Of the horses there was no great variety and all the species so far discovered are included in a single genus (+Mesohippus), though there was a decided increment in the size of the suc- cessive species from the earlier to the later portion of the stage. Looked at superficially, it seems absurd to call these little creatures ‘‘horses’’ at all and the term can be justified only as implying that they were ancestral members of the family. The largest of the White River species hardly exceeded a sheep in size and all of them had comparatively short necks, long and slender legs and three-toed feet. The low-crowned grind: ing teeth show that they were browsers, not grazers. . The abundant Eocene family of the tLophiodontide made its last appearance in the White River, where it was scantily repre- sented by slender, long-legged animals ({Colodon), with feet singularly like those of the contemporary horses, except that there were four toes in the front foot. Tapirs ({Protapirus) were very much less common than rhinoceroses or horges and were hardly half as large as the existing species of the family and of relatively far more slender form; the development of the proboscis had already begun. Lastly, the presence of the clawed fchalicotheres has been reported from the lower Oligocene of. Canada, but the material is too fragmentary for generic reference. Though the number of artiodactyl families yet identified among the White River fossils is no larger than that of the perissodactyl families, the artiodactyls greatly preponderated in individual abundance. The peccaries, which were fairly common, resembled those of the John Day, but were consider- ably smaller. Of the camels, there were two series, one of which ({tHotylopus), lately described by Dr. Matthew, is of yet unknown significance, while the other (tPoébrotherium) was apparently the ancestor common to all the subsequent phyla of camels and Ilamas. This extremely interesting genus had species which ranged in size from a gazelle to a sheep, had two toes in each foot, a moderately elongate neck and teeth which Ss 258 LAND MAMMALS IN THE WESTERN HEMISPHERE were beginning to assume the high-crowned character. From this it may be inferred that those animals were, partly at least, of grazing habit, which was rare among White River ungulates, most of which fed upon leaves and soft and succulent plants. An extinct family, the tHypertragulide, were a greatly diver- sified group of dainty little creatures, one of which (tHypisodus) was no larger than a rabbit and had high-crowned teeth. The other genera ({Leptomeryx, tHypertragulus) must have resembled in form and proportions the tiny little chevrotains or “‘mouse-deer”’ of the East Indian islands. Late in the age arose a larger form of this family, nearly equalling the Musk-Deer in size, the extraordinary genus {Protoceras, which was, especially the males, a grotesque object. The males had a pair of upper canine tusks and two pairs of prominent long protuberances on the skull. This, or some similar form, must have been the ancestor of the still more bizarre {Syndyoceras of the lower Miocene. The foreodonts were by far the commonest of White River mammals, and evidently they roamed the woods and plains in great herds. There were several species, larger and smaller, of the abundant genus ({Merycoidodon) but the largest did not surpass a modern peccary in size and was somewhat like that animal in appearance, but had a shorter head and much longer tail. In the upper substage appeared a very peculiar genus of this family (}Leptauchenia), animals with short, deep, almost monkey-like heads, and presumably aquatic in habits. The tagriocherids were very much less common; they may be described roughly as toreodonts with very long, cat-like tails and clawed feet. All of the foregoing artiodactyl families were exclusively North American in Oligocene distribution; even the camels did not reach Asia till the Pliocene, and the other families never invaded the Old World at all. There were, however, two additional families, which also occurred in the eastern hemisphere, whence one of them, and possibly the other, was SUCCESSIVE MAMMALIAN FAUNAS 259 derived. The unquestionably Old World family, that of the tanthracotheres, was represented in the White River by two genera ({Bothriodon and tAnthracotherium), which were short- legged, long-snouted, swine-like animals, which have no near relations in the modern world. The other family, the tgiant cd Fie. 136. — tMerycoidodon culbertsoni, the most abundant of White River toreodonts. Restored from a skeleton in the American Museum of Natural History. pigs, which we have already met with in the lower Miocene and upper Oligocene, is of doubtful origin, and nothing has yet been found in the preceding formations of either North America or Europe which can be regarded as ancestral to them. The White River genus (tArchewotherium) was very like the John Day and Arikaree genera, but most of the species were much smaller and some were not so large as a domestic pig. In the uppermost beds, however, are found huge species, which rivalled those of the subsequent formations. That these strange animals were rooters and diggers and therefore pig-like in habits is indicated by the manner in which the teeth are worn. IN THE WESTERN HEMISPHERE LAND MAMMALS 260 ay} UI UOJa]aYS & UOJ pa104soy ‘APISIOATU—) UOZODULIG JO uMosnuUt ‘IBVYS IBA OFM IOMOT OY} WIOIF (Suabur wnisayjomyoLp 4) Bid yuVry| — ‘LEST “OlLT SUCCESSIVE MAMMALIAN FAUNAS 261 South America. — The older continental Tertiary forma- tions of South America cannot be correlated with those of North America or Europe, because they have nothing in common. Difficult as it is to give a correct and adequate conception of the Tertiary mammalian life of the northern hemisphere to one who has not made a study of it, it is far more difficult in the case of South America. The stock of adjectives, such as “peculiar,” “bizarre,” ‘grotesque’ and the like, already overworked in dealing with northern forms, is quite hopelessly inadequate where everything is strange. In addition to this, we are seriously handicapped in treating of the Oligocene and Eocene of South America by very incomplete knowledge. Many fossils have been collected and named, but the great majority of these are known only from teeth; a few skulls and limb-bones have been described, but no skeletons, and therefore much is very uncertain regarding these faunas. The Deseado formation (Pyrotherium Beds) has been variously referred by different writers from the upper Creta- ceous to the lower Miocene, but its most probable correlation is with the Oligocene. Though most of the mammalian groups are the same as those of the Santa Cruz, the proportions of the various orders in the two faunas are very different, but, to some extent, the difference is probably illusory and due to the conditions of fossilization, for, as a rule, the small mammals are much less frequent and well preserved in the older beds. As in the Santa Cruz, the marsupials were the only predaceous mammals, and some of them attained gigantic size; but no such variety of these beasts of prey has been found in these beds as occurred in the middle Miocene. In addition, there were numerous small herbivorous marsupials. One of the most striking differences from the Santa Cruz fauna was in the very much smaller number of Edentata, which, instead of being extremely common, are quite rare among the fossils. No doubt there was a real and substantial difference in this respect, but it was probably not so great as it seems, and the 262 LAND MAMMALS IN THE WESTERN HEMISPHERE same three suborders are found in both formations. One of the few tground-sloths that have been obtained was very large ({Octodontheriwm crassidens), a much larger animal than any species of the suborder that is known from the Santa Cruz. The jglyptodonts were also rare, and only two genera and species have been described from very scanty remains. Arma- dillos, on the other hand, were much more common, and no less than eleven genera have been named, three of which occurred also in the Santa Cruz. Among these was the remarkable genus {Peltephilus, in which the anterior two pairs of plates of the head shield were modified into horn-like spines. Equally striking was the remarkable diminution of the Rodentia, as compared with those of the Santa Cruz, though, of course, this is an inaccurate mode of stating the truth, occasioned by the fact that we are following the history in reverse order. It would be preferable to say that the rodents underwent a remarkable expansion in the Santa Cruz. These rodents of the Deseado stage are the most ancient yet dis- covered in South America and represent only two families, both belonging to the Hystricomorpha, or porcupine group. If, as Dr. Schlosser and other European paleontologists main- tain, the Hystricomorpha were all derived from a family of the European Eocene, this would necessitate a land-connection between South America and the Old World independent of North America, for the latter continent had no hystricomorph rodents until the connection between the two Americas was established. The great bulk of the Deseado fauna is made up, so far as individual abundance is concerned, of hoofed animals belong- ing to the typically South American groups. The tToxodonta were represented partly by genera which were the direct ancestors of the common Santa Cruz genera ({Pronesodon, +Proadinotherium), and, more numerously, by a very peculiar family, the tNotohippide, which had highly complex, cement- covered grinding teeth. Still a third family of this suborder, SUCCESSIVE MAMMALIAN FAUNAS 263 the {Leontiniide, was highly characteristic of the Deseado fauna and is not known from the Santa Cruz. These were large animals, with a small horn on the tip of the nose and low- crowned, comparatively simple grinding teeth. Even more abundant were the {Typotheria, small forms which were Fic. 138. — Horned ftoxodont ({Leontinia gaudryi), Deseado stage. Restored from a skull in the Ameghino collection. ancestral to the Santa Cruz genera, larger ones which died out without leaving successors and one quite large animal ({Zu- trachytherus) which seems to have been the ancestor of the Pliocene and Pleistocene +Typotherium. This series is not known to have been represented in the Santa Cruz and may have withdrawn from Patagonia at the end of the Deseado stage. The {Entelonychia, those strange toxodont-like animals with claws instead of hoofs, were much more numerous and varied than they were afterward in the Santa Cruz, when they 264 LAND MAMMALS IN THE WESTERN HEMISPHERE were on the verge of extinction, and included both very small and very large species. The {Pyrotheria, a suborder which is not met with in the Santa Cruz or later formations, likewise included some very large forms. The typical genus, tPyro- therium, included large, relatively short-legged and very mas- sive animals; the upper incisors formed two pairs of short, downwardly directed tusks, and in the lower jaw was a single pair of horizontally directed tusks; the grinding teeth were low-crowned and had each two simple, transverse crests. These grinding teeth and the lower tusks so resemble those of the ancestral Proboscidea in the Oligocene of Egypt, that the tpyrotheres have actually been regarded as the beginnings of the tmastodons and elephants, but this is undoubtedly an error. The tAstrapotheria, another group which became ex- tinct at or soon after the end of the Santa Cruz, were rel- atively abundant in the Deseado and counted some very large species. Finally, the }Litopterna were represented by the same two families as continued through the Pliocene and one of them far into the Pleistocene. The horse-like tproterotheres were present, but not enough of them has been obtained to show whether or not they were in a notably less advanced stage of development than those of the Santa Cruz. The tmacrauchenids were quite similar to those of the latter for- mation, though considerably smaller. In addition, there were a few genera, survivals from earlier times, which were not referable to either of these families. The large number of genera, especially among the {toxo- donts and ftypotheres, which had high-crowned, cement- covered teeth, may be taken as an indication that grazing habits had already begun to be prevalent. Of this wonderful assemblage of hoofed animals, divisible into six separate groups, whether of ordinal or subordinal rank, not a trace remains to-day. Not only are all the species, genera and families extinct, but the suborders and orders also. Further, this was a very strictly autochthonous fauna, so far SUCCESSIVE MAMMALIAN FAUNAS 265 as the hoofed animals were concerned, and no member of any of the six groups has ever been found outside of the Neotropical region. 4, Eocene North America. — In the western interior of North America the Oligocene followed so gradually upon the Eocene, that there is great difficulty in demarcating them and much difference of opinion and practice obtains as to where the boundary line should be drawn. Not to depart too widely from the scheme . used by Professor Osborn, the Uinta stage is here treated as uppermost Eocene, though this is a debatable procedure. For several reasons, the extraordinarily interesting and sig- nificant Uinta fauna is far less completely known than that of the preceding Bridger and succeeding White River stages. For one thing, it has been much less thoroughly explored, and it may be confidently expected that future exploration will greatly enlarge our knowledge. The smaller mammals of the Uinta are particularly ill- known. No Insectivora have yet been found, though this gap will assuredly be filled; rodents are scanty in the collec-_ tions and include only two families, one the fischyromyids, which were still common in the White River, the other of doubtful position, but not improbably to be considered as the beginning of the pocket-gophers (Geomyide#). The archaic flesh-eaters, or tCreodonta, were represented by two fami- lies, one comprising smaller animals with somewhat cat-like, shearing teeth (fOxyenide), the other, very large beasts with crushing teeth (tMesonychide), neither of which con- tinued into the White River. As compared with the middle and lower Eocene, the tcreodonts had greatly diminished and, to replace them, the true Carnivora were beginning to come in. As yet, however, only small and very primitive dog-like forms are known and no trace of tsabre-tooths or mustelines has been found. Indeed, it is very doubtful whether mem- bers of these families ever will be found in the Uinta, for their 266 LAND MAMMALS IN THE WESTERN HEMISPHERE presence in the succeeding White River was probably due to immigration. The Perissodactyla were the preponderant type of hoofed animals, and ancestral forms of most of the White River genera have already been identified. The ftitanotheres ({Diplacodon, {Protitanotheritum) were much smaller and lighter than those of the lower White River and had much shorter horns. The thyracodonts, the lightly built, cursorial rhinoceroses, were represented by a genus ({tTriplopus) which was smaller and more slender than the White River form (tHyracodon) and its teeth were of distinctly more primitive character. The heavy, massive and presumably aquatic tamynodonts (tAmyn- odon). were likewise smaller and less specialized than their descendants of the Oligocene. No member of the true rhinoc- eros series has yet been identified in the Uinta, but there is some reason to think that they were nevertheless present. Tapirs are distinctly indicated by certain fossils, but they are still too incompletely known to make possible any statement as to their degree of development. The horses (tEpihippus), like the other families mentioned, were much smaller and dis- tinctly more primitive than their successors in the Oligocene. The Artiodactyla were, for the first time in the history of North America, as numerous and as varied as the perisso- dactyls and, with the exception of the peccaries and tanthra- cotheres, representatives of all the White River families are known. The finding of the peccaries is merely a question of further exploration, but the fanthracotheres were migrants from the Old World, and there is no likelihood that they will be discovered in the Uinta at any future time. Fairly large, pig-like animals, probably referable to the tgiant-pigs or fen- telodonts, occurred, but nothing has yet been found which can be considered as the direct ancestor of the White River genus. As was true of the perissodactyls, the Uinta artiodactyls were nearly all much smaller and more primitive than their Oligocene descendants and the differences are most interesting from the SUCCESSIVE MAMMALIAN FAUNAS 267 evolutionary point of view. The ancestral camel ({Protylopus) was a little creature no bigger than a fox-terrier, though the thypertragulids ({Leptotragulus) were as large as |Leptomeryx and tHypertragulus of the White River. The most ancient known members of the toreodonts (}Protoreodon) and the tagriocherids ({Protagriocherus) are found in the Uinta. The middle Eocene fauna, Bridger stage, though it passed upward very gradually into that of the Uinta, was yet, on the whole, very different from the latter. It was exclusively indig- enous and so radically distinct from the mammals of corre- sponding date in Europe as to preclude the possibility of a land- bridge with that continent. In the lower Eocene, as will be shown in a subsequent page, the communication between the two continents was broadly open and the faunas of the two continents were much more closely similar than they have ever been since. It is really remarkable to see with what com- parative rapidity the two regions, when severed, developed different mammals under the operation of divergent