Hyracodon Vertebrea, from North America (REF:HVM1)

Hyracodon is extinct genus of perissodactyl (three or one toed)  mammal that though had a pony-like appearance actually represents a form of prehistoric rhino. Dentition of the Hyracodon resembled that of later rhinoceroses.

It had a short, broad snout and its long, slender limbs had three digits. In the Miocene, starting back in the Eocene, the landscape of North America was changing from large expanses of forest to open grasslands. This may in part be why Hyracodon declined and disappeared during the late Oligocene and early Miocene. They died out without leaving any descendants and they mark the end of the phylogenetic branch of hornless, running rhinoceroses.