Fossil range: Early Oligocene
Mesohippus (Greek: μεσο/meso meaning "middle" and ιππος/hippos meaning "horse") is an extinct genus of early horse. It lived some 40 to 30 million years ago from the late Eocene to the mid-Oligocene. Like many fossil horses, Mesohippus was common in North America.
Mesohippus had longer legs than its predecessor Hyracotherium and stood about 60 centimetres (10 h) tall. It had also lost a toe and 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 than in Hyracotherium.
Unlike earlier horses, its teeth 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. 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 similar to that of modern horses.