Merychippus is an extinct proto-horse of the family Equidae that was endemic to North America during the Miocene, 15.97–5.33 million years ago.

The Miocene was a time of drastic change in environment, with woodlands transforming into grass plains.

[7] The foot was fully supported by ligaments, and the middle toe developed into a hoof that did not have a pad on the bottom.

The transformation into plains also meant Merychippus began consuming more phytolith rich plants.

In later genera, these were lost altogether as a result of the development of side ligaments that helped stabilize the middle toe during running.