Hyracotherium was very small (small-dog size) and had four toes on its front legs. Although this genus gave rise to various lineages of horses that included successively larger and faster horses, Hyracotherium was not a runner. Instead, it moved slowly about in forests and relied on its own camouflage rather than swift running in order to protect itself from predators.
|Hyracotherium (length 60 cm = 23 inches).|
Hyracotherium was the first name given to this genus, based on specimens found in England. Later, based on specimens found in North America, it was mistakenly named again; this time as “Eohippus,” which means “dawn horse.” Eohippus is thus a secondary junior synonym of Hyracotherium, and in the international rules of naming of organisms, Hyracotherium has priority because it was named first.
The tooth shown below is a single molar from the lower jaw of Hyracotherium angustidens of Eocene age from Wyoming. Its teeth were low-crowned with low cusps, which enabled the animal to eat both fruit and soft leaves.
|Side view of a molar of Hyracotherium angustidens; specimen is 10 mm length, 5.5 mm height.|
|Top view of molar shown above.|