Miohippus

The ancestral horse Miohippus, in an artist's conception. Existing toe bones of the forefoot are numbered outward from the centre of the body.

Miohippus, genus of extinct horses that originated in North America during the Late Eocene Epoch (37.2–33.9 million years ago). Miohippus evolved from the earlier genus Mesohippus; however, the former was larger and had a more-derived dentition than the latter. The number of toes in Miohippus was reduced to three, which enabled it to run considerably faster than its five-toed ancestors. Miohippus persisted into the Miocene Epoch (23–5.3 million years ago) side by side with its more horselike one-toed relatives.