Horse outward similarity is an unreliable measure of relatedness. Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
Proconsul africanus has a talus in which the trochlear surface is highly curved and deeply grooved. The foot of this species possessed a transverse arch. "Proconsul africanus" had a brachial index of 96 which is comparable to the extant genus "Pan". Overall the skeleton of this species can be described as being robust. This species had an average body mass of around . Based upon the dental morphology, it is conjectured that "Proconsul africanus" was a frugivorous species. A study by Aiello in 1981 concluded it was a "below-branch feeder." Based on postcranial pieces, "Proconsul africanus" was likely an arboreal quadruped. Proconsul