CHAPTER VII

THE SUCCESSIVE MAMMALIAN FAUNAS OF NORTH AND SOUTH AMERICA

The 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 drawback 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 animals 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. Attention was long ago directed to the fact that the tops of high mountains support a flora and fauna which, on the lowlands, 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 Pleistocene 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 “discontinuous distribution” (see p. 138) 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 attained by European geologists and palæontologists.” According 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 reëstablishment of glacial conditions on a grand scale. Regarding 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 Pleistocene 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 advantage 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 concerning 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 mammals 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 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.

[Illustration: FIG. 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 †columbi_). 2. Giant †Ground-Sloth (_†Megalonyx jeffersoni_). 3. †Stag-Moose (_†Cervalces scotti_). 4. †American Mastodon (_†Mastodon americanus_). 5. †Giant Beaver (_†Castoroides ohioensis_). 6. †Texas Horse (_Equus †scotti_). 7. †Sabre-tooth Tiger (_†Smilodon californicus_).]

Most surprising, perhaps, in a North American landscape, is the presence of the Proboscidea, of which two very distinct kinds, the †mastodons and the true elephants, are found together. Over nearly the whole of the United States and southern Canada, and even with sporadic occurrence in Alaska, ranged the †American 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 †Mastodon, 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 externally; this is a 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 †Mammoth (_Elephas †primigenius_), a late immigrant from 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 contents of the stomach and the partially masticated food found in the mouth show that the animal fed upon the same vegetation 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 (_E. 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 Palæolithic 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 †Columbian Elephant (_E. †columbi_) 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 somewhat 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 and even throughout the table-land of Mexico. The areas of the two species overlapped along the northernmost United States, but are elsewhere distinct.

[Illustration: FIG. 114.—Restoration of the †Columbian Elephant (_Elephas †columbi_) from a skeleton in the American Museum of Natural History.]

A third species was the huge †Imperial Elephant (_E. †imperator_), the largest of American forms, to which Osborn’s calculations 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 Pleistocene 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 Nebraska 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.

[Illustration: FIG. 115.—A Horse (_Equus †scotti_) from the older Pleistocene of Texas. Restored from a skeleton in the American Museum of Natural History.]

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 (_E. caballus_), to which all the domestic breeds are referred, is not represented. The smallest known member of the genus is the pygmy _E. †tau_ of Mexico. _E. †fraternus_, likewise a very small species, is found especially in the southeast, but extended as far north as Pennsylvania and west to Nebraska. On the other hand, _E. †giganteus_ of Texas exceeded the heaviest modern draught-horses in size and was the largest of the American species; of other Texan forms, one (_E. †scotti_) resembled Burchell’s Zebra (_E. burchelli_) in the proportions of head and neck, body and limbs, while another (_E. †semiplicatus_) was more ass-like. The forest horse of the eastern states has been named _E. †pectinatus_, 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. †complicatus_, a horse of about 14½ 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. †occidentalis_, equalling _E. †complicatus_ in size, but with much more simple teeth, and associated with it the much larger _E. †pacificus_, which was inferior only to _E. †giganteus_ 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 Pleistocene 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 continent 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, _Tapirus †haysii_, and a smaller one which seems to be identical with the living _T. 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 by two genera, now extinct, one of which (_†Platygonus_) had crested grinding teeth and much longer legs than the modern peccaries. Another indigenous group, strange as 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 (_Odocoileus_) 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 comparatively 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 Maryland 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 _†Euceratherium_) 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 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 than _B. bison_, and some were gigantic, such as _B. †latifrons_, which had a spread of horns of 6 feet and is found through the Mississippi Valley, and _B. †crassicornis_ of Alaska.

[Illustration: FIG. 116.—Restoration of _†Preptoceras_, a musk-ox like animal from the Californian Pleistocene. (From a skeleton in the museum of the University of California.)]

Preying upon this great assemblage of hoofed animals was a corresponding array of Carnivora, most of which were indigenous 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 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 †sabre-tooth tigers (_†Smilodon_, 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 unknown. In addition to the pumas and lynxes, there were some very large true felines (_Felis †atrox_ and _F. †imperialis_), 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 †dirus_ (also called _C. †indianensis_) so abundant in the asphalts of southern California. Bears were not so common 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 originated. Their absence from the older Pleistocene (Equus Beds) may be accounted for by the fact that those beds contain 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 †short-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 (_Hydrochærus capybara_), the largest of existing rodents, failed to gain a permanent foothold, but another South American form, the Short-tailed or Canada Porcupine (_Erethizon 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 (_†Castoroides_), one species of which, _†C. 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 _†Castoroides_ was simply a gigantic beaver, but the grinding teeth were remarkably like those of the South American Capybara (_Hydrochærus_), so much so that it has been mistakenly referred 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 †ground-sloths, and the _†Glyptodontia_, which might well be called giant armadillos, if that name were not already in use for a living Brazilian animal. Both suborders are completely extinct, but they long played a very conspicuous rôle in South America, where they originated and whence the North American representatives migrated. The †ground-sloths were great, unwieldy, herbivorous animals covered with long hair, and in one family (†Mylodontidæ) 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 _†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 _†Megalonyx_, being no doubt better adapted to subsisting upon the vegetation of the plains and less dependent upon trees for food.