evolution. . Had the separation continued throughout the Tertiary and Quaternary periods, North America would now have been as peculiar zodlogically as South America is, a result which has been prevented by the repeated renewal of the connection. The characteristic features of the Bridger mammalian fauna were chiefly due to the great expansion and diversification of certain families, which began their career at an earlier stage, and to the disappearance of many archaic groups which had marked the more ancient faunas. Other archaic groups, however, survived and even flourished in the Bridger, and of these it is particularly difficult to convey a correct notion to the reader, because they were so utterly unlike anything that now lives. One of these orders, the +Tzniodontia, which had so many points of resemblance to the fground-sloths that several writers have not hesitated to include them in the Edentata, survived only into the older Bridger, but the equally problematical }Tillodontia then reached their culmination, 268 LAND MAMMALS IN THE WESTERN HEMISPHERE though they were not very numerous. Though not at all related to that group, the {tillodonts looked like huge rodents, with their chisel-like incisor teeth. There was a remarkable assemblage of Insectivora, more numerous and varied than in any subsequent formation, no less than six families being known. One of these somewhat doubtfully represented the moles and two others modern Asiatic groups. The very unexpected discovery of an armadillo in the Bridger has been reported, but the propriety of referring this animal to the armadillos, or even to the edentates, has not yet been proved, and it would therefore be premature to discuss its significance. The only marsupials were opossums. So far as our information extends, there were no true Car- nivora in the Bridger, all the beasts of prey of the time belonging to the archaic {Creodonta, which then reached their maximum development in numbers and diversity. One family (tOxy- eenidz) included large and powerful flesh-eaters, with cat-like . dentition and short, rounded, lion-like heads, long bodies and tails and short, heavy limbs, giving them the proportions of otters. Another (the tHyznodontide) comprised small, long-headed, fox-like and weasel-like animals, which doubtless preyed upon small mammals and birds. A third family (tMesonychide) was made up of moderate-sized, long-jawed creatures, which must have resembled, rather remotely, short- legged and long-tailed wolves and hyenas. Their habits and mode of life are somewhat problematical, for their grinding teeth were blunt, not adapted to the shearing of flesh, and their claws were broad, almost hoof-like. Such creatures could hardly have subsisted by the pursuit of living prey and were probably carrion-feeders and more or less omnivorous. The {Miacide, a family which connected the fcreodonts and true carnivores and might almost. equally well be placed in either group, were externally much like the small thysenodonts, but were more efficiently equipped for the capture and devouring of prey. SUCCESSIVE MAMMALIAN FAUNAS 269 Of the archaic and extinct orders of hoofed animals, the only one which persisted from earlier times into the Bridger and greatly flourished there was the tAmblypoda, one family of which (fUintatheriide) was preéminently characteristic of middle Eocene life, becoming very rare and then dying out in the upper Eocene. The jfuintatheres of the Bridger under- went considerable modification in size and appearance within ee ee Fic. 139. — A mesonychid tereodont ({Dromocyon velor) of the Bridger stage. Restored from a skeleton in the Museum of Yale University. the limits of the stage, the larger and stranger species appearing toward the end of the time. Most of these great creatures may fairly be called gigantic, for they equalled the largest modern rhinoceroses and smaller elephants in size. The body, limbs and feet were so elephantine in character that they were once believed to be ancestral Proboscidea, but the teeth and the fantastic skull were so radically different that this belief was long ago abandoned. The upper canine teeth were converted, in the males, into formidable spear-like or scimitar- like tusks, protected by great flange-shaped expansions of the 270 LAND MAMMALS IN THE WESTERN HEMISPHERE lower jaw; bony knobs on the end of the nose probably sup- ported a pair of dermal horns like those of a rhinoceros and, in addition, a pair of high, cylindrical, horn-like, bony pro- tuberances arose above the eyes and another, more massive pair, near the back of the head. It would be difficult to imagine more extraordinary creatures than the fuintatheres, which were the largest land-mammals of their time. The family was entirely confined to North America, no trace of them having been found in any other continent. While the backward and archaic orders, most of which have left no descendants in the modern world, had thus a stately representation in Bridger times, they were outnumbered in genera, species and individuals by the progressive orders, which are still in more or less flourishing existence. The Primates, whether lemurs or monkeys, were numerous, and this, so far as is definitely known, was their last appearance in extra-tropical North America. They may at any time be found in the Uinta, but there is small probability that they will ever turn up in the White River or later formations. The many rodents all belonged to the tischyromyids, an extinct family which, there is much reason to believe, was ancestral to many families of the squirrel-like suborder of Sciuromorpha. Most of them were species of a single genus (fParamys) and varied in size from a mouse to a beaver, or even larger. The Perissodactyla may be said, in one sense, to have reached their culmination in the Bridger; not that many of them, such as the horses and rhinoceroses, did not advance far beyond their state of development in the Eocene, but at no subsequent time did the order as a whole possess such domi- nating importance. There were five or six families of peris- sodactyls in the Bridger, and their remains are much the most abundant fossils found there. Individually, the commonest perissodactyls of the time were the {titanotheres, of which there were several genera and many species, differing chiefly in size and proportions, though the largest hardly exceeded SUCCESSIVE MAMMALIAN FAUNAS 271 Fig. 140.— Some characteristic mammals of the Bridger Eocene reduced to a uniform scale, with « pointer dog, in frame, for comparison. 1. Primitive rhinoceros (tHyrachyus eximius). 2.+Tritemnodon agilis. 3. tPatriofelis ferox, and 4, tDro- mocyon velox, tcreodonts. 5. Primitive rodent ({Paramys delicatior). 6. tUintathe- rium alticeps. 7. fTitanothere (tMesatirhinus superior). a modern tapir in stature and was not dissimilar in appearance. These Bridger {titanotheres were considerably smaller than those of the Uinta and therefore very much more so than the White River forms; it was not till the latter stage that the family lived up to its name of “titanic beasts.” By far the 272 LAND MAMMALS IN THE WESTERN HEMISPHERE commonest of the genera in the middle and lower Bridger was +Paleosyops, which was hornless, while in the upper part of the beds are found genera (e.g. |Manteoceras and {Dolicho- rhinus) in which the horns were just beginning to appear. Another extinct family, the tLophiodontide, which was very abundant in the European Eocene, formed a very subordinate - element in: this fauna and included a number of small tapiroid genera (e.g. tHelaletes). The horses ({Orohippus) were very small and primitive creatures, no bigger than a fox, with four toes in the front foot and three in the hind. So completely different in appearance and proportions were these little animals from any of the modern horses, that it requires an effort of the imagination to think of them as belonging to the same family, and it is only by employing the family to designate a genetic series that such a classification can be justified. The thyracodonts, or cursorial rhinoceroses, were very abundantly represented by a number of small and medium-sized animals (tHyrachyus) which had less specialized teeth, shorter neck and limbs than their upper Eocene and Oligocene successors, and four toes in the front foot; one genus (tColonoceras) had a pair of nasal horns, but would seem to have died out without leaving descendants. In the upper part of the beds is found the Uinta genus. {T'riplo- pus, with three-toed fore foot ; and in the same division occurs another Uinta genus, tAmynodon, the most ancient known species of the supposedly aquatic rhinoceroses. True rhi- noceroses, that is animals which were directly ancestral to the modern members of the family, have not been identified and may not have been present in North America; that is still an open question. Tapirs, all of them quite small, were rel- atively common, but are still very incompletely known. The earliest known members of the clawed tchalicotheres were of Bridger date. It is worth remarking that, except a single genus in the upper and later portion of the stage (tTriplopus), all of the SUCCESSIVE MAMMALIAN FAUNAS 273 Bridger perissodactyls had four toes in the front foot and three in the hind, while in the White River beds above the lowest substage the number three in both fore and hind feet was almost equally universal. One of the most radical and striking differences between the Uinta and Bridger faunas was the rarity of Artiodactyla in the latter, which is in almost equally strong contrast with their abundance in the middle Eocene of Europe. Most significant of these rare Bridger artiodactyls were the little creatures (tHomacodon), hardly so large as a domestic cat, which may fairly be regarded as a very early stage, if not the actual beginning, of the great camel family, which was destined to play so conspicuous a part in the life of America, North and South. Small pig-like animals ({Helohyus) which were no doubt ancestral to the peccaries, were fairly common and there were, in addition, relatively large animals (tAchenodon) allied, but not ancestral, to the jgiant-pigs of the Oligocene ; some of these were considerably larger than a full-grown Wild Boar (Sus scrofa). Among all the many hoofed mammals of the Uinta and Bridger there was not a single one that had the high-crowned, persistently growing teeth of the grazers ; all of them must have had browsing habits and have fed upon such soft vegetable tissue as did not rapidly abrade the teeth. The same state- ment applies, 4 fortiori, to the stages antecedent to the Bridger and therefore to the entire Eocene and Paleocene. From these facts it may be inferred that the grasses had not yet taken possession of wide areas. Concerning the Bridger fauna, Professor Osborn, who has done so much to elucidate it, says: “On the whole, it is a very imposing, diversified and well- balanced fauna, with an equal distribution of arboreal, cur- sorial, aquatic, fossorial, carnivorous and herbivorous types.” The lower Eocene is divisible into two stages, in descending order, the Wind River and Wasatch, both extensively exposed in central Wyoming. As would be expected from its strati- T 274 LAND MAMMALS IN THE WESTERN HEMISPHERE graphical position, the Wind River fauna was largely transi- tional between that of the Bridger above and that of the Wasatch below. Unfortunately, the fossils are far less numer- ous than those of the Bridger and not so well preserved, and therefore give us a less adequate conception of the life of that time. The archaic, non-progressive orders were strongly represented, but already the progressive groups were in a numer- ical majority of species; most of these archaic orders may be most advantageously described in connection with the Wasatch. Opossums were almost certainly present, though the available specimens are too fragmentary for assured determination. The ftillodonts, fteniodonts and insectivores differed little from the Wasatch representatives of these orders, except that the Bridger {teniodont, {Stylinodon, which had rootless, persistently growing teeth, was associated with the Wasatch genus {Calamodon. On the other hand, the primitive flesh- eaters, or tereodonts, which were referable to Wasatch families, were less numerous and varied and formed a mixture of Bridger and Wasatch genera. The tOxyznide, the family with cat- like teeth and head, had both the smaller Wasatch genus +Oxyena and the very large Bridger }Patriofelis. Of the blunt-toothed +Mesonychide, one very large animal ({Pachy- ena) survived from the Wasatch. The small forms of the family tHyzenodontide were common, and there were numerous species of the progressive family }Miacide. Among the hoofed animals there were two of the antique orders which became extinct before the end of the Eocene, indeed, one of these groups, the +Condylarthra, made its last appearance in the Wind River. This extremely primitive group, which, in a sense, connected the hoofed with the clawed mammals, will be described under the more ancient faunas. The other order, the fAmblypoda, was represented by two very different families, one of which, the fuintatheres, was so flourishing in the Bridger, where it formed the most char- acteristic and by far the most striking element of the fauna. SUCCESSIVE MAMMALIAN FAUNAS 275 The Wind River genus ({+Bathyopsis) was a very much smaller animal than any of the Bridger forms and its horn-like pro- tuberances were in an incipient state, while in various other respects it was decidedly more primitive than its successors. The second family was represented by the genus tCoryphodon, which did not survive into the Bridger, but was especially characteristic of the Wasatch fauna, with which it will be described. Turning now to the progressive orders, we note that the rodents, lemurs and monkeys were very similar to those of the Bridger and belonged to the same families, but were decidedly less numerous. This difference, however, may be rather apparent than real and due to the much more favourable conditions for the preservation of small mammals in the middle Eocene. Among the Perissodactyla, the horses were inter- mediate in size and structure between those of the Bridger and thoseof the Wasatch, but were decidedly nearer to the latter. The {lophiodonts, so far as known, were represented by a single genus ({Heptodon) which also occurred in the Wasatch. The modest beginnings of the ftitanotheres, the family which be- came so very conspicuous in the middle and upper Eocene and lowest Oligocene, may be noted in the Wind River fauna, in which there were two genera. One of these ({Kotitanops), the very probable ancestor of all the subsequent genera, was quite small, about two-thirds the size of a modern tapir, while the other (tLambdotherium) was a much smaller, lighter and more slender animal and apparently belonged to an abortive, short-lived phylum. Then, too, the first of the fhyracodonts, or cursorial rhinoceroses, made their appearance here in the genus tHyrachyus, which was afterward so common in the Bridger. No Artiodactyla have yet been found in the Wind River, though there can be little doubt that they then inhabited North America, as they did both before and afterward. The Wind River fauna was of so much less peculiar and 276 LAND MAMMALS IN THE WESTERN HEMISPHERE isolated character than that of the Bridger as to suggest a connection with the eastern hemisphere, a suggestion which is strengthened by the unheralded appearance of the {titano- theres and thyracodonts, of which no forerunners have been found in the Wasatch. The lowest and most ancient of the Eocene faunas is that of the Wasatch formation, which is extensively developed in central and southern Wyoming, Utah and New Mexico. The fauna of this stage is plainly divisible into two groups: (1) those types which were the descendants of American Paleocene mammals and were therefore indigenous, and (2) the immigrants from other continents. The indigenous mammals, which almost all belonged to orders now extinct, few of which survived later than the Eocene, must have given a very bizarre appearance to the assemblage, especially as they were more numerous, varied and, for the most part, larger and more conspicuous than the newcomers. Marsupials have not yet been found, but the occurrence of opossums in the Bridger and probably in the Wind River gives some reason to believe that they were in North America during Wasatch times also. The fTzniodontia, which bore a certain resem- blance to South American edentates, had one pair of incisor. teeth above and below enlarged and chisel-shaped, somewhat like those of rodents. The tTillodontia were much smaller than those of the Bridger, and their incisors were only beginning to take on the chisel-likeform. Insectivora were quite abundant, and three, or perhaps four, families were represented in the Wasatch; some of these resembled the modern aquatic in- sectivores of the west African rivers and others were more like European hedgehogs. The flesh-eaters all belonged to the tCreodonta, and, though rather less diversified than those of the Bridger, were yet relatively abundant. In size, they ranged from little creatures not larger than a weasel up to truly enormous beasts, and differed, no doubt, largely in habits and manner of life. SUCCESSIVE MAMMALIAN FAUNAS 277 For the most part, the families were the same as those of the Bridger fcreodonts, but the genera all were different. The foxyznids ({Oxyena) were much smaller and lighter than the large and massive representatives found in the middle Eocene, and their teeth were not so cat-like. Another group of pre- daceous animals ({Paleonictis) which also inhabited Europe, but did not survive the lower Eocene in either continent, had short, broad and very cat-like heads. The tmesonychids were far larger than