CHAPTER IX
HISTORY OF THE ARTIODACTYLA
The artiodactyls are and for a very long time have been a very much larger and more variegated group than the peris- sodaetyls, and the Old World has been and still is their head- quarters and area of special development, where they are represented in far greater number and variety than in the New ; the perissodactyls, on the other hand, flourished espe- cially in North America, as was shown in the preceding chapter. At the present time the artiodactyls are the dominant ungulate order, far outnumbering all the others combined, and include an assemblage of varied types, which, when superficially examined, appear to be an arbitrary and unnatural group. What could seem more unlike than a dainty little mouse-deer, no larger than a hare, a stag, a camel, a giraffe, a bison and a hippopotamus ? Yet, in spite of this wonderful diversity of size, proportions, appearance and habits, there is a genuine unity of structure throughout the order, which makes their association in a single group altogether natural and proper, especially as these structural characters are not found united in any other group.
It would be superfluous to enumerate all of the diagnostic characters which, on the one hand, unite all the living and extinct artiodactyls and, on the other, distinguish them from all other hoofed animals, and it will suffice to mention a few of the more significant of these features.
As the name implies, the artiodactyls typically have an even number of toes in each foot, four or two ; though this rule may be departed from and we find members of the order
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