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 Equus lambei Equus lambei (common names include Yukon horse, and Yukon wild horse) is an extinct species of the genus "Equus". "Equus lambei" ranged across North America until approximately 10,000 years ago. Based on recent examinations of the mtDNA of "Equus lambei" remains, scientists have concluded that "E. lambei" was probably much like the extinct Tarpan, also known as the Eurasian wild horse, and the living Przewalski's Horse. A partial carcass of "Equus lambei" is on display at the Yukon Beringia Interpretive Centre in Whitehorse, Yukon. Evidence from "E. lambei" mtDNA has shown that "Equus lambei" is a close relative