The †Glyptodonts were undoubtedly present in the North American Pleistocene, but the remains which have been collected so far are very fragmentary and quite insufficient to give us a definite conception of the number 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 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 cold of oncoming 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. It is 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 (_†Mastodon americanus_, see p. 196) was still abundant in the forested regions and was apparently able to withstand severe winter temperatures, as certainly was the †Mammoth (_Elephas †primigenius_, see p. 196), which was so abundant in the coldest part of Siberia and which extended south to the Potomac, presumably at this 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 intermediate 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 prehensile 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.

[Illustration: FIG. 117.—_†Cervalces scotti_: restored from a skeleton in the museum of Princeton University.]

Even more typically northern than the Caribou were the Musk-Oxen, of which two genera occurred in the late Pleistocene. One of these, _†Symbos_, is extinct and was characterized by its short horns; the other, _Ovibos_, is the genus to which the existing species, _O. moschatus_ and _O. wardi_, belong and is now confined 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 †sabre-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 Pennsylvania, 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 †sabre-tooth tigers, the gigantic †short-faced bears, the tapirs and many varieties of 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 †mastodons, the †giant beavers and South American water-hogs, the huge †ground-sloths and †glyptodonts, have all disappeared, leaving a continent, that, by contrast, is “zoölogically 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 Argentina a wonderful museum of Pleistocene mammals, such as occurs nowhere else in the known world, and this is supplemented 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 successive 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 belonged all of the Carnivora, which therefore resembled their North American relatives, but were less varied in character. Of the bears, only the huge, †short-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 †sabre-tooth tigers (_†Smilodon_) were as common in 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 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 genus (_Cyon_) as the Dhole of India. The weasel family (Mustelidæ) were less numerous and varied than in the northern continent, as they still are; coatis (_Nasua_) and raccoons (_Procyon_) were abundant and one species of the latter was much larger than any existing one; extinct species of skunk (_Conepatus_), tayra (_Tayra_) and otter (_Lutra_) were also present, but the badgers, minks, martens and wolverenes were not.

[Illustration: FIG. 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. _†Dœdicurus clavicaudatus._ 2. _†Glyptodon clavipes_, †glyptodonts. 3. _†Macrauchenia patachonica_, one of the †Litopterna. 4. †Pampas Horse (_†Hippidion neogæum_). 5. _†Toxodon burmeisteri_, a †toxodont. 6. _†Megatherium americanum_. 7. _†Mylodon robustus_, †ground-sloths.]

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 common 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 (_E. 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 _†Hippidion_. 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 comparatively 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 _†Hyperhippidium_, 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.

[Illustration: FIG. 119.—A Pampas Horse (_†Hippidion neogæum_). Restored from a skeleton in the National Museum, Buenos Aires.]

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 in the southern continent now. Several species of †mastodons have been found in Brazil, Argentina, Bolivia and elsewhere, but none of the true elephants. Why the †mastodons were able to make their way into South America, while the elephants were not, is one of the puzzling questions of mammalian distribution to which no answer can be given.

All the preceding types of hoofed animals, the horses, tapirs, peccaries, llamas, deer, antelopes and †mastodons 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 †mastodons 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 outside 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 rôle 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 †Typotheria, which some authorities regard as a suborder, while others assign to it a full ordinal rank.

[Illustration: FIG. 120.—A Pampean †Litoptern (_†Macrauchenia patachonica_). Restored from a skeleton in the Museum of La Plata.]

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 _†Toxodon_, type of the order †Toxodontia, a ponderous 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, but the structure of its teeth, as Mr. Owen states, proves indisputably that it was intimately related to the Gnawers [_i.e._ Rodentia] ... in many details it is allied to the Pachydermata: 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.”[4] Modern views concerning the relationships of _†Toxodon_ are very different from those advanced by Darwin, but he gives a vivid picture of its diverse likenesses. Neither _†Macrauchenia_, _†Typotherium_ nor _†Toxodon_ has been found in the Brazilian caverns, but this is no doubt due to the accidents of preservation, for the latter animal ranged north to Nicaragua.

[Illustration: FIG. 121.—A Pampean †Toxodont (_†Toxodon burmeisteri_). Restored from a skeleton in the La Plata Museum.]

The rodents likewise were partially of immigrant and partially of native stock. To the former belonged the few mice and rats and a meadow-mouse (_Microtus_), a group not represented 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 existing genera; the tree-porcupines, cavies, agoutis, spiny-rats, vizcachas, 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, _†Protopithecus_, 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 Edentata, 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 _†Chlamydotherium_, which was a huge creature almost as large as a rhinoceros. Then there were the two extinct suborders of the †glyptodonts (†Glyptodontia) and the †ground-sloths (†Gravigrada) 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 †glyptodonts have ever been found; the short, deep head, with its shield 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 †glyptodonts 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 _†Sclerocalyptus_ the hinder half of the sheath coalesced into a single piece, marked only by the elaborate ornamentation of the horny scales, while in _†Dœdicurus_ the end had a tremendous, club-like expansion, which must have been set with great horn-like spines. The †glyptodonts 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 alligator 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 †ground-sloths, and though these ranged far more widely through the northern continent than did the †glyptodonts, 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 †ground-sloths which occur in the North American Pleistocene, _†Megatherium_ and _†Mylodon_, are also found in South America; and though _†Megalonyx_ has not yet been obtained there, the family of which it is a member was represented. 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.

