The evolutionary lineage of the horse is among the best-documented in all paleontology.
The history of the horse family, Equidae, began during the Eocene Epoch, which lasted from about 56 million to 33.9 million years ago.
During the early Eocene there appeared the first ancestral horse, a hoofed, browsing mammal designated correctly as Hyracotherium but more commonly called Eohippus.
The “dawn horse.” Fossils of Eohippus, which have been found in both North America and Europe, show an animal that stood 4.2 to 5 hands (about 42.7 to 50.8 cm, or 16.8 to 20 inches) high, diminutive by comparison with the modern horse, and had an arched back and raised hindquarters.
The legs ended in padded feet with four functional hooves on each of the forefeet and three on each of the hind feet—quite unlike the unpadded, single-hoofed foot of modern equines.