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Some Early Mammals and the Story of the Horse: Pliocene

During the later Tertiary, or Pliocene period, a vast development of the horse tribe took place, so that great numbers of these animals left their remains in the lake-deposits of that time. The largest of these lakes had the Rocky Mountains for its western border, and extended from Dakota to Texas, its northern part covering the bed of the older Miocene basin. Another Pliocene basin, of unknown limits, extended over the older Tertiary strata of Eastern Oregon, and evidence of yet others may be seen in Idaho, Nevada, and California. In all of these fossil horses have been found; but the most important localities are the region of the Niobrara River east of the mountains, and the valley of the John Day River in Oregon (see sketch-map, p. 253).

It will thus be seen how abundant is the material for tracing the evolution of the horse in America. In that country the Equus fraternus of Leidy is believed to be almost, if not entirely identical with the Equus caballus (Linn.) of the old world. Only in the upper Pliocene deposits does the true horse appear, and then the genealogy is complete. It roamed over the whole of North and South America, and soon after seems to have become extinct. There is no doubt that man and the horse were contemporaneous in early days; but it can be proved beyond doubt that, at the time of the Spanish conquest, few if any horses were left. It has been thought, from certain references contained in old narratives, that at least in South America the animal may possibly have still lingered on after the coming of the Europeans. What cause can have led to its extermination, it is impossible to say. The present race of wild SOME EARLY MAMMALS horses, which roam in such vast herds on the Pampas, are not the descendants of the fossil horse of South America, but have sprung from those introduced by the Spaniards more than three hundred years ago.