[Illustration: FIG. 122.—A gigantic Pampean †Ground-Sloth (_†Megatherium americanum_). Restored from a skeleton in the Museum of La Plata.]

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 †ground-sloths and †glyptodonts, the †litopterns, †toxodonts and †typotheres, the antelopes, horses and †mastodons have all disappeared from the continent, or vanished altogether from the face of the earth.

II. 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 northwestern Texas, which have yielded but a scanty list of mostly ill-preserved fossils. Obviously, these give us a very incomplete picture of the life of that time. The great †ground-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 †glyptodonts were likewise represented by one genus (_†Glyptotherium_) 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 †mastodons, 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 elephantine 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 widespread 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.

[Illustration: FIG. 123.—†Horned Gopher (_†Epigaulus hatcheri_), lower Pliocene, Nebraska. Restored from a skeleton in the U.S. National Museum.]

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 †Giant Beaver, marmots, sewellels, etc. A remnant of a more ancient world, especially characteristic of the Miocene, is found in the remarkable burrowers, the horned †mylagaulids 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, “†bear-dogs,” “†hyena-dogs” and forms like the Dhole of India were common. The terms “†bear-dogs” and “†hyena-dogs” are not to be understood as implying any relationships of these animals to bears or hyenas, but merely a certain superficial resemblance; these were very large members of the dog family (Canidæ), 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. †Sabre-tooth tigers and true cats, some as large as lions and one species fairly gigantic, were likewise characteristic of the time. There 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 seems to be utterly exotic to North America, that of the rhinoceroses, 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 (†Ancylopoda), 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 ancestral 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 remarkably 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 “†deer-antelopes,” now extinct, was represented by _†Merycodus_, 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, 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 †oreodonts, which were wonderfully numerous and varied from the upper Eocene onward, are found here.

The †mastodons (_†Gomphotherium_) 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 †ground-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 †ground-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, rhinoceroses, camels, etc., can be employed only in a very comprehensive 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 same as that of the Pleistocene and contained a similarly large proportion of migrant elements from the north, but it was evidently 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 Artiodactyla, 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, †mastodons, 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 Tasmanian 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 †glyptodonts and some gigantic armadillos, as well as numerous examples of normal size; the †ground-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 the largest known representative of the order. Especially characteristic was the abundance of the cavy family (Caviidæ).

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. Forerunners 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 specialization. We find here also the last survivors of another family of the †Litopterna, the †proterotheres (†Proterotheriidæ), 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 (_†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 (_†Trigodon_) had the interesting peculiarity of a single median horn on the forehead, much like that of a rhinoceros. Horned species were always rare among the indigenous groups of South American ungulates, and all that have been discovered so far belonged to the †toxodonts. The remaining group, that of the †Typotheria, was also well represented, both by larger and by very small forms, some no larger than a rabbit (_†Pachyrukhos_).

The presumably lower Pliocene (perhaps upper Miocene) fauna of the Paraná formation is as yet known only from very fragmentary material. Representatives of the dogs, raccoons and bears have been reported, but the identifications are doubtful; 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 †ground-sloths and †glyptodonts, 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, some of which were large. There were many †typotheres, both of the larger and smaller kinds. The †Litopterna were represented both by the horse-like †proterotheres and the long-necked †macrauchenids, the latter smaller and less specialized than those of the Pampean.

[Illustration: FIG. 124.—Head of Horned †Toxodont (_†Trigodon gaudryi_). Pliocene of Monte Hermoso. Restored from a skull in the Ameghino collection.]

2. _Miocene_

_North America._—Upper Miocene beds cover extensive areas of the Great Plains region and are scattered from Montana far into Mexico. The rich fauna is an outgrowth and development of that of the middle Miocene, with but few immigrant 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 incompletely 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 understood in a broad sense. Hares, mice, pocket-gophers, squirrels, marmots, beavers and the extraordinary †mylagaulids were all abundant.

In even more strongly marked sense must the broad meaning for the vernacular names of the other mammals be emphasized, 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 †sabre-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 †mastodons 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 †mastodons, but the tusks were different from those of the larger members of the group. The upper tusks were comparatively 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 compensated for by the great elongation of the lower jaw. The 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 attained substantially their modern grade of structure, advance among the Proboscidea being chiefly restricted to the teeth and skull.

[Illustration: FIG. 125.—_†Teleoceras 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.]

