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.
African wild ass female collected by von Heuglin near Atbarah River, Sudan, and present in the State Museum of Natural History Stuttgart, MNS 32026. The two subspecies recognized are the Nubian wild ass "Equus africanus africanus" (von Heuglin & Fitzinger, 1866), and the Somali wild ass "Equus africanus somaliensis" (Noack, 1884). African wild asses are well suited to life in a desert or semidesert environment. They have tough digestive systems, which can break down desert vegetation and extract moisture from food efficiently. They can also go without water for a fairly long time. Their large ears give them an excellent sense of hearing