those of the Bridger, a departure from the ordinary rule, and the several species of the common Wasatch genus (fPachyena) had grotesquely large heads. A family (tArctocyonide), of very extensive geographical range and great antiquity, had its last representatives here in a very curious animal (fAnacodon) which had the flat-crowned, tuberculated grinding teeth of the bears and the enlarged, scimitar-like upper canines of the tsabre-tooth cats. Such a combination seems utterly incongruous and no one would have ventured to predict it. The progressive family of tere- odonts (fMiacide) was already quite numerously repre- sented, but only by small forms, which must have preyed upon small mammals, birds and lizards. Two archaic orders of hoofed mammals were fairly numer- ous. One, the {Condylarthra, comprised quite small, five- toed animals, with long tails and short feet and extremely primitive in structure. A genus (}Phenacodus) of this order was long regarded as being ancestral to most of the higher orders of ungulates, but this belief has proved to be untenable. More numerous were the tAmblypoda, one genus of which (tCoryphodon), though persisting into the Wind River, was especially characteristic of the Wasatch. The tcoryphodonts were the largest of lower Eocene mammals, and some of the species equalled a tapir or small rhinoceros in length and height, but had heavier limbs; as the skeleton conclusively shows, these must have been heavy, clumsy and exceptionally ugly brutes, with formidable tusks, large head, but relatively more LAND MAMMALS IN THE WESTERN HEMISPHERE 278 *AIOYSIFT [VINYBN JO UNsnY UBOTOUTY oY} UI UOJZ[OYS B WOJJ palo}sey “BIYVIE[APUOD| oy} Jo oATye}UOSeIdeI YO}BER MA UMOUY 980q oY} ‘snamwrid snpoopusyg| — “THT “OW wl. €F-6 1 a sav fHOl sansa le Si enn ee ee SUCCESSIVE MAMMALIAN FAUNAS 279 slender body, short and massive limbs and elephantine feet. In appearance, these strange beasts were not altogether unlike the Hippopotamus and were perhaps more or less amphibious in habits. The other family of ,Amblypoda, the tuintatheres, Rt - Broce HOonsFan oe Fic. 142. — The commonest of Wasatch ungulates, the tamblypod, tCoryphodon testis. Restored from a skeleton in the American Museum of Natural History. have not yet been registered from the Wasatch, but they will undoubtedly be found there, as they were unquestionably present at that time. All of the preceding groups were of the archaic, non- progressive type and have long been extinct. With the sole exception of one ftcreodont family (fMiacide#) and perhaps some of the insectivores, they have no descendants or repre- sentatives in the modern world. All of them appear to have been indigenous and derived from North American ancestors, though it is possible that a few were immigrants. We now turn to the orders which were more significant of the future, because they had within them the potency of a far higher development. These progressive groups were all immigrants, coming to North America from some region which cannot yet 280 LAND MAMMALS IN THE WESTERN HEMISPHERE be positively identified, but most probably was Asia. From the same region and at a corresponding period of time Europe received many of the same forms, and so many genera were at that time common to the latter continent and North America that a broad and easy way of intermigration must have been open. One of these immigrant orders, the Rodentia, the most ancient known members of which were these species from the North American Wasatch, was represented by the same family (fIschyromyide) and some of the same genera ({Paramys, {Sciuravus) as throve also in the Bridger stage. There were two orders of hoofed mammals, which were newcomers to the western world, Perissodactyla and Arti- odactyla. Of the former was a genus (tHohippus) of the most ancient American horses. These most interesting little ani- mals, no larger than small foxes and domestic cats, would hardly be called horses, were it not for the long series of gradual and successive modifications which led from +Hohippus up to the modern horses. The graceful little creatures had a short neck, curved back, and relatively short, slender limbs, with four functional toes in the front foot and three in the hind ; and, though they differed from existing horses in almost every detail of teeth and skeleton, there was something unmistakably equine about them. From the abundance of their remains it may be inferred that herds of them swarmed in the forests and glades of Wasatch times. The second perissodactyl family, the {Lophiodontide, which comprised considerably larger animals, never attained to importance in America, but flourished and became greatly diversified in Europe. What are believed to be the most ancient tapirs yet discovered ({Systemodon) were individually very common in the Wasatch. This tapir was no larger than a Coyote, had no proboscis and was so little like a tapir in outward appearance that an observer might well be pardoned for overlooking the relationship; even the skel- eton is of so indifferent a character that the reference of this genus to the tapirs cannot be positively made. SUCCESSIVE MAMMALIAN FAUNAS 281 Of equal significance for the future was the arrival of the Artiodactyla, of which there were members of three families in the Wasatch, though individually they were much less common than the horses. These were geologically the oldest known artiodactyls, Europe having yielded none of this date, and are still too imperfectly known to justify any very positive statements about them. One genus, however (fT rigono- lestes), tiny little creatures, like rabbits in size, would seem to represent the beginnings of the great ruminant tribe, now so very important a factor in the life of the world. A second genus ({Hohyus), considerably larger, is very doubtfully refer- able to the pigs; while a third (tParahyus), still larger, was the first in the short-faced series of the ftentelodonts, which persisted in ever increasing size through the whole Eocene, but could hardly have been ancestral to the true fentelodonts, or fgiant-pigs, of the Oligocene, the place and time of whose origin are unknown. Another immigrant order of great interest, since we our- selves belong to it, the Primates, made its first appearance in North America in the Wasatch, but was not destined to long life or great importance in this continent, where it did not survive the Eocene. Several different kinds of small, lemur- like and monkey-like creatures dwelt in the tree-tops of the Wasatch forests. One genus (tAnaptomorphus) had a remark- able likeness to the modern Tarsier (Tarsius spectrum) of the Malay peninsula and islands. South America. — The Eocene of South America, referred by some writers to the upper Cretaceous, is very incompletely and unsatisfactorily known. The Casa Mayor formation (or Notostylops Beds), which has yielded a great variety of mammals, for the most part very fragmentary, probably contains not one but several successive faunas which have not yet been fully discriminated, and that of the next succeed- ing Astraponotus Beds is still but a scanty list. This list, however, includes the most ancient tglyptodonts yet discovered 282 LAND MAMMALS IN THE WESTERN HEMISPHERE and the most ancient tastrapotheres in the narrow sense of the term. The Astraponotus Beds may be either Eocene or Oligocene in date. Taking the Casa Mayor faunas as a whole, they were a very numerous and diversified assemblage of small mammals, without a single large one among them. There were no monkeys or rodents; otherwise, the orders were in almost all cases the same as those which made up the Santa Cruz fauna. The marsupials were represented by the opossums and by several of the carnivorous kinds, the only beasts of prey that South America had until the migrations from the north brought in the true Carnivora, late in the Miocene or very early in the Pliocene. There were also numerous small marsupials of peculiar type, of which the last living survivor is Cenolestes, of Ecuador. Throughout the stage, armadillos were present in considerable variety, but are known only from the bony plates of the carapace, and therefore little can be determined as to their relationships to the modern families. Only a single and very problematical genus of the tground- sloths,. which afterwards throve so mightily in the Miocene and Pliocene, has been obtained and that in the later portion of the stage. The orders of hoofed mammals were represented by. many small animals, most of which are known only from the teeth, which show these Casa Mayor genera to have been far more primitive and less specialized than their descendants in the Deseado and Santa Cruz stages. All of them had the low- crowned grinding teeth of the browsers, and no grazers were then in existence, so far as is known. No ftoxodonts, in the more restricted sense of that term, have been found, but the two allied suborders of the +Typotheria and tEntelonychia were numerously represented. Of the former there were two families and of the latter three, which is more than in the Deseado or Santa Cruz formations. One of the families of the tEntelonychia (tNotostylopidx) consisted of very small, SUCCESSIVE MAMMALIAN FAUNAS 283 rodent-like animals, with a pair of chisel-shaped incisors in upper and lower jaw, and a second family ({Homalodonto- theriidg) contained genera which would seem to have been directly ancestral to those of the Santa Cruz, but were very much smaller than their successors. The very large and massive }Pyrotheria of the Deseado stage were represented by small animals, in which the grinding teeth had two pairs of conical tubercles, not yet united into transverse crests. Two families of the fastrapotheres, in the broad sense, were far smaller than their Oligocene and Miocene descendants. To the {Litopterna are referred a number of genera, in which the grinding teeth were tuberculated and had very imperfectly developed crests, so as strongly to suggest the teeth of the tCondylarthra. However, until something is ascertained re- garding the skeleton, especially the feet, of these animals, their relationships will remain more or less doubtful. It will be observed that these Casa Mayor faunas not only were made up exclusively of small animals, but also that they already were typically and characteristically ‘South American and bore the stamp which remained essentially the same until the successive waves of migration from the north so greatly modified the composition of the Neotropical fauna. The absence of rodents and monkeys and the com- parative unimportance of the Edentata gave a somewhat different character to these ancient faunas from those of the Santa Cruz and later formations. 5. Paleocene North America. — A very important discovery is one lately made by American Museum parties of a formation intermediate between the Wasatch and Torrejon. The interesting fauna of these beds has not yet been described, but it may be re- marked that it contained none of the immigrant orders. The vegetation of the Paleocene was already very mod- ern in character, and nearly all of the common forest-trees 284 LAND MAMMALS IN THE WESTERN HEMISPHERE were represented by species which differed but slightly from those of the present. The grasses were already in existence, but, there is good reason to believe, they had not attained to much importance and-did not cover the plains and open spaces as they did in the Miocene and still continue to do. As the grasses afford the principal food-supply of so many grazing animals, the matter of their abundance and extension is a very significant one in the history of mammalian develop- ment, and, as we have already learned, eventually led to wide- spread and profound modifications of structure, especially of the teeth. While there is thus nothing very strange about the plant-world of Paleocene times, the higher animal life was almost totally different from that of modern times and made up a most curious and bizarre assemblage, from which nearly all the familiar Recent types were absent. The reptiles had been greatly impoverished by the world-wide and, as yet, un- explained destruction which overtook them at the end of the Mesozoic era, but it is possible that in both North and South America a few of the huge Dinosaurs survived the decimation of the class. Very characteristic of the Paleocene in North America and Europe were large, lizard-like reptiles, allied to the New Zealand Tuatara, while crocodiles and tortoises abounded; snakes were present, but do not appear to have been very common. It is the mammals which were the strangest element of Paleocene life, and our imaginary observer would find no creature that he had ever seen before. The difference from modern mammalian life was not merely one of species, genera ° or even families, but of orders, for only one, or at most two, of the orders now living were then to be found in North America, and both of these (marsupials and insectivores) were primitive and archaic groups, which seem like belated survivals in the modern world. There were no rodents, or true carnivores, no lemurs, monkeys, artiodactyls, perissodactyls or proboscideans. In the Torrejon, or upper Paleocene, there were many SUCCESSIVE MAMMALIAN FAUNAS 285 herbivorous marsupials, with very complex grinding teeth and chisel-like incisors, but no carnivorous or insectivorous mem- bers of the order have been found. Insectivora were present. Of the fereodonts, or primitive flesh-eaters, there were no less than five families; the bear-like fArctocyonide, which died out in the Wasatch, were quite numerous, and the problematical tMesonychide were much smaller and more R-RuCE. Wlons FAL eered 9 fla Fic. 143. —The Torrejon forerunner (tPantolambda bathmodon) of *Coryphodon. Restored from a skeleton in the American Museum of Natural History. primitive mammals than those of the Eocene. Passing over two families which did not survive the Torrejon, we may note the first of the tMiacide, the progressive family which led eventually to the true Carnivora. The hoofed animals all belonged to the archaic {Condylarthra and tAmblypoda ; of the former there were many genera and species referable to three families, one of which contained the forerunners of the Wasatch {Phenacodus. The genus {Pantolambda of the Amblypoda may well have been ancestral to both the fcory- phodonts and the fuintatheres of the Eocene. 286 LAND MAMMALS IN THE WESTERN HEMISPHERE The Puerco fauna was much like that of the Torrejon, but even less advanced and diversified. The herbivorous marsu- pials were more abundant, and some of them (}+Polymastodon) larger than those of the Torrejon; Insectivora may have been present, but this is doubtful. The fcreodonts, so far as they have been discovered, were less numerous, varied and specialized than those of the Torrejon and included but one Fic. 144. — Head of an fallotherian marsupial ({Polymastodon tadensis) from the Puerco stage. Restored from a skull in the American Museum of Natural History. of the families which passed over into the Eocene. The +Condylarthra were much less common and the tAmblypoda but doubtfully represented, but the edentate-like }Tzniodontia were conspicuous. Not only were the Paleocene faunas radically different from the mammals of our time, but they could not have been ancestral to the latter, being hardly more than an advanced and diversified Mesozoic assemblage. It is true that some of its elements, such as the tCondylarthra, tAmblypoda and tCreodonta, developed greatly and played an important part SUCCESSIVE MAMMALIAN FAUNAS 287 in the life of the Eocene, but of these only a few fcreodonts continued into the Oligocene and all became extinct without leaving any descendants behind them.‘ Another curious fact concerning the Paleocene mammalian faunas is that they were made up entirely of small and very small animals; not a single mammal as large as a sheep has yet been found in these beds, and the same is true of Europe. That a land-connection with the Old World existed during the Paleocene epoch, is indicated by the similarity of the faunas of North America and Europe. CHAPTER VIII HISTORY OF THE PERISSODACTYLA In attempting to trace the evolutionary history of the various mammalian groups, it is necessary to bear in mind the inevitable limitations of work of this kind. Speaking of plants, Dr. D. H. Scott says: ‘‘Our ideas of the course of descent must of necessity be diagrammatic; the process, as it actually went on, during ages of inconceivable duration, was doubtless in- finitely too complex for the mind to grasp, even were the whole evidence lying open before us. We see an illustration, on a small scale, of the complexity of the problem, in the case of domesti- cated forms, evolved under the influence of man. Though we know that our cultivated plants, for instance, have been developed from wild species within the human period, and often within quite recent years, yet nothing is more difficult than to trace, in any given instance, the true history of a field- crop or garden plant, or even, in many cases, to fix its origin with certainty.””! With some mammalian groups the task, though difficult enough, is not so hopeless, because of more complete records, yet in dealing with mammals a very trouble- some complication is introduced by the existence within the families, and even within the genera, of two or more parallel phyla, or genetic series. Without complete and perfect mate- rial it is impossible to make sure that we are not confusing the different phyla with one another and placing in one series species and genera that properly belong in a different one. Thus, Osborn distinguishes no less than seven such phyla 1D. H. Scott, Studies in Fossil Botany, London, 1900, pp. 524-525. 