- the earliest known horse, a member of the extinct genus Hyracotherium (Eohippus), from the early Eocene Epoch of the Northern Hemisphere; a terrier-sized herbivore having four hoofed toes on each forefoot and three on each hind foot, and low-crowned teeth.
- the earliest horse: an extinct Eocene dog-sized animal of the genus with four-toed forelegs, three-toed hindlegs, and teeth specialized for browsing
