The Perissodactyla are the odd-toed ungulates, that is the number of toes is reduced to three or one (rarely four and then the outer one is weak), due to the fact that the weightbearing axis of the foot passes down the central digit. They were numerous throughout the Tertiary and included the huge horned titanotheres and the clawed chalicotheres which are now extinct. Today the group is represented by three types, the tapir, the rhinoceros and the horse, all reduced to relatively low numbers, at least in the wild, and showing the discontinuous distribution which is characteristic of groups that were once widespread but are now eliminated from much of their former range.
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