CREATION BY EVOLUTION
groups named. They were all three toed, but the side toes in most species were so small that they did not touch the ground. Pliohippus, which lived only in North America, had the smallest side toes; Hipparion, which lived in North America and in Europe, had the largest side toes and had teeth of a distinctive pattern.
In the Pleistocene epoch, which followed the Pliocene and which included the Ice Age, horses were abundant in both America and Europe. These horses, which were presumably the descendants of Pliohippus, are so nearly like the horses now living that they have all been placed in the genus Equus. Pleistocene deposits found in all parts of the United States, from California through Texas to Florida and northward to Nebraska and Pennsylvania, have yielded remains of horses, some smaller than even the smallest living pony, some as large as any living horse, and one species (Equus giganteus) the largest horse known.
The Pleistocene epoch is the period of maximum development of the horses in number, size, and variety. During this epoch horses made their way from America by way of Alaska and an isthmus across Bering Sea to Asia and Europe. Remains of Pleistocene horses are found in Alaska. The ice sheet of the glacial age, although it covered northeastern America, did not extend west of the Rocky Mountains, so that Alaska was then temperate enough to permit horses to live there. During this epoch horses made their way also to South America over the Isthmus of Panama and spread as far south as Argentina.
The most notable evolutionary changes in the horses consist of an increase in size, changes in the size and structure of the teeth, and, most conspicuous of all, changes in the form of the foot. The stock from which the horse was derived was probably five-toed, the foot conforming in its
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