Mesohippus Skull, replica

Mesohippus Skull. Mesohippus bairdii. REPLICA, 202mm/8.0in. Oliogocene horse. White River Formation, Nebraska.

Mesohippus (Greek: meso meaning "middle" and hippus meaning "horse") lived some 40 million years ago in the mid- Oligocene. It had longer legs than its predecessor Hyracotherium and stood about two feet tall. It had also lost a toe and now stood predominantly on its middle toe, although the other two were also used. The face of Mesohippus was longer and larger than earlier equids. It had a slight facial fossa, or depression in the skull. The eyes were rounder and were set wider apart and farther back. Like many fossil horses, Mesohippus was common in North America. Mesohippus trigonostylus skull. Mesohippus trigonostylus skull.

Its teeth were also larger and contained a single gap behind the front teeth, where the bit now rests in the modern horse. In addition, it had another grinding tooth, making a total of six. Like Hyracotherium, Mesohippus was a browser that fed on tender twigs and fruit. The cerebral hemisphere, or cranial cavity, was notably larger than that of its predecessors; its brain was like that of today's horse.

Mesohippus was extinct by the mid-Oligocene period.