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 New Mexico, Oklahoma, Kansas and Florida, synonymizing "Equus francisci", "Equus tau", "E. littoralis", "E. achates", and "E. barcenaei" with "E. conversidens". However, Winans (1985) and MacFadden (1992) challenged the validity of "E. conversidens" due to its minimal diagnostic value, and treated "E. francisci" as valid. Subsequent study confirmed the "nomen dubium" status of "E. conversidens" because the holotype was undiagnostic besides its small size. 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