Orohippus lived on the average Eocene the tertiary period. These small, height less half-metre, the horsy, stood right at the beginning of an evolutionary chain of horses. Small manes on these necks horsy were motionless, but tails, overgrown by rare hair, fluttered in air. Forward legs Orohippus were still four-fingered, and back - three-fingereds, and on all fingers were small hoofs. But already at these primitive horsy bones of middle fingers of legs have been advanced more strongly, than lateral.
Orohippus had 15 pairs of ribs. (3 less than Hyracotherium). Teeth: 3 premolars, 4 grinding molars. (one more molar and one less premolar than Hyracotherium.