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,
Australopithecus africanus Little Foot is currently classified as (lumped into) "Australopithecus africanus"; Clarke suggests that Little Foot doesn't belong to either species "afarensis" or "africanus," but to a unique "Australopithecus" species found at Makapansgat and Sterkfontein (and named "Australopithecus prometheus" by Raymond Dart). Analysis made in 2015 by a new radioisotopic technique dated the Little Foot specimen to about 3.7 mya. "A. africanus" was similar in many traits to "A. afarensis", a bipedal hominin with arms slightly longer than the legs (a physical trait also found in chimpanzees). It has slightly human-like, advanced cranial features (seen in the crania of Mrs. Ples