Four families of Perissodactyla were represented in the upper Miocene. The rhinoceroses, which were very abundant, 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 proportions, 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 †chalicotheres, 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 dominant 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 enlarged 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 American llamas. †Giraffe-camels have not 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 †oreodonts 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 †oreodonts in the altogether exceptional form of the skull. Grazing †oreodonts (_†Merychyus_), of moderate and small size with high-crowned teeth, were evidently quite common on the upper Miocene plains. The †hornless deer and “†deer-antelopes” differed but little from those of the lower Pliocene. Peccaries were fairly abundant.

[Illustration: FIG. 126.—_†Procamelus elrodi_, a large camel from the upper Miocene. Restored from specimens in the Carnegie Museum.]

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, as was first pointed out by Kowalevsky, the explanation is probably to be found in the spread of grassy plains at the expense 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 which occur 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 contemporaneous, 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 †ground-sloths yet discovered 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 †Mylagaulidæ, the presence of which was noted in the upper Miocene and lower Pliocene, first appeared here. These †mylagaulids, 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, as in 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 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 †sabre-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 Proboscidea, the most ancient of which that are definitely determinable 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 proboscideans, but they were doubtless small †mastodons 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 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 grazing 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 animals found in the European Miocene. Of the peccaries little more can be said than that they were present in these faunas. The †oreodonts were very numerous, both individually and generically; two stages of the proboscis-bearing kind are found here together, the older, long-faced genus (_†Promerycochœrus_) 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 †hornless deer and the antlered †deer-antelopes were much like those of the Upper Miocene, slender and graceful little creatures, and there were also considerably larger ruminants (_†Dromomeryx_) with straight, simple and non-deciduous horns, which may be called antelopes.

[Illustration: FIG. 127.—Gigantic †giraffe-camel (_†Alticamelus altus_) from the middle Miocene of Colorado. Restored from specimens in the American Museum of Natural History.]

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 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 together. 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 central Wyoming. The fauna was almost entirely a development from that of the North American Oligocene, with very little admixture of foreign elements, so that the land communication 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.

[Illustration: FIG. 128.—Most ancient American Antelope (_†Dromomeryx antilopina_), middle Miocene. Restored from specimens in the Carnegie Museum and Princeton University.]

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 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 considerable 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 †sabre-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 (Procyonidæ) 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 specimens 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 (_†Cænopus_) 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 †chalicotheres (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. _†Moropus_, 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. 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 †chalicotheres are sufficient evidence that their very unusual structure must 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.

[Illustration: FIG. 129.—The small, †paired-horned rhinoceros (_†Diceratherium cooki_) of the lower Miocene. Restored from a skeleton in the Carnegie Museum, Pittsburgh.]

[Illustration: FIG. 130.—A †chalicothere (_†Moropus elatus_) of the lower Miocene. Restored from a skeleton in the Carnegie Museum, Pittsburgh.]

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 conspicuous group throughout the Oligocene. The lower Miocene genus, _†Dinohyus_, 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 but two toes. The †oreodonts were present in great numbers, both small and large forms; except for bodily stature and modifications of the head, they all looked very much alike; _†Merycochœrus_, with its incipient proboscis, here made its first appearance. The last representatives of a family (†Hypertragulidæ) 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 †chalicotheres; 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 (_†Oxydactylus_, _see_ Fig. 209, p. 392), which was larger and apparently the beginning of the †giraffe-camels, was noteworthy 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.

The limits of the _South American_ Miocene are very doubtful. The Paraná formation, here regarded as lower Pliocene, may prove to be more properly referable to the upper Miocene. No other upper Miocene is known.

[Illustration: FIG. 131.—The †gazelle-camel (_†Stenomylus hitchcocki_) of the lower Miocene. Restored from skeletons in the Carnegie Museum, Pittsburgh.]

To the earlier, probably middle, Miocene may be referred the wonderful Santa Cruz fauna of Patagonia. It is extremely 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 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 arboreal forms were rare.

[Illustration: FIG. 132.—Diagram to illustrate the comparative sizes of the Santa Cruz mammals, a modern pointer dog, within the rectangle, to give the scale. 1. _†Cladosictis lustratus_, predaceous marsupial. 2. _†Protypotherium australe_, †typothere. 3. _†Eocardia excavata_, rodent. 4. _†Stegotherium tesselatum_, armadillo. 5. _†Propalæohoplophorus australis_, †glyptodont. 6. _†Hapalops longiceps_, †ground-sloth. 7. _†Thoatherium minusculum_, †litoptern. 8. _†Astrapotherium magnum_, †astrapothere. 9. _†Prothylacynus patagonicus_, predaceous marsupial. 10. _†Theosodon garrettorum_, †litoptern. 11. _†Nesodon imbricatus_, †toxodont.]

