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 lambei horse, not an ass. The closest resemblance to "E." "lambei" is shown by the Mongolian horse, "E. caballus przewalskii", now believed to be extinct in the wild. In size and proportions, "E. lambei" resembles "E. caballus przewalskii". Among living horses, perhaps the Yukon horse most closely resembles the Przewalski's horse ("Equus caballus przewalskii") from Mongolia . The upper foot bones (metapodials) of "Equus lambei" are slender compared to Przewalski's horse. The bones of "E. lambei" also closely resemble the proximal phalanges of "E. caballus lenensis", an extinct species from the late Pleistocene of Siberia . Along with steppe bison ("Bison