288 HISTORY OF THE PERISSODACTYLA 289 among the true rhirioceroses of the Old and New Worlds, which long followed parallel, but quite independent, courses of development, and five phyla among the American horses. While these phyla add so much to the dif- ficulty of working out the genealogi- cal series, it is possible to simplify the problem and treat it in a broad and comprehensive manner that will sufficiently establish the essen- tial steps of change. In external appearance and gen- eral proportions the different fami- lies of existing perissodactyls. have very little in common; that tapirs and rhinoceroses should be related is not surprising, but the horses would seem to be as far removed from both of the former as possible. Why, then, should they be included in the same order? A study of the skeleton, however, reveals the com- munity of structure which obtains between the three families, a com- munity which removes them widely from all other hoofed mammals. In all existing perissodactyls, though not in most of the Eocene genera, all the premolars, except the first, have the size and pattern of the molars. The foramina of the skull, or per- Fic. 145.— Left manus of Tapir (Tapirus terrestris). S., scaph- oid. LZ., lunar. Py., pyramidal. Pis., pisiform. Td., trapezoid. M., magnum. Un., unciform. The metacarpals are erroneously numbered. Me. I., second met- acarpal. Mc. II., third do. Mc. IlI., fourth do. Mc. IV., fifth do. Ph. 1, first phalanx. Ph. 2, second do. Ung., un- gual phalanx. forations by which blood-vessels and nerves enter and leave the cranium, are arranged in a way characteristic of the order and different from that seen in other hoofed mammals. The number of digits in each always has the third trochanter. U The femur 290 LAND MAMMALS IN THE WESTERN HEMISPHERE foot is usually odd, 1, 3 or 5, but four- toed forms occur, as the tapirs, which have four toes in the front foot, three in the hind; the important character is that the median plane of the foot bisects the third digit, which is sym- metrical. The third and fourth, each asymmetrical, together form a sym- metrical pair. Especially ‘character- istic is the form of the astragalus and calcaneum (ankle and heel bones) ; the astragalus has but a single, deeply grooved and pulley-like surface, that for the.tibia, the lower end is nearly flat and rests almost entirely upon the navicular, covering but little of the cu- boid (see Figs. 146, 148). The cal- ’ caneum does not articulate with the <4) fibula and its lower end is broad and covers most of the cuboid. While the foregoing list includes the most important of the structural features which are common to all perissodactyls and differentiate them Fie. 146.—Left pes of Tapir. Cal., calcaneum. As., astrag- {rom other hoofed animals, there are alus. N., navicular. Cn. 1, many others which it is needless to Cn. 2, Cn. 3, first, second and third cuneiforms. Mr. II, 111, enumerate. IV, second, third and fourth = The subjoined table gives the metatarsals. te ad families and principal genera of the American Perissodactyla; extinct groups are marked f. Suborder CHELODACTYLA. Normal Perissodactyls I. Equipz. Horses. { Eohippus, low. Eoc. tOrohippus, mid. Hoc. ft Epihippus, up. Koc. +Mesohippus, low. Oligo. {tMiohippus, up. Oligo. fAnchithe- rium, up. Oligo. t+ Parahippus, low. Mioc. to low. Plioc. Des- HISTORY OF THE PERISSODACTYLA 291 matippus, mid. Mioc. ft Hypohippus, mid. Mioc. to low. Plioc. {Merychippus, mid. Mioc. to low. Plioc. Protohippus, up. Mioc. }Pliohippus, up. Mioc. and low. Plioc. + Neohipparion, up. Mioc. and low. Plioc. {Hipparion, Plioc. t Hippidion, Pleist., S. Amer. tHypernippidium, Pleist.,S8.Am. Equus, Pleist., N. and S. Amer. II. ¢Trranotuerup#. fTitanotheres. {Lambdotherium, low. Eoc. {Eotitanops, low. Eoc. ft Paleosyops, mid. Eoc. {Telmatherium, mid. Eoc. f{Dolichorhinus, up. Eoc. {Diplacodon, up. Eoe. f Titanotherium, low. Oligo. Ill. Tarrria. Tapirs. {Systemodon, low. Eoc. fIsectolophus, mid. and up. Eoc. fPro- tapirus, Oligo. +Tapiravus, mid. Mioc. Tapirus, Pleist., N. Amer., Pleist. and Recent, S. Amer. IV. tLopaiopontipx. tLophidonts. | Heptodon, low. Eoc. f Helaletes, mid. Eoc. tColodon, low. Oligo. V. Rarnocerotip#. True Rhinoceroses. ‘ tTrigonias, low. Oligo. +Cenopus, Oligo. and low. Mioc. {Dice- ratherium, up. Oligo. and low. Mioc. tAphelops, mid. -Mioc. to low. Plioc. tT eleoceras, mid. Mioc. to low. Plioc. VI. tHyracopontipa. tHyracodonts and fAmynodonts, cursorial and aquatic Rhinoceroses. + Hyrachyus, low. and mid. Eoc. t{Triplopus, mid. and up. Eoc. {Colonoceras, mid. Eoc. + Hyracodon, low. Oligo. tAmynodon up. Eoc. {Metamynodon, low. Oligo. Suborder fANCYLOPODA. fClawed Perissodactyls VII. ¢ CHanicotaermps. Chalicotheres. {Moropus, up. Oligo. and low. Mioc. ?tSchizotherium, low. Oligo. {Homoropus, mid. Eoc. The earliest perissodactyls of which we have any knowl- edge are found in the older part of the lower Eocene (Wa- satch stage) of Europe and North America, into which they must have migrated from some other region yet unknown, for no probable ancestors of the group are found in the Paleo- cene of either continent. I. SuBporpER CHELODACTYLA. NorRMAL PERISSODACTYLA. 1. Equide. Horses In order to make intelligible the evolutionary changes which have led up to the modern horses, it will be necessary to say something concerning the dental and skeletal features which 292 LAND MAMMALS IN THE WESTERN HEMISPHERE characterize these animals. Using the term horses in a broad sense to include all the existing members of the family Equide, true horses, asses, zebras and quaggas, we find a greater uniformity in the skeleton and teeth than would be expected Fic. 147. — Asiatic Wild Horse (Equus przewalskit). — By permission of the N.Y. Zoolog. Soc. from the external appearance. The differences in appearance are, however, largely due to colouring, growth of mane and- tail and the size of the ears, which leave no record in the skeleton. The teeth (Figs. 45, p. 95; 154, p. 306) are extremely high- crowned, or hypsodont, and do not form roots till an advanced age; the incisors have a deep, enamel-lined pit, the ‘‘mark”’ in the centre of the grinding surface; the first premolar in each jaw is very small and of no functional importance; the other premolars have the same pattern as the molars, which is excessively complex in the arrangement of the enamel ridges and the areas of dentine and cement. The skull (Fig. 154, p. 306) is long, especially the facial por- tion, the eye-socket (orbit) being shifted behind the teeth, which HISTORY OF THE PERISSODACTYLA 293 otherwise, on account of their great height, would press upon the eye itself; the orbit is completely encircled in bone. The lower jaw is deep vertically and the ascending ramus (see p. 66) ‘very high, on account of the hypsodont character of the teeth, which thus necessitates a remodelling of the skull in several respects. The neck is long, each of its seven vertebre being elongate; except in the atlas and axis, the anterior face of each centrum is strongly convex and the posterior of all except the atlas is deeply concave; the odontoid process of the axis (see p. 71) is spout-shaped, concave on the upper and convex on the lower side, lodging and protecting the spinal cord. The spines of the anterior dorsal vertebre are very high, making a low hump at the withers between the shoulder-blades; the trunk-vertebre are so arranged as to make the back almost straight and horizontal. The limbs and especially the feet are very long. z The two bones of the fore-arm, the ulna and radius, are codssified into a single piece (Fig. 30, p. 81), but the limits of each are still plainly to be seen, especially in a young animal; and it is evident that the ulna is greatly re- duced in size and has lost its middle portion, while all the weight is borne by the radius. Similarly, in the hind leg the enlarged tibia, or shinbone, alone supports the weight; and only the two ends of the fibula are preserved (Fig. 38, p. 87), and these are indistinguishably fused with the tibia in the adult animal, but may be made out in the colt. The thigh- bone has a very characteristic shape, which is difficult to de- scribe without an undue use of technical terms, but the unusual prominence of the great trochanter (Fig. 35, p. 85) and of the rotular groove is an important factor in producing this ap- pearance. The very long and slender feet are so raised from the ground that the animal walks upon the very tips of the toes, the wrist being what horsemen call the ‘‘knee” and the heel is the “hock,” and the gait is thoroughly unguligrade. Each foot has but a single functional toe, the third or middle one of the 294 Fie. 148. — Left pes of Horse. Cal., cal- caneum. As., as- tragalus. N., navic- ular. Cn. 3, third cuneiform. Mt. III, functional (third) metatarsal. Mt. II and Mt. IV, splints. lateral dislocation. mals this keel is merely a projec- tion from the lower articular sur- face and is confined to the pos- terior side, so as not to be visible The terminal or un- gual phalanx is much enlarged to carry the great weight which it sup- from the front. LAND MAMMALS IN THE WESTERN HEMISPHERE primitive five-toed foot ; and, as this toe has to carry the whole weight supported by its leg, it is necessarily much larger than in ani- mals which distribute the weight among sev- eral digits. The horses are therefore said to be monodactyl, or single-toed, but the term is not strictly accurate, for on each side of the functional digit is a rudimentary or ves- tigial one, the 2d and 4th of the original five. These rudimentary digits, which are not visi- ble externally, have no phalanges and are merely ‘‘splint-bones,’”’ metapodials (see p. 90) which have very slender shafts and end below in blunt points. The sin- gle functional metapodial has encircling its lower articular end a prominent ridge or keel, which fits into a corresponding groove on the up- per end of the first phalanx and serves to prevent In most mam- Fic. 149.— Left manus of Horse, front side; to the right, rear view of the metacarpus. ., scaphoid. L., lunar. Py., pyramidal. Pis., pisiform. Td., trapezoid. M, magnum. U., unciform. Mc. II, Mc. IV, rudimentary second and fourth metacarpals, or splints. HISTORY OF THE PERISSODACTYLA 295 ports and is enclosed in the characteristic hoof, unlike that of any other mammal. In brief, the whole structure of the horses is pre-eminently adapted to swift running; they are admirable ‘‘cursorial machines,” as they have been called, and every part of the skeleton has been modified and specialized to that end; the narrow, rigid hoofs fit them for walking on firm ground and they speedily are made helpless in quicksand or bog. Did we know nothing of their mode of life, we might confidently infer from their teeth that the horses were grazers, feeding prin- cipally upon grass. A long-legged, grazing animal must needs have a neck of sufficient length to enable the mouth to reach the ground easily, unless a long proboscis is developed ; and so we shall find in the history of the horses that the elongation of the head and neck kept pace with the lengthening of the legs and feet. Though it can hardly be doubted that the horses passed through most of their development in North America, yet the immediate ancestry of all the existing species must be sought in the Old World, none of the many Pleistocene species of the western hemisphere having left any descendants. In North America all of the known Pleistocene forms belonged to the genus Equus, but the True Horse, EF. caballus, was not among them. The more abundant and important of these species have been sufficiently described in Chapter VII (p. 199); it need only be recalled that there were ten or more distinct forms, ranging in size from the great EH. tgiganteus of Texas to the minute E. ttau of Mexico, while the plains and forests were the feeding grounds of moderate-sized species, about 14 hands high. In the latest Pliocene, and no doubt earlier, species of the modern genus Equus had already come into existence; and in association with these, at least in Florida, were the last. sur- vivors of the three-toed horses which were so characteristic of the early Pliocene and the Miocene. However, little is known 296 LAND MAMMALS IN THE WESTERN HEMISPHERE about those earliest recorded American species of Equus, for the material so far obtained is very fragmentary. In the ab- sence of any richly fossiliferous beds of the upper Pliocene generally, there is a painfully felt hiatus in the genealogy of the horses ; and it is impossible to say, from present knowledge, whether all of the many species of horses which inhabited North America in the Pleistocene were autochthonous, derived from a purely American ancestry, or how large a proportion of them were migrants from the Old World, coming in when so many of the Pleistocene immigrants of other groups arrived. It is even possible, though not in the least likely, that all of the native American stocks became extinct in the upper Pliocene and that the Pleistocene species were all immigrants from the eastern hemisphere, or the slightly modified descendants of ‘such immigrants; but, on the other hand, it is altogether prob- able that some of these numerous species were intruders. Un- fortunately we are in no position yet to distinguish the native from the foreign stocks. " In themiddle Pliocene, which also has preserved but a meagre and scanty record of its mammalian life, we again meet with horses in relative abundance, but of a far.more primitive type. They are still incompletely known, but it is clear that they belonged to three parallel series, or phyla, of three-toed grazing horses, with teeth which, though high-crowned, had: not at- tained to the extreme degree of hypsodontism seen in the species of Hquus and had a somewhat less complex pattern of the grinding surface, though distinctly foreshadowing the modern degree of complication. One of the genera (}Plio- hippus) was not improbably the ancestor of a very peculiar horse ({Hippidion) of the South American Pleistocene. These middle Pliocene genera were much smaller animals than the Pleistocene horses, aside from the pygmy species of the latter, of light and more deer-like proportions, and with three func- tional toes or digits. The median digit (3d of the original five) was much the largest and carried most of the weight, on HISTORY OF THE PERISSODACTYLA 297 hard ground practically all of it; the lateral digits (2d and 4th) which in existing horses are represented by the rudimen- tary metapodials, or ‘‘splints,” though much more slender than the median digit, yet had the complete number of parts and each carried a small hoof. Mere ‘‘dew-claws”’ as these lateral toes were, they may have been of service in helping to support the weight in mud or snow. In all parts of the skele- ton there are little details which show that these species of the middle Pliocene were not so advanced and differentiated as are their modern successors, but it would be unprofitable to enumer- ate these details, which are of interest only to the anatomist. In the lower Pliocene the horses were very much more numerous and varied than in the middle portion of the epoch. The same three genera of grazing animals, represented by less advanced and modernized species, are found ; and, in addition, there was an interesting survival ({Merychippus) from the middle Miocene of an intermediate type, together with several species of browsing horses ({Parahippus and +Hypohippus). In these browsing forms the teeth were all low-crowned and early formed their roots, and the crowns were either without cement or with merely a thin film of it in the depressions of the grinding surface. The pattern of the grinding surface is so very much simpler than in the high-crowned, prismatic teeth of the grazers that it requires close analysis to detect the fundamental identity of plan. Such teeth imply that their possessors must have fed habitually upon a softer and less abrasive diet than grass, probably the leaves and soft shoots of trees and bushes and other succulent vegetable substances, very much in the fashion of existing deer, and must therefore have been chiefly inhabitants of the woods and groves and thickets along streams, as the grazing species were of the plains and open spaces. ‘‘This assemblage of the progressive and conservative types of horses was certainly one of the most distinctive features of Lower Pliocene time in North America ”’ (Osborn). 