Equus (genus) 54 million years ago (Mya). These animals had three toes on the hind feet and four on the front feet with small hooves in place of claws, but also had soft pads.<ref name="doi10.1126/science.1105458"></ref> Equids developed into larger, three-toed animals (e.g. "Mesohippus") during the Oligocene and Miocene. From there, the side toes became progressively smaller through the Pleistocene until the emergence of the single-toed "Equus". The genus "Equus", which includes all extant equines, is believed to have evolved from "Dinohippus", via the intermediate form "Plesippus". One of the oldest species is "Equus simplicidens", described as zebra-like with a donkey-like head shape.
Equus conversidens Equus conversidens Equus conversidens (Owen 1869), or the Mexican horse, is a dubious Pleistocene species of horse, now extinct, that inhabited North America. The holotype of "Equus conversidens", a partial palate, was unearthed in Pleistocene deposits northeast of Mexico City, Mexico. In January 1963, a partial skeleton was found in the city of Canyon, Texas in a white clay bed during the excavation of a basement, and was referred to "E. conversidens" by Dalquest and Hughes (1965), who interpreted the species as medium to small-sized, and added additional records of the species from Texas (including a skeleton from Slaton), Arizona,