Horse
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".
Onager
The Asiatic wild ass, among Old World equids, existed for more than 4 million years. The oldest divergence of "Equus" was the onager followed by the zebras and onwards. A new species called the kiang ("E. kiang"), a Tibetan relative, was previously considered to be a subspecies of the onager as "E. hemionus kiang", but recent molecular studies indicate it to be a distinct species, having diverged from the closest relative of the Mongolian wild ass's ancestor less than 500,000 years ago.
Widely five recognized subspecies of the onager include: