Pliohippus is a genus of primitive horse that lived in North America during the Miocene epoch. It resembled a smaller version of the modern day horse and from a distance you weren't able to see the difference. Pliohippus' hooves have been reduced to a single larger hoof and two very small side hoofs, which it didn't used anymore. Also, the skull had two small pits which were probably used to adjust its calls; a trait that lacks in modern day horses. Pliohippus lived on open plains and fed on grass.
The genus of Pliohippus is old and therefore many species have been assigned to the genus. At the time of writing, at least four species are accepted of which Pliohippus pernix is one of the earliest described species. Fossils of this species have been found in the Southern states of the USA, like Texas, New Mexico and South Dakota. Pliohippus could grow up to 1.3 meters at the shoulders.