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, crocodiles, or tortoises, and we have no information as to the plant-life of the region at that time. The mammals were almost 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._ _†Prothylacynus_) were as large as wolves and were closely similar to the so-called Tasmanian Wolf (_Thylacynus_). Another genus (_†Borhyæna_) had a short, bullet head, not unlike a small Puma in appearance and, besides, there were many smaller beasts of prey, in size like badgers and minks. Opossums were common and there were many very small herbivorous marsupials, which resembled, though perhaps but superficially, the Australian phalangers. At the present day South America contains no Insectivora, but in the Santa Cruz there was one family (†Necrolestidæ) 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 American families. There were none of the northern forms of rodents, 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, †glyptodonts and †ground-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 †glyptodonts were all small, 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 successors. The †ground-sloths were present in actually bewildering 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 †ground-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 regarded as orders or suborders, a matter of very secondary importance. Individually, the commonest of the hoofed mammals were the †Toxodonta, 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 small median horn on the forehead. As with the †glyptodonts and †ground-sloths, the contrast in size between the Santa Cruz ancestors and the 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 †typotheres 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 †toxodonts. Still a third group of the same series, the †Entelonychia, is of great interest, for, as in the †chalicotheres 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 powerful 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 transformation proceeded independently. Among the perissodactyls the †chalicotheres (p. 238) underwent this change; in North America the †Agriochœridæ, a family of artiodactyls, had a very similar history, while in South America the †Entelonychia arose from the same stock as the †toxodonts, 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 †Astrapotheria, 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 relationships are still obscure; much more complete material must be obtained before this problem can be definitely solved. Both the †Astrapotheria 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 went back to the earliest South American Tertiary. In the Miocene and Pliocene the order was represented by two very distinct families, the †Macrauchenidæ and †Proterotheriidæ, which were superficially very unlike. In the Santa Cruz beds is found a genus (_†Theosodon_) which was apparently the direct ancestor of the Pampean _†Macrauchenia_. The Miocene genus was a much smaller animal and had hardly more than an incipient proboscis, but otherwise was very like its Pampean 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 †proterotheres, 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_, _†Proterotherium_) the feet were three-toed and most surprisingly horse-like in shape, but one genus (_†Thoatherium_) 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 †proterotheres 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.

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 †sabre-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 _†Archælurus_) which have been called the “false †sabre-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 distinguished, 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 (Aplodontiidæ).

The remainder of the known John Day fauna was composed 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 perissodactyls 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 †diceratheres, 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 reason 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 †chalicotheres, 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 perissodactyls. The peccaries were numerous, but smaller and more primitive than those of the succeeding age, as were also the †giant pigs, or †entelodonts, but the latter were very large. The peculiarly North American family of the †oreodonts was very numerously represented, and one genus (_†Promerycochœrus_), comprising animals not unlike the Wild Boar in size and shape, was the probable beginning of the series of proboscis-bearing †oreodonts, which led to such grotesque forms in the middle and upper Miocene. A family closely allied to the †oreodonts, and by many writers included in the latter, is the very remarkable group of the †Agriochœridæ, which was distinguished 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 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 (_†Hypertragulus_) 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 continent 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 designate animals more or less distantly allied to those of the present day.

[Illustration: FIG. 133.—1. _†Archæotherium._ 2. Ancestral camel (_†Poëbrotherium_). 3. _†Merycoidodon._ 4. _†Agriochœrus._ 5. Ancestral horse (_†Mesohippus_). 6. _†Hoplophoneus._ 7. _†Bothriodon._ 8. _†Hyænodon._ 9. †Cursorial rhinoceros (_†Hyracodon_). 10. _†Protoceras._ 11. Hornless rhinoceros (_†Cænopus_).]

Several species of opossums, some of them very small, were the only marsupials in North America then, as they are now. 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 †Creodonta, that had played a great rôle in the Eocene and Paleocene of North America and Europe. In White River times but a single family (†Hyænodontidæ), with two genera, remained of the Eocene host. One of these genera (_†Hemipsalodon_), 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, _†Hyænodon_, 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 disproportionately 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 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.

[Illustration: FIG. 134.—White River †titanothere (_†Titanotherium robustum_) reduced to the same scale as Fig. 133.]

Coincident with this decline of the †creodonts 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 (_†Daphœnus_) and possibly also of the foxes (_†Cynodictis_) 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 †sabre-tooth cats (_†Dinictis_ and _†Hoplophoneus_) all of which, except in the uppermost substage, were quite small, few of them exceeding the Canada Lynx in size. A much larger animal (_†Eusmilus_, also European) appeared in the latter part of the stage. None of the true cats, or feline subfamily, has been obtained. Nothing is yet known of the time and place of origin of the †sabre-tooth series, for they appeared 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. 234), but Egypt has given no help in the case of the †sabre-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 remnant 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.

The hoofed mammals were present in fairly bewildering variety, but were restricted to the two orders of the Perissodactyla 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 †titanotheres 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 sometimes put into two separate families. One of these series, the †hyracodonts (_†Hyracodon_), 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 †amynodonts (_†Metamynodon_), formed the very antithesis of the first,—large, heavy, short-necked, and short-legged and probably amphibious in manner of life, they were armed with formidable tusks; and their skulls were so curiously modified as to bear a distinct resemblance to the skull of a huge carnivore. The †amynodonts migrated to the Old World and occur in the Oligocene of France, but the †hyracodonts would seem never to have left North America. The third series, that of the true rhinoceroses, comprised several genera at different levels in the White River beds (_†Trigonias_, _†Cænopus_, 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 hornless, 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 †paired-horned rhinoceroses (_†Diceratherium_) which so flourished in the John Day and the lower Miocene.

