Fig. 224.—Right manus of the Indian Elephant (E. maximus).
At present, the Proboscidea are restricted to the warmer parts of Asia and Africa, where five species, four of them African, are recognized. This is a very great reduction in the number of species and in the area inhabited during the Pleistocene epoch, when they ranged through every continent, except Australia, and were adapted to every climate from the tropics to the shores of the Arctic Sea. Four distinct species of proboscideans existed in Pleistocene North America, three elephants and a †mastodon, though not all in the same areas, nor probably all at the same time, their ranges both in time and space overlapping to a greater or less degree, but not exactly coinciding in either respect.
Fig. 225.—Vertical section through the manus of the Indian Elephant. U, lower end of ulna. L, lunar. M, magnum. III, third metacarpal. 1, 2, 3, phalanges. E, pad of elastic tissue. (After M. Weber.)
The first species was an immigrant, the northern †Mammoth (Elephas †primigenius), which extended over the greater part of the northern hemisphere, both in the Old World and in the New. This is the species of which complete carcasses with hide and hair have been found in the frozen gravels of northern Siberia, its structure and appearance being thus almost as well known as those of any modern elephant. That the †Mammoth was perfectly adapted to life in a climate of severe cold is shown not only by the contents of the stomach, which are comminuted fragments of present-day Siberian vegetation, but also by the dense coat of woolly hair, covered by long, coarse outer hair, which afforded full protection against the cold. The tusks, with considerable variation of form, had a tendency to spiral curvature, curving first downward and outward, then upward and inward; the grinding teeth were characterized by their relative breadth and the numerous thin enamel-ridges which traversed them. The number of these ridges was very variable in different individuals, but may be expressed for the six successive teeth as follows: 3-4, 6-9, 9-12, 9-15, 14-16, 18-27. The skeleton was more like that of the Indian Elephant than of the other species, though with a number of small differences in the skull. In size, the †Mammoth was comparatively small, standing about nine feet six inches at the shoulders. In North America its range was from Alaska southeastward across the continent to New England.
The second species, the †Columbian Elephant (E. †columbi [Fig. 114, p. 198]), was eighteen inches or more taller than the †Mammoth and rivalled the largest existing elephants in stature; its huge tusks curved first downward and then upward and inward, their tips crossing when full-grown. The grinding teeth had fewer and thicker enamel plates than those of the †Mammoth. The range of the †Columbian Elephant overlapped the southern border of that of the †Mammoth, but was, on the whole, much more southern; it crossed the continent from ocean to ocean and covered nearly the whole of the United States, extending down to the southern end of the Mexican plateau. The two species were very closely related and in some cases are so intergraded that it is difficult to distinguish them; the †Mammoth was an undoubted immigrant and the †Columbian Elephant was probably a local North American variant of it, adapted to a somewhat warmer climate. Nothing is known of the skin or hair in the latter animal, but, from the fact that it was not a tropical species and was exposed to very cold winters, it may be inferred that it had a hairy covering of some sort.
The third species of elephant (E. †imperator) was older geologically than the others, as it was more characteristic of the lower Pleistocene and uppermost Pliocene; its range coincided with the western half of the region covered by E. †columbi, extending far into Mexico, but not occurring east of the Mississippi River. It was an enormous creature, the largest of known elephants, with an estimated height of thirteen and a half feet at the shoulder (Osborn). The grinding teeth had thicker and more crumpled enamel plates than in either of the other species.