298 LAND MAMMALS IN THE WESTERN HEMISPHERE In the upper Miocene very much the same conditions pre- vailed and, for the most part, the same genera of horses, with different and somewhat less advanced species, were found as in the lower Pliocene, so that no particular account of them is T-BRUCE HORSPAL sa - Sih ¥ oy3 = Fig. 150. — Three-toed, grazing horse ({ Neohipparion whitney?) of the upper Miocene. Restored from skeletons in the American Museum of Natural History. needed. In the middle Miocene, however, there was a change, the typically grazing horses being very rare or absent and those with intermediate forms of teeth taking their place. Evi- dently, it was about this time that the horses with more plastic organization and capable of readjustment to radically different conditions began to take to the grazing habit, while other phyla, less capable of advance, retained the ancient, low- crowned type of grinding teeth and, after persisting, as we have seen, into the lower Pliocene, became extinct before the middle of that epoch. It is of great interest to observe that in the genus ({Merychippus) iritermediate between the browsing and grazing types, the milk-teeth retained the older and more prim- itive character of low crowns without covering of cement, HISTORY OF THE PERISSODACTYLA 299 while the permanent grinders had much higher, cement-covered and complex crowns. In the lower Miocene, the variety of horses was much diminished and all had the low-crowned, cement-free, browsing type of teeth. Reversing the statement, we see that in the middle and still more in the upper Miocene Fic. 151. —Skeleton of t Neohipparion whitneyi, American Museum. the primitive and more or less distinctly homogeneous phylum branched out into several series, like a tree, some of the branches continuing and further subdividing through the Pliocene and Pleistocene, while others, less progressive and less adaptable, underwent but little change and had died out before the middle Pliocene. The Oligocene horses deserve more particular attention, for they were almost the half-way stage of development in the long backward ascent to the earliest known members of the family in the lower Eocene. We may pass over the John Day horses (tMiohippus), which were somewhat larger than those of the White River, but otherwise very like them, merely noting the presence of a slightly different genus (tAnchitherium) 300 LAND MAMMALS IN THE WESTERN HEMISPHERE which was the probable ancestor of tHypohippus and the other non-progressive types of the Miocene and Pliocene. The genus ({Mesohippus) which characterizes the White River, or lower Oligocene, was a group of species of different sizes, becoming smaller as we go back in time, the commonest one being con- siderably smaller than a sheep and differing more or less in all Fic. 152. —The small, browsing, three-toed, short-necked horse (t Mesohippus bairdi) of the middle White River. Restored from a skeleton in the American Museum. its parts from the horses of the upper Miocene and all subse- quent formations. The teeth were very low-crowned and fitted only for the mastication of soft vegetable tissue ; but it is of particular interest to observe the beginnings of the ‘‘mark”’ in the upper incisors in the form of a low enamel-ridge arising behind the cutting edge of the tooth ; the lower incisors still had the simple chisel-like crowns of the more ancient genera; all the premolars, except the first, had already acquired the molar-pattern. The skull resembled that of a very small modern horse, but with many differences of detail, the most obvious of which is the shallowness of the jaws, for depth was not needed to HISTORY OF THE PERISSODACTYLA 301 carry the very low-crowned teeth, and, for the same reason, the ascending ramus of the lower jaw was short. The face was relatively short and the eye-socket, which was incompletely surrounded by bone, was directly above the hindmost teeth ; the cranium was proportionately large and capacious and the brain, as is shown by the cast, was richly convoluted. The neck was relatively far shorter than in the Miocene genera, the ball-and-socket joints between its successive vertebra were less elaborated and the odontoid process of the axis was in the first stage of assuming the spout-like form, being semi- cylindrical, with convex lower and flat upper surface. The trunk was proportionately long and the back sloped forward, owing to the greater length of the hind legs. The limbs and feet were elongate and very slender, but the fore-arm bones are only partially codssified, and the ulna, though greatly attenuated, was still complete. The same is true of the bones of the lower leg; the shaft of the fibula was hardly more than a thread of bone, but its full length was preserved. In the fore foot there were three functional digits, the median one enlarged and supporting most of the weight, but its hoof was much thinner and flatter than in the corresponding digit in the Miocene and subsequent genera; the lateral digits touched the ground and were not entirely functionless and, in addition, there was a small splint, the rudiment of the fifth digit. The hind foot was three-toed, without splint. The little Uinta horse ({Epihippus) is still very incompletely known, but gives us one point at least of greater primitiveness than the White River genus in that only the last two premolars had taken on the molar-pattern, the forward two being smaller and simpler. The known species of the Uinta genus was very much smaller than any of the White River forms and even smaller than some of those of the preceding Bridger formation ; but it should be remembered that the Uinta has been but par- tially explored and much remains to be learned regarding its fauna. 302 LAND MAMMALS IN THE WESTERN HEMISPHERE The Bridger horses are fortunately much better known. There are several species of the genus tOrohippus, which form. a connected and progressive series ; and, though much smaller than the smallest and oldest of the White River forms, they were somewhat larger than the known representative of the Uinta, tEpthippus, but distinctly more primitive in all other respects. The incisors were simple cutting teeth, with no trace of even an incipient ‘‘mark,’’ and only one premolar in each jaw, the hindmost one, had taken on the molar-pattern. The orbit was farther forward in the skull and less enclosed behind than in {Mesohippus, the cranium narrower and less capacious; the neck was even shorter and the odontoid process of the axis still retained the primitive peg-like form. The limbs and feet were conspicuously shorter in proportion than those of the White River genus; the ulna and fibula were stouter and less reduced and entirely separate from the radius and tibia respectively. The front foot had four functional toes; the fifth digit, which in {Mesohippus had been reduced to a splint, was completely developed in the Bridger horses, but the hind foot was three-toed. . Passing over, for lack of space, the transitional forms of the Wind River, we come finally to the most ancient known horses, the Wasatch species comprised in the genus }Hohippus, the ‘‘Dawn Horse,” as its name signifies; these were little creatures ranging in size from a cat to a small fox. Despite an unmistakably equine look in the skeletons of these di- minutive animals, it is only the long intermediate series of species and genera, together forming a closely linked chain, which we have traced back from the Pleistocene to the lower Eocene, that leads us to regard {Hohippus as the ancestral type of the horses. Were only the two ends of the chain known, he would be a daring ‘speculator who should venture to connect them. In these little Wasatch horses we have the evidence of,a still more ancient form with five fully developed toes in each foot, since the front foot had four HISTORY OF THE PERISSODACTYLA 303 functional digits and indication of a splint, and _ splints, as the whole history of the long series teaches, always are found to be functional digits in the ancestor ; the hind foot had three toes and perhaps two splints. This preceding form is hardly to be looked for in America or Europe; it will be found, if ever, in the region whence the great migration came. TPBRUCE HORSFALL (ay = _ Fic. 153. — The ‘‘Dawn Horse " (tEohippus) of the lower Eocene. Restored from a skeleton in the American Museum. In all other respects, as well, tHohippus was what we should expect the forerunner of the Wind River and Bridger horses to be. The premolars were all smaller and simpler than the molars and the latter in the upper jaw are particularly interest- ing, for they had no crests and ridges of enamel, but four prin- cipal conical cusps, arranged in two transverse pairs, and be- tween the cusps of each pair was a tiny cuspule no bigger than the head of a pin. These cuspules were the first step in the for- mation of the transverse crests, which were destined to assume such importance in the subsequent members of the series. The 304 LAND MAMMALS IN THE WESTERN HEMISPHERE neck was very short, the body long, with curved or arched back, the limbs and feet short, and the hind limb much longer than the fore, making the relative proportions of the various parts of the skeleton very different from what they afterwards became. Reviewing this marvellous history of steady and long-con- tinued change, beginning with the most ancient genus, {Hohip- pus, the following modifications may be noted : (1) There was a nearly constant, if somewhat fluctuating, increase in size, leading by slow gradations from the diminutive horses of the lower Eocene to the great animals of the Pleis- tocene. (2) The molar teeth, originally made up of conical cusps, changed to a highly complex pattern of crests and ridges, and the premolars, one by one, assumed the size and pattern of the molars; the low-crowned, rooted and cement-free teeth, fitted only for browsing, became very high-crowned, prismatic and cement-covered, admirably adapted to grazing. Beginning in the upper incisors of the White River tMesohippus, the “mark”’ became established as an enamel-lined pit, growing in depth as the teeth increased their length. (3) The face grew relatively longer, the eye-socket being shifted behind the teeth and becoming completely encircled in bone, and the jaws were greatly increased in depth to ac- commodate the very long teeth. (4) The short neck was greatly elongated and the individual vertebree modified so as to give flexibility with no loss of’ strength. The primitive peg-like odontoid process of the axis became first semicylindrical and then spout-shaped. (5) The arched back was straightened and the neural spines, especially of the anterior dorsals, elongated. (6) The limbs grew relatively much longer ; the bones of the fore-arm and lower leg were fused together, the one on the inner side (radius and tibia) enlarging to carry the entire weight and the external one (ulna and fibula) becoming more or less atrophied. HISTORY OF THE PERISSODACTYLA 305 Fic. 154.— Series of horse skulls in ascending geological order. A., | Eohippus, lower Eocene (after Cope). B., t Mesohippus, lower and middle Oligocene. C., + Proto- hippus, upper Miocene (after Cope). D., Equus. x *. 306 LAND MAMMALS IN THE WESTERN HEMISPHERE (7) The feet were much elongated and the median (3d) digit of each gradually enlarged until it carried the whole Fic. 155. — Right manus and left pes of Fra. 156. — Right manus and left pes of Equus. + Protohippus. weight, at the same time modifying the shape of the hoof so as to fit it to be the sole support of the body. The other toes gradually dwindled and became functionless, though often retained as splints. The first digit (pollex and hallux) was first HISTORY OF THE PERISSODACTYLA 307 lost, then the fifth, then the second and fourth were reduced to dew-claws and finally to splints. Thus the pentadactyl horses of the lower Eocene were transformed into the monodactyl species of the Pliocene and Pleistocene. In South America the story of the horses was a brief one, for they were among the immigrants from the north and did not reach the south- ern continent till the Plio- cene, probably late in that epoch, for none of the three- toed genera have been found in South America. So far Fie. 157. — Right Fig. 158. — Right as known, these southern manus and left pes manus and pes of ; { tMesohippus. Eohippus. equines were small and me- ™ “Pus imenreaee dium sized animals, with large heads, relatively short feet and somewhat ass-like proportions. There were two well- defined groups of these animals: (1) species of the genus Equus, which thus, at one time or another, inhabited every one of the continents, Australia excepted; (2) three gen- era peculiar to South America and developed there from northern ancestors, probably }Pliohtppus. Two of these genera (t{Hippidion and {Onohippidium) displayed curious modifications of the nasal bones, which were extremely slender and attached to the skull only at their hinder ends, instead of being, as is normally the case, supported for nearly their whole length by lateral articulation with other bones. What can have been the significance and function of these excessively slender, splint-like nasals, it is difficult to conjecture. The third genus (tHyperhippidium) was a small mountain-horse, with extremely short feet, which were well adapted to climbing. This is the merest outline sketch of a most wonderful series 308 LAND MAMMALS IN THE WESTERN HEMISPHERE of gradual and progressive modifications, a sketch that might readily be expanded into a volume, were all the details filled in. While each set of organs, teeth, skull, neck, body, limbs and feet, might appear to advance independently of the others, COMIN 4 \ . or Dd, S S. Dy Fig. 159.——Skeleton of a Pampean horse (t Hippidion neogeum), National Museum, Buenos Aires. For restoration, see Fig. 119, p. 214. Note the splint-like nasal bones attached only at the hinder end. in reality there was no such independence, for at every stage of the progression all the parts must have been so codérdinated into a harmonious whole, that the animal could thrive and hold its own in the stress of competition. Could we but dis- cover all the. facts of environment, on the one hand, and or- ganization, on the other, we should doubtless learn that the little {Hohippus was as exquisitely fitted to its place in the Wasatch world, as are the horses, asses and zebras of the present day to theirs. It was the response to changing needs, whether of food, climate, disease or competition, that was the main factor of development. 2. tTitanotheriide. +Titanotheres This family, all of whose members vanished from the earth ages ago, was a comparatively short-lived group and nearly the whole of its recorded history was enacted in North America ; 309 HISTORY OF THE PERISSODACTYLA -WoUry oy} Ul 04d] *AI09STZ [BINYV NY JO uNasnyA, UB YS BUMIOI; paroysoy “Fu YRY sopeur (wnpsnqgos wnrsayjounjrF, |) atoyJOUeyN} | JOATY AIT AA — ‘OOT “PUT 310 LAND MAMMALS IN THE WESTERN HEMISPHERE only a few belated stragglers reached the eastern hemisphere, though the family may, nevertheless, have originated there. In the lowest of the three substages of the White River Oligocene the most conspicuous and abundant fossils are the {titanotheres, the latest members of which were huge animals of almost elephantine proportions. They belonged to four parallel, or rather slightly divergent, phyla, differing in the development of the horns, in the shape of the head and in the relative length and massiveness of the limbs. The teeth were all low-crowned, or brachyodont, the canines much too small to have been of any service as weapons and the incisors had curious little, button-shaped crowns, which can have had little or no functional importance, since they show hardly any wear, even in old animals. With such front teeth, a prehensile lip and long tongue would seem to have been neces- sary for gathering and taking in food. The {titanotheres were one of two perissodactyl families in which the premolars never became so large and complex as the molars. The upper molars had a longitudinal outer wall, Fia. 161.—Second upper molar, left side, of tTitanotherium. A., masticating surface; B., outer side of crown. composed of two deeply concave cusps, and two internal conical cusps, but no transverse ridges; the lower molars were composed of two crescents, one behind the other, a pattern which was very widely distributed among the early and primitive artiodactyls and perissodactyls. The so-called “horns” were not strictly such, but a pair HISTORY OF THE PERISSODACTYLA 311 of bony protuberances from the front of the skull and, from their shape, could hardly have been sheathed in horn. The long, immensely broad and massive head resembled that of some fantastic rhinoceros, as did also the body and limbs. The brain was quite absurdly small, the cavity for it, lost in the huge skull, would hardly contain the fist of an ordinary man; these great beasts must have been incredibly dull and stupid, surpassing even the modern rhinoceroses in this respect. As is generally true in mammals which have horns, antlers, Fic. 162. —Skull of + Titanotherium elatum. American Museum. or similar weapons borne upon the skull, or very large tusks, the bones of the brain-case were made enormously thick and yet lightened by an intricate system of communicating cavities or ‘‘sinuses,”’ separated by many bony braces and supports connecting the inner and outer denser layers, which form the surfaces of the bones. In this way the skull is made strong enough without any proportionate increase of weight to endure the severe shock of impact, when the horns or tusks are made use of. The principle is the same as the engineer employs in designing a steel truss-bridge. The upper profile of the head was deeply concave, just as it is in those rhinoceroses which are armed with nasal horns. 312 LAND MAMMALS IN THE WESTERN HEMISPHERE The neck was of moderate length and the body, as indicated by the long, arched ribs and the greatly expanded hip-bones, was extremely bulky and massive. The spines of the anterior dorsal vertebree were excessively long, forming a great hump at the withers. The limbs and feet were columnar, like those of an elephant; the feet were supported on a great pad, while the hoofs were mere excrescences on the periphery of the foot. The bones of the fore-arm were entirely separate and the ulna was very stout; in the lower leg also the bones were not codssified, but the fibula was but moderately heavy. This is a sharp contrast to the arrangement found in the horses and in those hoofed animals generally which are swift runners and have slender, elongate limbs and feet, such as deer, ante- lopes, camels, etc. Heavy, slow-moving animals, like elephants, tapirs, rhinoceroses, etc., almost always have separate fore- arm and leg-bones and generally a heavy ulna. The number of digits was four in the front foot and three in the hind. The genera differed in the proportions of limbs and feet, one having them longer and less ponderous than another, and, no doubt, the former was of swifter gait. At a certain level in the White River beds the ;titanotheres abruptly cease, disappearing with what seems like startling suddenness. In all probability, however, the extinction was more gradual and its apparent abruptness was due, partly at least, to the break in the deposition of the beds, which is very obvious. Such a break, or “‘unconformity,” as geologists call it, almost always implies an unrecorded lapse of time, which may have been very long. However it came about, gradually or suddenly, the extinction of these great animals is difficult to explain; no Carnivora of the time could have been formi- dable enemies and they had no rivals in their own walk of life. Their stupidity may have been a factor, but it seems more likely that the onset of some new infectious disease, perhaps imported by incoming migrants from the eastern hemisphere, gave the coup de grace. In the lower substage, beneath the HISTORY OF THE PERISSODACTYLA 313 unconformity, where the remains of {titanotheres are so abun- dant, successive changes may be observed. The species with great ‘‘horns,” rounded, flattened or triangular, are confined to the upper levels; in the middle section other species, some- what smaller and with shorter ‘‘horns,” are found, while in the bottom levels the animals are much smaller and have still smaller ‘‘horns.”’ The Uinta {titanotheres were much more numerous and varied than those of the White River; in the upper part of these beds are found two genera (tDiplacodon and +Protitan- othertum) which already had quite prominent bony protuber- ances on the nose; their canines were large enough to be of value as weapons and the incisors were well developed and functional. Evidently, there was a change here in the manner of feeding, the front teeth were used for cropping and browsing, a function which in the White River members of the family must have been largely taken over by the lips and tongue, while the growth of the horn-like protuberances on the skull rendered the canines superfluous as weapons. This latter change is one which recurs frequently in different phyla of the hoofed animals, in which the earlier and more primitive members had canine tusks, and the later, more advanced representatives developed horns, the tusks diminishing as the horns increased. While this rule is a general one, it is not entirely without exceptions. In the lower Uinta and in the Bridger the {titanotheres were extremely abundant and numerically they are the com- monest of all fossils in those beds; no less than five series or phyla may be distinguished, three of them being added in the upper Bridger. The differences between the phyla, however, principally concern the forms of the teeth and the shape of the skull; in some the head was short and broad, in others long and narrow, and in others again of medium proportions ; some had broad and extremely low-crowned grinding teeth, which in others were higher and more erect. But these are matters of minor detail, useful as they are in pointing the way 314 LAND MAMMALS IN THE WESTERN HEMISPHERE to a proper arrangement of the various species; in essentials, the forms all agreed and constituted several series of closely TR-BiVCe PloRsSFAL LH Fi Ay ae Fic. 163.— ¢ Titanothere ({ Mesatirhinus superior) with long, narrow head; Bridger stage. Restored from a skeleton in the American Museum. allied genera. Comparing these Bridger animals with the great j{titanotheres of the lower White River, the first and most obvious difference that strikes the observer is the very ‘much smaller size of the more ancient types. With some variation in this respect, hardly any of the Bridger species exceeded a modern tapir in stature and very much resembled one in proportions. The canine teeth were tusks pb as large as those of a bear and must have been Fic. 164.— Second very effective weapons; the molar-pattern was upper molar, right side of a Bridger identical with that found in the great Oligocene a beasts, but the premolars were simpler and relatively smaller. The skull had a straight upper profile, though in several of the phyla small bony protuberances were developed over RZ YY, y HISTORY OF THE PERISSODACTYLA 315 the eyes, and must clearly be regarded as incipient stages of the ‘‘horns”’ which were subsequently to become so long and prominent. Instead of being broad on top as it was in the White River genera, the cranium carried a high ridge of bone, the sagittal crest, which served for the attachment on each side of the great temporal muscle, one of the most important of the muscles of mastication. The trunk was less massive and the limbs were lighter than in the Oligocene genera, but the number of digits was the same, four in the front foot and three in the hind, and the hoofs were much better developed, serving actually to carry the weight and not being mere ex- crescences upon the periphery of a pad. Aside from the pro- boscis, which lends such a characteristic appearance to the existing tapirs, the {titanotheres of the Bridger must have looked much like tapirs, and in early days, when the mutual relationships had not been satisfactorily determined, they were frequently described as “‘tapiroid.”” The term is unobjection- able in so far as it is understood that a merely superficial like- ness is implied, not any real relationship other than that which unites all the perissodactyl families. As noted above, the phyla of the {titanotheres were much more numerous in the later than in the earlier part of the Bridger stage, when they were reduced to two. In the still older Wind River stage these two united into one. The Wind River animals ({Eotitanops) were similar, but much smaller, and occurred in incomparably less variety and abundance. Indeed, one of the most striking differences between the Wind River and the Bridger faunas consists in the great increase and diversification of the }titanotheres in the latter. There was, it is true, a second phylum of the family in the Wind River, represented by the genus tLambdotherium, but this was a short- lived series, which left no descendants in the Bridger or sub- sequent formations. These were the smallest known members of the family and were light, slender-limbed animals, a very notable difference from the others. 316 LAND MAMMALS IN THE WESTERN HEMISPHERE With the Wind River the history of the {titanotheres breaks off short, and from present information, can be carried no farther back. Possibly, there was a Wasatch ancestor, which only awaits discovery, but it seems more likely that these earliest known genera were belated immigrants from the same as yet unknown region, whence came the modernized and pro- gressive elements of the Wasatch fauna. Except for its ob- scure beginning, the family was pre-eminently characteristic of North America, and only two representatives of it have been found outside of that continent, one in Hungary and one in Bulgaria. No doubt others will yet be found in Asia. Both in its resemblances and its differences, as compared with the far longer and more complex story of the horses, the history of the {titanotheres has instructive bearings upon evolutionary theory. (1) Starting with two phyla, one of which speedily died out, the other ramified into four or five, which continued until the disastrous end, pursuing a nearly parallel course of develop- ment. (2) There was a great increase in size and especially in bulk and massiveness from species no bigger than a sheep in the Wind River stage to those which rivalled small elephants in the lower White River. (3) The teeth underwent comparatively little change; the incisors dwindled and lost functional importance and the ca- nines were reduced, horn-like growths taking their place as weapons; the premolars grew larger and more complicated, but never attained the full size and complexity of the molars, as they did in other perissodactyl families. (4) Horn-like, bony protuberances appeared first as small humps and knobs over the eyes and steadily enlarged, at the same time shifting their position forward, until they finally attained great size and were on the nose. (5) The skull was modified so as to support these weapons and endure the shock of impact when they were put to’ use, HISTORY OF THE PERISSODACTYLA 317 (a) by making the upper profile strongly concave from before backward ; (b) by greatly widening the top of the cranium, where in the older and more primitive genera the high and thin sagittal crest was placed ; (c) by immensely increas- ing the thickness of the cranial bones and at the same time hollowing them by means of an intricate system of Fic. 165.— Series of heads of + titanotheres in ascending geological order. A., ¢ Pal- ewosyops, lower Bridger. B., t Manteoceras, upper Bridger. C., t Diplacodon, Uinta. D., t Titanotherium, extreme development of horns, White River. From models in the American Museum and Princeton University. cavities ; in this way sufficient strength was secured without un- due increase in weight. (6) The growth of the brain did not keep pace with the increase in the size and weight of the body and head, and this deficiency may have been. a factor in determining the early extinction of the family. (7) To support the huge head, stout ligaments and power- ful muscles were needed in the neck and trunk and these in turn required large bony surfaces for their attachment. To meet this need, the spines of the anterior trunk-vertebre were 318 LAND MAMMALS IN THE WESTERN HEMISPHERE very much lengthened, so as to form a hump at the shoulders, and this elongation of the spines went on in proportion to the growing weight of the head. (8) The limb-bones increased in thickness until they be- came extremely massive, to carry the immense weight of the body, and they eventually lost the marrow-cavities, which were filled up with spongy bone, a great gain in strength. As is generally, though not universally, true of the large and heavy mammals, there was no coéssification between the limb-bones and no great increase in their proportionate length. The thigh-bone, or femur, lost the cylindrical shape of the shaft, becoming flattened and very broad, and acquiring something of the appearance of the same bone in the elephants. (9) There was no loss or codssification of elements in wrist (carpus) or ankle (tarsus) and no reduction of digits within the limits of the family. In the latest, largest and most special- ized genera, as well as in the earliest, smallest and most prim- itive, there were four toes in the front foot and three in the hind. We have the most cogent reasons for assuming that all mammals were derived from ancestors which had five toes in each foot, neither more nor less. If this be true, then the most Fia. 166.—Right manus of { titanotheres. A., t Titanotherium, White River (after Marsh). B., t Paleosyops, Bridger, Princeton University Museum. HISTORY OF THE PERISSODACTYLA 319 ancient known jtitanotheres, which were small and light, had already suffered the loss of the first digit in the fore foot and of the first and fifth digits in the hind foot, but there reduction ceased. With the growing body-weight, long, narrow and slen- der feet would have been a detriment, whereas in swift-running animals, like horses and deer, long and very slender feet are a great advantage. The contrast is both striking and instructive, showing the importance of a short, broad, polydactyl and pillar- like foot to very large and heavy mammals, all of which have feet of this character. (10) The hoofs, as shown by the terminal bones (ungual phalanges) which formed their bony cores, were reduced in size until they became mere nail-like excrescences around the border of the massive foot. 3,4. Tapiride and tLophiodontide. Tapirs and tLophiodonts The history of the tapir family is not at all satisfactorily known, partly because tapirs are comparatively rare as fossils in all of the Tertiary formations, and still more for the reason that the specimens so far collected are so fragmentary, not a single half-complete skeleton among them. Had these animals actually been as rare in North America as the fossils would seem to indicate, they could not possibly have maintained them- selves for so long a time, throughout nearly the whole of the Tertiary and Quaternary periods. For some reason, probably because they have always been forest-haunting animals, their _ habits must have kept them in places remote from the areas where the accumulation of sediments was in progress, and thus only occasional stragglers were buried and preserved. The rarity and incompleteness of the material render it impossible to give any such full account of the tapirs as is practicable for the horses and ftitanotheres, but the cir- cumstance is less unfortunate in the case of the tapirs than in that of many other families. This is because these creatures 320 LAND MAMMALS IN THE WESTERN HEMISPHERE have been so conservative and unprogressive, that they have undergone comparatively little change since their earliest re- corded appearance. They have been aptly termed “living fossils” and seem like belated survivors from some older world, out of place in the modern order of things. Attention has already been directed (p. 137) to the remarkable geographical distribution of the tapirs at the present time; Central and South America, southeastern Asia and the adjoining islands. Fic. 167.— American Tapir (Tapirus terrestris). By permission of W. 8S. Berridge, London. The tapirs are all of moderate size, going back to very small forms at the beginning of their history and never at any period developing into large animals. The only striking and un- usual feature about any of the existing members of the family is the long proboscis, a flexible, dependent snout, and, were they all extinct and nothing known of them but the skull, this proboscis could have been confidently predicated of them from the great shortening of the nasal bones. Small tusks, not showing when the mouth is closed, are formed in an ex- HISTORY OF THE PERISSODACTYLA 321 ceptional way by the enlarged external upper incisor and the lower canine, the upper canine being much reduced and without function. The grinding teeth have very low crowns, pre- molars (except the first) and molars are all alike and of a very simple pattern, which has been independently repeated in several different orders of herbivorous mammals; in both upper and lower teeth, there are two elevated, straight, trans- verse crests. Except for the modification of the skull which is conditioned by the development of the proboscis, the skeleton might be- long to any one of several Eocene or Oligocene fami- lies, and it is this general- ized, indifferent character which has led to the dub- bing of many early peris- sodactyls as ‘‘tapiroids.’’ The limbs are short and moderately heavy, the bones of the fore-arm and lower leg all separate and rye. 168, —Skull of American Tapir, right side. the number of toes is four in the front foot and three in the hind. The toes end in well- formed separate hoofs, but behind them is a pad, which carries most of the weight. The body is covered with smooth, short hair, which in the American species is ofa uniform dark brown, but in the Asiatic species the head, neck and limbs are black and the body is white. In both, however, the young have longitudi- nal, light-coloured stripes and spots on a dark ground (see Fig. 6, p. 47) indicating what the colour-pattern of the ancestral forms must have been. As might be inferred with certainty from the low-crowned teeth, the tapirs are browsing, not graz- ing, animals, feeding upon leaves and shoots and other soft vegetable tissues. They are shy and solitary in habit and live usually in thick forests and near water, which they frequently Y 322 LAND MAMMALS IN THE WESTERN HEMISPHERE enter, both for bathing and as a place of refuge when pur- sued. Under modern conditions, the only perissodactyls of the western hemisphere are the tapirs of the Neotropical re- gion, North America proper, which for ages was the principal home of the order, not having a single representative now. In the Pleistocene, tapirs were apparently more abundant than in any of the Tertiary epochs, but this was probably due to the fact that the Pleistocene of the forested regions is far more fully recorded than is any Tertiary stage. One species, which was hardly distinguishable from the Recent Central American form, was common in the forested region east of the Mississippi and in California, and a second species (Tapirus thaysii) was larger and heavier than the other. Except in Texas, none have been found in the Great Plains area, nor are they likely to be, for that region, then as now, appears to have been devoid of forests. No doubt, these Pleistocene species had substantially the same habits as the existing ones, but they were adapted to a colder climate and a different vegetation, for, except the Pinchaque Tapir (7'. roulini) of the high Andes, all the modern species are tropical in distribution. Concerning the Pliocene and Miocene tapirs, but meagre information has been obtained. Enough material has been gathered by the collectors to demonstrate the continuous pres- ence of the family in North America throughout those epochs, but the broken and fragmentary specimens are insufficient to show what the structural changes were. It should be remem- bered, however, that it is only in the region of the Great Plains and the Great Basin of Nevada that any considerable quantity of Miocene and Pliocene mammals have been found, and in those regions tapirs probably never were common. _ If the Peace Creek formation of Florida is properly classified as latest Pliocene, then at that time the American tapirs were essentially what they are to-day, for the Florida species is hardly separable from the modern T.. terrestris. Not till we reach the lower Oligocene, or White River beds, HISTORY OF THE PERISSODACTYLA 323 do we get material which permits the making of definite state- ments regarding the course of developmental changes. The White River genus, ¢ Protapirus, which is also found in the middle Oligocene of Europe, was a much smaller animal than any of the known Pleistocene or Recent species, barely more than half the size, in fact. The teeth show that the small Fig. 169. — Skull of White River tapir ({Protapirus validus), left side. Princeton Uni- versity Museum. N.B. This figure is much less reduced than Fig. 168. tusks were canines, both above and below, and that the curious substitution of the external upper incisor for the canine had not yet taken place. The grinding teeth were identical in pattern with those of the existing genus, but not all the premolars had yet acquired the form and size of the molars. In the skull the nasal bones had begun to shorten, but the change had not yet made much progress, and the proboscis must have been in merely an incipient stage of development. What little is known of the skeleton other than the skull was like that of the modern genus, but the bones were much smaller and propor- tionately lighter. The Eocene tapirs are still very imperfectly known; all that can be said of them is that they become successively smaller as they are traced backward in time, and that in them the premolar teeth were all smaller and simpler than the 324 LAND MAMMALS IN THE WESTERN HEMISPHERE molars. The Wasatch genus ({Systemodon) is the most ancient member of the series yet discovered. Dating from the Eocene immigration, the tapirs are to be regarded as a North American Fic. 170. — Head of the White River tapir ({ Protapirus validus). Restored from a skull in the museum of Princeton University. family, for there is here a complete continuity from the lower Eocene to the Pleistocene, while in Europe they first appeared, probably by migration from North America, in the middle Oligocene. In South America the history of the tapirs is even shorter and less eventful than that of the horses; the latter, as we have seen, reached the southern continent in the Pliocene and there gave rise to a number of peculiar and characteristic genera, but the tapirs have been found only in the Pleistocene of Argentina and Brazil and only the modern genus is repre- sented. Wofully broken and incomplete as the developmental his- tory of the tapirs still is, the fragments are nevertheless suffi- cient to show a mode of evolution differing in certain important HISTORY OF THE PERISSODACTYLA 325 respects from that followed by the horses or ftitanotheres. Certain features are common to all three groups, such as the in- crease in size and in proportionate stoutness from stage to stage Fic. 171. — Upper teeth, left side, of tapirs, showing comparative sizes. A, | Prota- pirus validus, White River Oligocene. B, Tapirus terrestris, modern. 