Name: Pliohippus Name: Pliohippus Pliohippus lived about 12 million years ago in North America. It had evolved into the first one-toed horse, and the 2 side toes had been reduced to splint bones. As a result, it was the forerunner of the modern day horse. This became an endpoint branch as it died out in the Pliocene. It developed from Merychippus of the Miocene period.
It was a grazing animal in North America with high-crowned teeth and in turn it gave rise to Dinohippus which in turn evolved into Equus, the modern horse.
Its skull had a depression in the skull, called the pre-orbital depression, located in front of the eyes and the function of this is not really known. Some have suggested it was for the attachment for specialized lip muscles, but others have suggested this depression may have played a role in vocalizations.