[Illustration: FIG. 135.—†Hornless rhinoceros (_†Cænopus tridactylus_) of the White River stage. Restored from a skeleton in the American Museum.]

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 successive 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 grinding teeth show that they were browsers, not grazers. The abundant Eocene family of the †Lophiodontidæ made its last appearance in the White River, where it was scantily represented 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 horses 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 †chalicotheres 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 considerably smaller. Of the camels, there were two series, one of which (_†Eotylopus_), lately described by Dr. Matthew, is of yet unknown significance, while the other (_†Poëbrotherium_) was apparently the ancestor common to all the subsequent phyla of camels and llamas. 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 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 †Hypertragulidæ, were a greatly diversified group of dainty little creatures, one of which (_†Hypisodus_) was no larger than a rabbit and had high-crowned teeth. The other genera (_†Leptomeryx_, _†Hypertragulus_) 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 †oreodonts 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 _†agriochœrids_ were very much less common; they may be described roughly as †oreodonts with very long, cat-like tails and clawed feet.

[Illustration: FIG. 136.—_†Merycoidodon culbertsoni_, the most abundant of White River †oreodonts. Restored from a skeleton in the American Museum of Natural History.]

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 derived. The unquestionably Old World family, that of the †anthracotheres, was represented in the White River by two genera (_†Bothriodon_ and _†Anthracotherium_), which were short-legged, long-snouted, swine-like animals, which have no near relations in the modern world. The other family, the †giant 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 (_†Archæotherium_) 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.

[Illustration: FIG. 137.—†Giant pig (_†Archæotherium ingens_) from the lower White River stage. Restored from a skeleton in the museum of Princeton University.]

_South America._—The older continental Tertiary formations 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 Cretaceous 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 same three suborders are found in both formations. One of the few †ground-sloths that have been obtained was very large (_†Octodontherium crassidens_), a much larger animal than any species of the suborder that is known from the Santa Cruz. The †glyptodonts were also rare, and only two genera and species have been described from very scanty remains. Armadillos, 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 discovered in South America and represent only two families, both belonging to the Hystricomorpha, or porcupine group. If, as Dr. Schlosser and other European palæontologists maintain, 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 belonging to the typically South American groups. The †Toxodonta 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 †Notohippidæ, which had highly complex, cement-covered grinding teeth. Still a third family of this suborder, the †Leontiniidæ, 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 ancestral to the Santa Cruz genera, larger ones which died out without leaving successors and one quite large animal (_†Eutrachytherus_) 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.

[Illustration: FIG. 138.—Horned †toxodont (_†Leontinia gaudryi_), Deseado stage. Restored from a skull in the Ameghino collection.]

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 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, _†Pyrotherium_, included large, relatively short-legged and very massive 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 †pyrotheres have actually been regarded as the beginnings of the †mastodons and elephants, but this is undoubtedly an error. The †Astrapotheria, another group which became extinct at or soon after the end of the Santa Cruz, were relatively 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 †proterotheres 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 †macrauchenids were quite similar to those of the latter formation, 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 †toxodonts and †typotheres, 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 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 significant 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 collections and include only two families, one the †ischyromyids, 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 (Geomyidæ). The archaic flesh-eaters, or †Creodonta, were represented by two families, one comprising smaller animals with somewhat cat-like, shearing teeth (†Oxyænidæ), the other, very large beasts with crushing teeth (†Mesonychidæ), neither of which continued into the White River. As compared with the middle and lower Eocene, the †creodonts 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 †sabre-tooths or mustelines has been found. Indeed, it is very doubtful whether members of these families ever will be found in the Uinta, for their 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 †titanotheres (_†Diplacodon_, _†Protitanotherium_) were much smaller and lighter than those of the lower White River and had much shorter horns. The †hyracodonts, the lightly built, cursorial rhinoceroses, were represented by a genus (_†Triplopus_) which was smaller and more slender than the White River form (_†Hyracodon_) and its teeth were of distinctly more primitive character. The heavy, massive and presumably aquatic †amynodonts (_†Amynodon_) were likewise smaller and less specialized than their descendants of the Oligocene. No member of the true rhinoceros 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 (_†Epihippus_), like the other families mentioned, were much smaller and distinctly 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 perissodactyls and, with the exception of the peccaries and †anthracotheres, representatives of all the White River families are known. The finding of the peccaries is merely a question of further exploration, but the †anthracotheres 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 †giant-pigs or †entelodonts, 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 evolutionary point of view. The ancestral camel (_†Protylopus_) was a little creature no bigger than a fox-terrier, though the †hypertragulids (_†Leptotragulus_) were as large as _†Leptomeryx_ and _†Hypertragulus_ of the White River. The most ancient known members of the †oreodonts (_†Protoreodon_) and the †agriochœrids (_†Protagriochœrus_) 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 indigenous and so radically distinct from the mammals of corresponding 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 comparative 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 zoölogically 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 †Tæniodontia, which had so many points of resemblance to the †ground-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, 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 Carnivora 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 (†Oxyænidæ) 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 †Hyænodontidæ) comprised small, long-headed, fox-like and weasel-like animals, which doubtless preyed upon small mammals and birds. A third family (†Mesonychidæ) 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 †Miacidæ, a family which connected the †creodonts and true carnivores and might almost equally well be placed in either group, were externally much like the small †hyænodonts, but were more efficiently equipped for the capture and devouring of prey.