13, external incisor. c, canine. m1, first molar. and the gradual enlargement and complication of the pre- molar teeth. On the other hand, the tapirs have been very conservative, and they underwent far less radical changes than did either of the other families. Aside from the pro- boscis and the modifications of the skull which the develop- ment of that organ necessitated, these animals remain to-day very nearly what they were in Oligocene times. This, then, ‘is an example of development practically restricted to a few organs, while all the other parts of the structure changed but little. The extinct flophiodonts, like the tapirs, of which they would seem to have been near relatives, are known only from incom- plete material, and comparatively little has been learned regard- ing their history. While they were abundant and varied in Europe, during the Eocene epoch, they never were a striking or prominent element among the mammals of North America, where they persisted one stage later, and they did not reach South America. In North America they are found from the Wasatch to the White River. 326 LAND MAMMALS IN THE WESTERN HEMISPHERE The White River genus (fColodon), which is fairly well known, might almost be described as combining the characters of horses and tapirs ; but such an expression is not to be inter- preted as meaning that this genus is in any sense a connecting link or transition between the two families, but merely that in certain important respects its course of development ran parallel with that followed by the horses. The teeth were very tapir-like, especially those of the lower jaw, which, indeed, are hardly distinguishable from those of a tapir, and the premolars had the molar-pattern. The limbs were very light and slender and the feet long and narrow; the fore foot retained a small fifth digit ; the feet, especially the hinder one, had a resemblance to those of the contemporary horses (}Meso- hippus), though the median digit was not so much enlarged, nor the lateral ones so far reduced. It is highly probable that, had this family persisted till the Pleistocene, instead of dying out in the lower Oligocene, it would have eventually terminated in monodactyl forms. The flophiodonts of the Eocene are represented by very fragmentary material; so far as that material goes, it does not show much change from the White River genus, except that the premolar teeth were smaller and simpler, the limbs and feet retaining the same characteristics of length and slender- ness. The Wasatch genus ({Heptodon) had a similar light- ness of limb and narrowness of feet, these characters thus ap- pearing at the very beginning of the family history, so far as their North American career is concerned. 5. Rhinocerotide. True Rhinoceroses The history of the great group of rhinoceroses and rhinoc- eros-like animals is a very long and complicated one, inferior in its completeness only to that of the horses. The com- plexity of the story arises from the large number of phyla into which the families are divisible, and, despite the great HISTORY OF THE PERISSODACTYLA 327 wealth of material and the admirable preservation of much of it, it is extremely difficult to find a clew through the mazes of this labyrinthine genealogy. From the standpoint of the existing geographical distribution of animals, few mammals could seem more foreign and exotic to North American life than do the rhinoceroses, and yet for a very long time that continent was one of the chief areas of their development, so far, at least, as that development can be followed. It is even probable, though not clearly demonstrable, that the family originated here and subsequently spread to the Old World, but not to South America, where no member of it has ever been found. The later history of the rhinoceroses ran its course in the Old World entirely, and the highest speciali- zations within the family are to be found there; in North America these animals are not known to have persisted beyond the lower Pliocene, and if they did survive, it was only as a few stragglers in out of the way places. The modern rhinoceroses are restricted to Africa, southern Asia and some of the larger Malay islands, Borneo, Sumatra and Java, and within these wide geographical limits are to be found the terminal representatives of at least three separate and quite distinct phyla, the African, Indian and Sumatran genera respectively (Opsiceros, Rhinoceros, Dicerorhinus). It will be advisable to begin the study of this peculiarly interesting family with a brief examination of its modern members, even though none of these are found in the western hemisphere. All the existing rhinoceroses are large and massive animals, ranging from four feet to six feet six inches in height at the shoulder, and all have solid dermal horns, except in most females of the Javan species! (R. sondaicus). The Indian and Javan species have a single horn on the nose, while those of Africa and Sumatra have, in addition to the nasal horn, a second one on the forehead. The horns, thus, do not form a 1 The names, Javan and Sumatran rhinoceroses, are somewhat misleading, since both of these species are also found on the mainland of India. 328 LAND MAMMALS IN THE WESTERN HEMISPHERE transverse pair, but are placed in the median line of the head, one behind the other; it should also be noted that these horns are solid, dermal structures, made up of agglutinated fibres or hairs and not having a bony core formed by outgrowths of 7 so Fic. 172. —Skull of the Javan Rhinoceros (R. sondaicus). Note the single upper inci- sor, and the rough surface on the nasal bones for the attachment of the single horn. the skull, as do the horns of most ruminants, such as oxen, sheep and antelopes, which are therefore called ‘‘hollow- horned”’ (Cavicornia). The skull, however, betrays the pres- ence of horns by the extremely rough areas which serve for their attachment and thus the presence or absence of these weapons may be readily determined in the case of an extinct species of which only the skeleton remains. The skin is very thick and coarse, typically ‘‘pachydermatous,” and is quite naked in most of the species ; but in the Sumatran form there is a sparse coat of hair, which is quite thick in the young animal. In the Indian Rhinoceros unicornis the enormously thick skin has conspicuous and regularly arranged folds, which make the creature look as though encased in armour ; the ears and tail are tufted with hair. In the African and Sumatran genera the folds are obscurely marked and not definitely arranged, giving the body a smoother appearance. All the existing species, except one, are browsers and feed upon leaves HISTORY OF THE PERISSODACTYLA 329 and twigs, and they frequent forests and marshes where their food is abundant. Not that these and other browsing animals do not occasionally eat grass, but it is not their principal diet. The exception noted is the largest of all the living species, the Broad-Lipped Rhinoceros (erroneously called ‘‘White’”’) of Africa, Opsiceros simus, which is strictly a grazing animal and therefore frequents more open country than the other African species, O. bicornis. There are considerable differences in proportions and general appearance among the various species, but they all have short necks, very long and massive bodies, short and heavy limbs and short, columnar feet, which look much like those of elephants, but have only three toes each. In all but two of the living species the upper lip is prehensile and characteristi- cally pointed and can be used to pick up very small objects, like the ‘‘finger”’ on an elephant’s trunk; in the Sumatran species (Dicerorhinus sumatrensis) the lip, though pointed, is horny and inflexible, while in the African O. simus it is broad and straight-edged. The teeth of the modern rhinoceroses are extremely char- acteristic and may always be recognized at a glance. In the African genus (Opsiceros) there are no front teeth, all the incisors and canines being lost; the other genera have on each side a single large and trenchant upper incisor, in shape like a broad, obliquely edged chisel, which shears against a still larger elongate and tusk-like lower incisor, that is procumbent and points directly forward. The Indian Rhinoceros (R. unicornis) is said to use its tusks as weapons in very much the same fashion as the Wild Boar. Between the large lower tusks there is a pair of very small incisors, which can have little or no functional value ; the third lower incisor has been suppressed, as have also the canines of both jaws. The dental formula then is: 74 or ¢, ct, pt, m%,x2=28 or 34 (see p. 93). The premolars, except the first, though somewhat smaller than the molars, have essentially the same pattern. The upper molars have 330 LAND MAMMALS IN THE WESTERN HEMISPHERE moderately high crowns, yet they are purely brachyodont, except in the grazing, broad-lipped African species (O. simus), in which they may fairly be called hypsodont. The external wall of the tooth is broad and nearly smooth, not divided into cusps, as it is in the horses and tapirs, and the two transverse crests, which in the tapirs are directly transverse, are very oblique. In all the existing species additional complications are given by the short spurs, which project inward from the outer wall or from the transverse crests. The lower molars are formed each of two crescents, one behind the other, but their arms or horns are angulate, not curved as they are in other perissodactyls which have crescentic lower teeth. The upper surface of the skull is very concave in the antero- posterior direction and very broad over the cranium, where there is no sagittal crest. The nasal bones are immensely thick and strongly arched, with the convexity upward; both this arching of the nasals and the fore-and-aft concavity of the skull are devices for giving a strong and solid attachment to the great nasal horn, for the attachment of which these bones have an extremely rough surface, and in the two-horned species, a second roughened area on the forehead marks the place of attachment of the frontal horn. The bones of the cranium are very thick, but lightened by the many chambers which traverse them. The articulation of the lower jaw with the skull is in some respects unique among mammals; the post- ‘ glenoid process is a long spike, which fits inside of a bony lump (the postcotyloid process) behind the condyle of the lower jaw, and the posterior margin of the latter is greatly thickened. The neck is short and stout, the trunk very long, broad and deep, the long and strongly arched ribs and the widely ex- panded hip-bones providing space for the great mass of viscera. The bones of the limbs are short and very massive ; the humerus has a very prominent deltoid ridge and the femur an unusually large third trochanter; the bones of the fore-arm and lower leg are separate, as in the massive ungulates generally. The HISTORY OF THE PERISSODACTYLA 331 foot-bones are likewise extremely short and heavy, and the number of digits is three in each foot. Each of the five or more existing species has its skeletal pecu- liarities, every portion of the bony structure showing characteristic features; but these are only minor modifications of the general plan and may be neglected in any compre- hensive account of the living representa- tives of the family. In order to find any American members of this family, it is necessary to go back to the lower Pliocene, where a great abun- dance of them is encountered, representing, according to Osborn’s view, four or five phyla; and just as in the case of the horses of the same formation, they were Fi¢. 173.— Left manus ‘ of Indian Rhinoceros an assemblage curiously made up of pro- @p. unicornis). gressive and old-fashioned, conservative . genera, — some were persistent native stocks, others the de- scendants of immigrants from the Old World, which reached America in the middle Miocene. There was great variety of form, size and proportions among these animals, North America at that time having a larger number of genera and species than Africa and Asia combined have now. Some were quite small, some large, though none equalled the larger modern species. Some of the genera had relatively long legs, but in one genus, | Teleoceras (Fig. 125, p. 230), an Old World type, they were most grotesquely short, the belly almost touching the ground, as in a hippopotamus. Most of these rhinoceroses were hornless, but +Teleoceras had a small horn on the very tip of the nose. In consequence of the lack of horns, the nasal bones were thin and weak, in marked contrast to the massive, convex nasals of the modern species, and, for the same reason, the upper profile of the skull was nearly straight. Except for minor details, the dentition was in very nearly the modern stage 332 LAND MAMMALS IN THE WESTERN HEMISPHERE of development; there was a single trenchant upper incisor on each side, a procumbent lower tusk and between the tusks a pair of small incisors; the other incisors and the canines were already lost. One genus (tPeraceras) had lost all the upper front teeth. The grinding teeth had the same character as in the existing species, but were somewhat simpler, owing to less development of the accessory spurs. In the more pro- gressive types the teeth were rather high-crowned, though in none were they actually hypsodont; while the persistent ancient genera had teeth with much lower crowns. Aside from the differences in the skull, which are obviously to be correlated with the absence or very small size of the horn, the skeleton in these Pliocene genera differed but little from the type common to the existing rhinoceroses, and in all the species the feet were three-toed. In short, the denti- tion and skeleton, except the skull, had already attained to substantially the modern conditions. While the Old World at that time had both horned and hornless rhinoceroses in abun- dance, none of the genera with large and fully developed horns ever migrated to the western hemisphere. This is the more remarkable in that the great tWoolly Rhinoceros (Opsiceros tantiquitatis) of the Pleistocene, which had two very large horns, inhabited Siberia with the {Mammoth (Elephas {prim- genius). The latter-extended its range through Alaska and the northern United States, but the rhinoceros, for some unknown reason, did not accompany it in its eastward wanderings. The rhinoceroses of the upper Miocene did not differ suffi- ciently from those of the lower Pliocene to call for particular attention. Needless to say, there were differences between the species of the two epochs, but in such a sketch as this only the broader and more obvious changes can be taken into account. Even in the middle Miocene the only feature which calls for notice was the first appearance in North America of the Old World genus }Teleoceras, which became so abundant in the HISTORY OF THE PERISSODACTYLA 333 upper Miocene and lower Pliocene. The middle Miocene species (t7’. medicornutus) would seem to have been descended from {T7. aurelianensis of the lower Miocene of France; the two species agreed not only in having a small horn on the tip of the nose, but also in the presence of a still smaller one on the forehead. In the lower Miocene but two phyla