A history of land mammals in the western hemisphere

by William Berryman Scott

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.

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.

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.)