African wild ass (Equus)" which diverged ~4.8 (3.2–6.5) million years ago. Different authors consider the African wild ass and the domesticated donkey one or two species; either view is technically legitimate, though the former is phylogenetically more accurate. The species name for the African wild ass is sometimes given as "asinus", from the domestic donkey, whose specific name is older and usually would have priority. But this usage is erroneous since the International Commission on Zoological Nomenclature has conserved the name "Equus africanus" in Opinion 2027. This was done to prevent the confusing situation of the phylogenetic ancestor being taxonomically included in its
Equus niobrarensis Equus niobrarensis Equus niobrarensis (or commonly, Niobrara horse) is an extinct species of "Equus", the genus that includes the horse. "E. niobrarensis" may be synonymous with "Equus scotti". It was "stout-legged" and belonged to the "big horses" category as defined by M. C. Winans. The skull of the horse was noted as being broader than Equus caballus. "E. niobrarensis" was native to North America and commonly found in western North America and dates to the late Pleistocene. Fossils of "E. niobrarensis" were discovered at Dry Cave in Wisconsin. Another mention of an "E. niobrarensis" discovery was in Skeleton Cave, Oregon.