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In the middle Eocene they roamed in vast herds from Oregon to Kansas and Nebraska. THE RUMINANTS. This division of the artiodactyls includes antelopes, deer, oxen, bison, sheep, and goats, all of which belong to a common stock which took its rise in Europe in the upper Eocene from ancestral forms akin to those of the camels.
The proboscidians culminated in the Pliocene, when some of the giant elephants reached a height of fourteen feet. THE ARTIODACTYLS comprise the hoofed Mammalia which have an even number of toes, such as cattle, sheep, and swine. Like the perissodactyls, they are descended from the primitive five-toed plantigrade mammals of the lowest Eocene.
Along the main line of the evolution of the artiodactyls the side toes, digits two and five, disappeared, leaving as proof that they once existed the corresponding bones of palm and sole as splints. The TWO-TOED ARTIODACTYLS, such as the camels, deer, cattle, and sheep, are now the leading types of the herbivores.
In their evolution, digit number one was first dropped, and the middle pair became larger and more massive, while the side digits, numbers two and five, became shorter, weaker, and less serviceable. The FOUR-TOED ARTIODACTYLS culminated in the Tertiary; at present they are represented only by the hippopotamus and the hog.
Nearly all have horns or antlers, at least in one sex. Most split-hoofed animals are ruminants, but there is a small remnant, probably of early types, which are not. Non-ruminants Hippopotamus, Swine, Peccaries. Ruminants Camels, Llamas, Chevrotains, Giraffe, Antelopes, Sheep, Goats, Musk-ox, Oxen, Deer. The non-ruminant artiodactyls need not detain us long.
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