Protohippus is an extinct three-toed genus of horse.

[3] It was roughly the size of a modern donkey.

Fossil evidence suggests that it lived during the Late Miocene (Clarendonian to Hemphillian), from about 13.6 Ma to 5.3 Ma.

[4] Analysis of Protohippus' skull and teeth suggests that it is most closely related to the genus Calippus.

[4]