The subgenus Asinus encompasses four species and several subspecies of equidae characterized by long ears, a lean, straight-backed build, a scant tail and reputed to have considerable toughness and endurance.
The common Donkey or "Ass" is the best-known representative of the Subgenus, with both domesticated and feral varieties, ranging in size from the small burro to the horse-sized "Mammoth Jack" and other breeds. There is not a formal cutoff between the terminology "donkey" and "ass," though smaller animals are usually called donkeys and larger animals are asses. Both can be used to create a mule, which is a hybrid animal produced by a cross of a donkey and a horse.
Wild asses, include a number of truly wild, never domesicated subspecies of Equus Asinus that live in Africa and Asia. The closest relative to Equus africanus is the Grevy's zebra. They have similiarties, including small herds, longer ears and the skull is more ass shape.