Orohippus (Gr., "mountain horse")'s an extinct ancestor of the modern horse that lived in the Eocene (about 50 million years ago). It's believed to have evolved from animals like Hyracotherium, as the earliest evidence for Orohippus appears about 2 million years after the first appearance of Hyracotherium. The anatomical differences between the two are slight: they were the same size, but Orohippus had a slimmer body, a more elongated head, slimmer forelimbs and longer hind legs, all of which… (More on Orohippus)