of rhinoceroses have been found, both of which were the comparatively little changed descendantsof Oligocene ancestors ; and there was thus a notable difference from the rhinoceroses of the middle Miocene and sub- sequent stages, which were decidedly more modern in character. One of these phyla was constituted by those rhinoceroses (tDiceratherium, Fig. 129, p.239) whichhad a transversely placed pair of horns on the nose, not one behind the other, as in all of the subsequent two-horned species, of which North America had .but the one middle Miocene form ({T7. medicornutus) mentioned above. The lower Miocene ‘species of tDicera- thertum was a very small animal, and smaller than any mem- ber of the family from later formations. The tdiceratheres originated in North America, and the stages of their develop- ment may be clearly made out; they also migrated to the east- ern hemisphere and have been found in France, though it is possible that the genus was not truly monophyletic and arose independently in both hemispheres. The second phylum is that of the hornless forms (tCenopus) which were so abundantly represented in the Oligocene and persisted with little change into the Pliocene. In the upper Oligocene, or John Day, the fdiceratheres are the only rhinoceroses certainly yet obtained, and of these there were several species, large and small. The hornless forms may have been present in Oregon, but this has not been clearly demonstrated. That they continued to exist some- where during that stage is hardly open to question, for they reappeared in the lower Miocene. From the White River, or lower Oligocene, many well- a 2 334 LAND MAMMALS IN THE WESTERN HEMISPHERE preserved rhinoceroses, including complete skeletons, have been gathered in the various collections and display very interesting differences in the three substages of the White River beds. In the uppermost substage is found the apparent beginning of the jdicerathere phylum, though it may be traced back to the middle substage; the nasal bones had become much thickened so as to serve as a support for the horns, and these are indicated by a small, but very rough, area on the outer side of each nasal. Comparing this White River species with those of the upper Oligocene and lower Miocene, two dif- ferences may be observed: in the later species the horn- supports were well defined bony knobs or prominences, and these knobs were close to the anterior ends of the nasals ; while in the White River animal the places for the attachment of the horns were mere roughened areas, and these were well behind the tips of the nasals. This is not an infrequent sort of change, that horns should shift their position forward or that the portion of the nasals in front of the horns should be shortened. Parallel changes occurred among the ftitan- otheres. : In the middle White River all the rhinoceroses were horn- less, but the same two phyla may be distinguished ; the actual starting point of the fdiceratheres had no indication of the nasal horns, but may be identified as such by their close resemblance in other respects to the species of the upper substage in which the incipient horns appeared. Much commoner were the mem- bers of the typical hornless line (see Fig. 135, p. 256), which, though true and unmistakable rhinoceroses, were yet far re- moved in many details of structure from the progressive genera of the middle and upper Miocene. There are several species in this phylum, which constitute a series of diminishing size al- most in proportion to their increasing antiquity. The dentition was already thoroughly and characteristically rhinoceros-like, but a more primitive feature was the presence of a second upper incisor, a small tooth placed behind the trenchant one, HISTORY OF THE PERISSODACTYLA 335 making the incisor formula }; the third incisor and the canines of both jaws were already lost. The assumption of the molar- ee Fic. 174. —Skull of thornless rhinoceros (t Cenopus tridactylus) ; middle White River stage. (After Osborn.) pattern by the premolars varied much in degree of complete- _ hess in the different species; the upper molars, while having all | the essentials of the rhinocerotic-plan of struc- \ ture, had a much less complex appearance \ than in the Recent genera, because of the ab- ‘sence of the accessory spurs; and all the grinding teeth were very low-crowned, in strong contrast to the high-crowned (yet not properly hypsodont) teeth of the middle Mio- Eonar cene and subsequent genera. of t Cenopus, show- As already mentioned, there was much metho nERSHCBUE variation in size among the species, but none was as large as those of the Miocene and Pliocene genera, not to mention the enormous animals of the Pleis- tocene and Recent epochs in the Old World. The com- moner species of the middle White River substage (tCeno- pus occidentalis) was an animal nearly equalling in size the American Tapir (7. terrestris) and quite like that species in 336 LAND MAMMALS IN THE WESTERN HEMISPHERE its proportions, the limbs being relatively longer and less heavy and the feet narrower than in the rhinoceroses of the subse- quent geological epochs. The skull, being hornless, had thin, pointed and nearly flat nasal bones, an almost straight and horizontal upper profile, and a short and low, but distinct, sagittal crest; the cranial bones were quite thin, there being no extensive development of sinuses within them: The artic- ulation of the lower jaw with the skull was only beginning to take on the characteristic peculiarities seen in the later genera, and the hinder margin of the lower jaw was not much thickened. Thus, many of the features which distinguish the skull in all Recent and Pleistocene and most Pliocene, and upper and mid- dle Miocene rhinoceroses were entirely lacking in tCenopus, yet no anatomist could doubt that the White River animal was a genuine rhinoceros. The neck was short, but not very heavy, the trunk elongate, but not massive, the ribs not being inordinately long nor strongly arched, and the hip-bones so little expanded that they were tapiroid rather than rhinocerotic in appearance. The limb-bones were relatively much more slender than in any existing species, and, although every one of them was char- acteristically that of a rhinoceros, yet the comparative light- ness of body and slenderness of limb gave to these bones a cer- tain resemblance to those of tapirs. The feet, which were moderately elongate and rather narrow, were three-toed, as in all subsequent North American species and in all existing members of the family. The most ancient and primitive representative of the true rhinoceroses so far discovered occurs in the lowest division of the White River beds and is of particular interest as throwing light upon the origin of the family. The genus (t7'rigonias) differed from that (tCenopus) which was so abundant in the middle White River substage in several highly significant particulars, though on a merely casual inspection one might easily be misled into thinking that the two animals were nearly Zz s HISTORY OF THE PERISSODACTYLA 337 identical, for ¢Trigonias was an undoubted rhinoceros. Such an identification, however, would be a great mistake, for the Fie. 176. —Skull of t Trigonias osborni, lower White River. (After Hatcher.) differences, though not striking, are very important. In the upper jaw the first or anterior incisor had already assumed the characteristic trenchant, chisel-like shape, but two other incisors were present also, thus bringing the number up to the original three, common to all early perissodactyls; even more interesting is the presence of a small upper canine. The lower jaw likewise had three incisors on each side, the first and third small, the second en- larged and tusk-like, but the canine had already been suppressed, and thus the dental formula Fic. 177. — Anterior end of right upper jaw ot was: i8, ci, Pi; ms 4 2S t Trigonias osborni (after Lucas). Cy canine. 42, or 14 more than the i a os incisor. «2, middle incisor. 71, formula of the existing African species. The premolars were smaller and less complex than the molars. From this ancient genus may readily be inferred the steps Zz 338 LAND MAMMALS IN THE WESTERN HEMISPHERE by which the peculiar characters of the anterior teeth in the true rhinoceroses were attained. The first stage was undoubt- edly an animal in which, as in all other Eocene peris- sodactyls, there were three well-de- veloped incisors on each side of both jaws, 12 in all, and moderately promi- nent canine tusks; all these teeth were erect. The second stage was the en- largement of .the first upper and sec- Fig, 178. inter end of left upper jaw of tCenopus,A, ond lower incisors adult; B, immature animal (after Osborn). JI1, first 7 i incisor; I 2, second incisor; C, canine. the latter becoming less erect and begin- ning to assume the recumbent position; at the same time the other incisors and the canines were reduced in size and were so little. used that they lost their functional importance. The third stage, in which the first and second lower incisors were horizontal and pointed directly forward, and the first upper and -second lower teeth were still further enlarged, the non-func- tional teeth reduced in size and the lower canine suppressed, was realized in the genus {7rigonias. There were thus but two hypothetical stages between this lower White Region genus and the tapir-like forms of the middle Eocene, so far, at least, as the anterior teeth are concerned. The skeleton of {Trigonias was, on the whole, very much like that of the succeeding genus, t{Cenopus, of the middle substage of the White River, but with the important exception that the front foot had four digits instead of three. The HISTORY OF THE PERISSODACTYLA 339 pollex, or first of the original five, almost always the first to disappear, had been suppressed, the third or median digit was already the largest of the series, both in length and breadth ; the second and fourth, some- what shorter together made a symmetrical pair, while the fifth, though much the most slender of all, was still func- tional and had retained all of its parts. In the hind foot the digits had been reduced to three. This arrangement, four toes in the manus and three in the pes, is the same as is found in the existing tapirs and in the Eocene perissodac- tyls generally, with only two or three known exceptions. In the Oligocene, on the other hand, all the genera except the {titanotheres, tapirs, tlophiodonts and famynodonts were tri- dactyl both before and behind. With tTrigonias the definitely known history of the true rhinoceroses breaks off abruptly, and it is possible that that genus was an immigrant, though it is perhaps more likely that its ancestors existed in the upper and middle Eocene (Uinta and Bridger stages) of North America. Some fragmentary specimens from the Uinta beds, too imperfect for any definitive identification, are an encouragement to hope that the fore- runner and direct ancestor of +Trigonias may yet be dis- covered in that formation. It is also quite possible that one of the larger species of the genus tHyrachyus, so abundant in the Bridger and going back to the Wind River, may take its place in the same series. Fig. 179.— Left manus of { Trigonias os- borni. (After Hatcher.) 340 LAND MAMMALS IN THE WESTERN HEMISPHERE 6. {Hyracodontide. {Cursorial and +Aquatic Rhinoceroses The luxuriant diversification of the rhinoceros-stem was not exhausted by the many phyla of what we have called the true rhinoceroses. Two other series, very distinctly marked and rather distantly connected with the first, are yet to be considered. These two series, the thyracodonts (in the narrow sense) and the famynodonts, ran courses which, in certain respects, were singularly alike; both were of North American origin and one, the fhyracodonts, was entirely confined to that continent, while the other sent out late migrants, which entered Europe, no doubt through Asia, and both ended their careers before the close of the White River time. Their history was thus a brief one when compared with that of the true rhinoceroses, three phyla of which persist to the present day, though their geographical range is greatly restricted in com- parison with what it was in the Miocene and Pliocene, when they ranged over every continent except Australia and South America. Just how to classify these three series of rhinoceroses and rhinoceros-like animals, so as most accurately to express their mutual relationships, is a question that has received several answers. One method suggested is to include them all in a single family and to make a subfamily for each of the three well-distinguished series; this is the arrangement which personally I should prefer. A second plan is to accord family rank to each of the three groups; while the most elaborate scheme, that of Professor Osborn, is as follows: for the rhi- noceroses, in the broader sense, he makes two families, the Rhinocerotide and the tHyracodontide, and divides the former into four subfamilies, which include all of the true rhinoceroses, living and extinct, of the Old and New Worlds, and the latter into two subfamilies, the t{Hyracodontine and tAmynodontine. It is not a matter of very great moment as to which of these three schemes is followed, and I shall therefore adopt the one HISTORY OF THE PERISSODACTYLA 341 proposed by Professor Osborn, in order to avoid, so far as possible, the confusing effect of different methods of classi- fication. As before mentioned, the subfamily of the thyracodonts (tHyracodontine) became extinct in White River times, during Fig. 180.— ¢ Cursorial rhinoceros (+ Hyracodon nebrascensis), White River stage. Re- stored from a skeleton in the Museum of Princeton University. most of which it was represented by the single genus + Hyra- codon, whence are derived the names for the family and sub- family. The series was purely North American, and no mem- ber of it has ever been found in any other continent. The species of tHyracodon were altogether different in appearance and proportions from the true rhinoceroses, being lightly built, slender, cursorial creatures, suggestive rather of horses than of rhinoceroses, to which they bore much the same rela- tion as the slender-limbed, narrow-footed tlophiodonts did to the tapirs (see p. 326); in size, they were somewhat taller and considerably heavier than a sheep. The low-crowned grinding teeth had the unmistakable rhinoceros-pattern, and between them and the teeth of the 342 LAND MAMMALS IN THE WESTERN HEMISPHERE contemporary {Cenopus the difference was merely one of size, except for one small, but not insignificant feature. The last upper molar had not perfectly acquired the triangular form characteristic of all the true rhinoceroses, caused by the complete fusion of the outer wall with the posterior crest, but the wall projected a little behind the crest, as in perissodactyls generally. Premolars (except the first) and molars were alike in structure and of nearly the same size. While the grinding teeth were thus hardly to be distinguished from those of the true rhinoceroses, the anterior teeth, incisors and canines, were totally different; they were very small and had simple, pointed and slightly recurved crowns, and were all very much alike in size and form. Thus, there were in the front of the mouth eight small, hook-like teeth, above and below, which were obviously quite useless as weapons; and as the skull had no horn,.the animal was defenceless, and must have de- pended entirely upon “speed for its safety from the attacks of the larger and more powerful beasts of prey. ; The skull was short, deep and thick, and the head must have been heavy and clumsy, quite out of keeping with the body and limbs. The neck was surprisingly long, longer in- deed proportionately than in the contemporary genus of horses ({Mesohippus), but the neck-vertebre were relatively stout and strong, as was required for the muscles to move and control the heavy head. The body was rather elongate, but not deep or massive, and the limbs were proportionately much longer than in any of the known rhinoceroses. The limb-bones, one and all, despite their length and slenderness, bore an unques- tionable likeness to those of the true rhinoceroses. In this elongation of the limbs the fore-arm and thigh were the parts most affected, and the slenderness, though in notable contrast to the proportions both of the true rhinoceroses and the tamyno- donts, was yet much less marked than in the middle Eocene representatives of the thyracodonts themselves. The feet were long and narrow, approximating, though not actually HISTORY OF THE PERISSODACTYLA 343 attaining the proportions of the feet in the White River horses (t{Mesohippus). There were three digits in each foot, and the median toe (third of the original five) was so much enlarged and the lateral toes (second and fourth) so reduced, though still functional, as strongly to suggest a monodactyl foot as the outcome of this course of development, had not the early extinction of the subfamily put an end to it. It is interesting to reflect that, had the flophiodonts and fthyracodonts con- tinued their existence to the present time and had persisted in advancing along their particular lines of specialization, we should, in all probability, have had monodactyl tapirs and rhinoceroses, as well as horses. As in the case of so many other mammalian series, the thyracodonts of the but partially explored Uinta formation are still very imper- fectly known. Al- most all that can be positively stated about them is that they were smaller than their White River successors and that the assumption of the molar-pattern by the premolars was incomplete. In the upper Bridger beds also not very much is known regarding the then representa- tives of the series, Fic. 181.— Left manus of } cursorial rhinoceroses.