[Illustration: FIG. 139.—A mesonychid †creodont (_†Dromocyon velox_) of the Bridger stage. Restored from a skeleton in the Museum of Yale University.]

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 †Amblypoda, one family of which (†Uintatheriidæ) was preëminently characteristic of middle Eocene life, becoming very rare and then dying out in the upper Eocene. The †uintatheres of the Bridger underwent considerable modification in size and appearance within 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 lower jaw; bony knobs on the end of the nose probably supported a pair of dermal horns like those of a rhinoceros and, in addition, a pair of high, cylindrical, horn-like, bony protuberances 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 †uintatheres, 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 †ischyromyids, 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 (_†Paramys_) 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 dominating importance. There were five or six families of perissodactyls 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 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 commonest of the genera in the middle and lower Bridger was _†Palæosyops_, which was hornless, while in the upper part of the beds are found genera (_e.g._ _†Manteoceras_ and _†Dolichorhinus_) in which the horns were just beginning to appear. Another extinct family, the †Lophiodontidæ, 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._ _†Helaletes_).

[Illustration: FIG. 140.—Some characteristic mammals of the Bridger Eocene reduced to a uniform scale, with a pointer dog, in frame, for comparison. 1. Primitive rhinoceros (_†Hyrachyus eximius_). 2. †Tritemnodon agilis. 3. _†Patriofelis ferox_, and 4, _†Dromocyon velox_, †creodonts. 5. Primitive rodent (_†Paramys delicatior_). 6. _†Uintatherium alticeps._ 7. †Titanothere (_†Mesatirhinus superior_).]

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 †hyracodonts, or cursorial rhinoceroses, were very abundantly represented by a number of small and medium-sized animals (_†Hyrachyus_) 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 (_†Colonoceras_) 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 _†Triplopus_, with three-toed fore foot; and in the same division occurs another Uinta genus, _†Amynodon_, the most ancient known species of the supposedly aquatic rhinoceroses. True rhinoceroses, 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 relatively common, but are still very incompletely known. The earliest known members of the clawed †chalicotheres were of Bridger date.

It is worth remarking that, except a single genus in the upper and later portion of the stage (_†Triplopus_), all of the 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 (_†Homacodon_), 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 (_†Achænodon_) allied, but not ancestral, to the †giant-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 statement applies, _à 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, cursorial, 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 stratigraphical position, the Wind River fauna was largely transitional between that of the Bridger above and that of the Wasatch below. Unfortunately, the fossils are far less numerous 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 numerical 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 †tillodonts, †tæniodonts and insectivores differed little from the Wasatch representatives of these orders, except that the Bridger †tæniodont, _†Stylinodon_, which had rootless, persistently growing teeth, was associated with the Wasatch genus _†Calamodon_. On the other hand, the primitive flesh-eaters, or †creodonts, which were referable to Wasatch families, were less numerous and varied and formed a mixture of Bridger and Wasatch genera. The †Oxyænidæ, the family with cat-like teeth and head, had both the smaller Wasatch genus _†Oxyæna_ and the very large Bridge _†Patriofelis_. Of the blunt-toothed †Mesonychidæ, one very large animal (_†Pachyæna_) survived from the Wasatch. The small forms of the family †Hyænodontidæ were common, and there were numerous species of the progressive family †Miacidæ.

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 †Amblypoda, was represented by two very different families, one of which, the †uintatheres, was so flourishing in the Bridger, where it formed the most characteristic and by far the most striking element of the fauna. The Wind River genus (_†Bathyopsis_) was a very much smaller animal than any of the Bridger forms and its horn-like protuberances 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 _†Coryphodon_, 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 intermediate in size and structure between those of the Bridger and those of 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 †titanotheres, the family which became 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 (_†Eotitanops_), the very probable ancestor of all the subsequent genera, was quite small, about two-thirds the size of a modern tapir, while the other (_†Lambdotherium_) was a much smaller, lighter and more slender animal and apparently belonged to an abortive, short-lived phylum. Then, too, the first of the †hyracodonts, or cursorial rhinoceroses, made their appearance here in the genus _†Hyrachyus_, 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 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 †titanotheres and †hyracodonts, 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 †Tæniodontia, which bore a certain resemblance to South American edentates, had one pair of incisor teeth above and below enlarged and chisel-shaped, somewhat like those of rodents. The †Tillodontia were much smaller than those of the Bridger, and their incisors were only beginning to take on the chisel-like form. Insectivora were quite abundant, and three, or perhaps four, families were represented in the Wasatch; some of these resembled the modern aquatic insectivores of the west African rivers and others were more like European hedgehogs.

