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 conversidens Equus conversidens Equus conversidens (Owen 1869), or the Mexican horse, is a dubious Pleistocene species of horse, now extinct, that inhabited North America. The holotype of "Equus conversidens", a partial palate, was unearthed in Pleistocene deposits northeast of Mexico City, Mexico. In January 1963, a partial skeleton was found in the city of Canyon, Texas in a white clay bed during the excavation of a basement, and was referred to "E. conversidens" by Dalquest and Hughes (1965), who interpreted the species as medium to small-sized, and added additional records of the species from Texas (including a skeleton from Slaton), Arizona,