Eohippus ("dawn horse") is the earliest known horse. It was dog-sized and four-toed. It lived between 60 and 45 million years ago in the Eocene Epoch. Another name for this genus is Hyracotherium ("mole beast").

Eohippus averaged only 2 feet (60 cm) in length and averaged 8 to 9 inches (20 cm) high at the shoulder. It had 4 hoofed toes on the front feet and 3 hoofed toes on each hind foot. The skull was long, having 44 long-crowned teeth. Eohippus is believed to have been a grazing herbivore that ate soft leaves and plant shoots.

They lived in the Northern Hemisphere (in Asia, Europe, and North America). The first fossils of this tiny horse were found in England by the famous paleontologist Richard Owen in 1841. He gave it the name "Hyracotherium."