The flesh-eaters all belonged to the †Creodonta, 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. For the most part, the families were the same as those of the Bridger †creodonts, but the genera all were different. The †oxyænids (_†Oxyæna_) 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 predaceous animals (_†Palæonictis_) which also inhabited Europe, but did not survive the lower Eocene in either continent, had short, broad and very cat-like heads. The †mesonychids were far larger than those of the Bridger, a departure from the ordinary rule, and the several species of the common Wasatch genus (_†Pachyæna_) had grotesquely large heads. A family (†Arctocyonidæ), of very extensive geographical range and great antiquity, had its last representatives here in a very curious animal (_†Anacodon_) which had the flat-crowned, tuberculated grinding teeth of the bears and the enlarged, scimitar-like upper canines of the †sabre-tooth cats. Such a combination seems utterly incongruous and no one would have ventured to predict it. The progressive family of †creodonts (†Miacidæ) was already quite numerously represented, but only by small forms, which must have preyed upon small mammals, birds and lizards.

Two archaic orders of hoofed mammals were fairly numerous. 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 †Amblypoda, one genus of which (_†Coryphodon_), though persisting into the Wind River, was especially characteristic of the Wasatch. The †coryphodonts 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 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 †uintatheres, have not yet been registered from the Wasatch, but they will undoubtedly be found there, as they were unquestionably present at that time.

[Illustration: FIG. 141.—_†Phenacodus primævus_, the best known Wasatch representative of the †Condylarthra. Restored from a skeleton in the American Museum of Natural History.]

[Illustration: FIG. 142.—The commonest of Wasatch ungulates, the †amblypod, _†Coryphodon testis_. Restored from a skeleton in the American Museum of Natural History.]

All of the preceding groups were of the archaic, non-progressive type and have long been extinct. With the sole exception of one †creodont family (†Miacidæ) and perhaps some of the insectivores, they have no descendants or representatives 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 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 (†Ischyromyidæ) 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 Artiodactyla. Of the former was a genus (_†Eohippus_) of the most ancient American horses. These most interesting little animals, 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 _†Eohippus_ 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 †Lophiodontidæ, 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 skeleton is of so indifferent a character that the reference of this genus to the tapirs cannot be positively made.

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 (_†Trigonolestes_), 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 (_†Eohyus_), considerably larger, is very doubtfully referable to the pigs; while a third (_†Parahyus_), still larger, was the first in the short-faced series of the †entelodonts, which persisted in ever increasing size through the whole Eocene, but could hardly have been ancestral to the true †entelodonts, or †giant-pigs, of the Oligocene, the place and time of whose origin are unknown.

Another immigrant order of great interest, since we ourselves 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 (_†Anaptomorphus_) had a remarkable 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 succeeding Astraponotus Beds is still but a scanty list. This list, however, includes the most ancient †glyptodonts yet discovered and the most ancient †astrapotheres 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 _Cænolestes_, 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 †ground-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 †toxodonts, in the more restricted sense of that term, have been found, but the two allied suborders of the †Typotheria and †Entelonychia 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 †Entelonychia (†Notostylopidæ) consisted of very small, rodent-like animals, with a pair of chisel-shaped incisors in upper and lower jaw, and a second family (†Homalodontotheriidæ) 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 †astrapotheres, 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 †Condylarthra. However, until something is ascertained regarding 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 comparative 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 remarked that it contained none of the immigrant orders.

The vegetation of the Paleocene was already very modern in character, and nearly all of the common forest-trees 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 development, and, as we have already learned, eventually led to widespread 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, unexplained 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 herbivorous marsupials, with very complex grinding teeth and chisel-like incisors, but no carnivorous or insectivorous members of the order have been found. Insectivora were present. Of the †creodonts, or primitive flesh-eaters, there were no less than five families; the bear-like †Arctocyonidæ, which died out in the Wasatch, were quite numerous, and the problematical †Mesonychidæ were much smaller and more primitive mammals than those of the Eocene. Passing over two families which did not survive the Torrejon, we may note the first of the †Miacidæ, the progressive family which led eventually to the true Carnivora. The hoofed animals all belonged to the archaic †Condylarthra and †Amblypoda; 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 †coryphodonts and the †uintatheres of the Eocene.

[Illustration: FIG. 143.—The Torrejon forerunner (_†Pantolambda bathmodon_) of _†Coryphodon_. Restored from a skeleton in the American Museum of Natural History.]

The _Puerco_ fauna was much like that of the Torrejon, but even less advanced and diversified. The herbivorous marsupials were more abundant, and some of them (_†Polymastodon_) larger than those of the Torrejon; Insectivora may have been present, but this is doubtful. The †creodonts, so far as they have been discovered, were less numerous, varied and specialized than those of the Torrejon and included but one of the families which passed over into the Eocene. The †Condylarthra were much less common and the †Amblypoda but doubtfully represented, but the edentate-like †Tæniodontia were conspicuous.

[Illustration: FIG. 144.—Head of an †allotherian marsupial (_†Polymastodon taöensis_) from the Puerco stage. Restored from a skull in the American Museum of Natural History.]

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 †Condylarthra, †Amblypoda and †Creodonta, developed greatly and played an important part in the life of the Eocene, but of these only a few †creodonts 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.