Donkey the environment. They may compete with livestock and native animals for resources, spread weeds and diseases, foul or damage watering holes and cause erosion. Few species of ass exist in the wild. The African wild ass, "Equus africanus", has two subspecies, the Somali wild ass, "Equus africanus somaliensis", and the Nubian wild ass, "Equus africanus africanus", the principal ancestor of the domestic donkey. Both are critically endangered. Extinct species include the European ass, "Equus hydruntinus", which became extinct during the Neolithic, and the North African wild ass, "Equus africanus atlanticus", which became extinct in Roman times. There are five subspecies
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.