Geologic period: Pliocene
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Pliohippus lived in what is now North America during the Pliocene, from 5.3 to 1.6 million years ago. Pliohippus was about the size of a modern donkey, with stiff hair similar to a donkey's. Pliohippus was the first of the single-toes horses and is considered a "grandfather" to modern horses.... although modern horses, Equus, did not develop in North America.