Onager 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: A sixth possible subspecies, the Gobi khulan ("E. h. luteus", also called the "chigetai" or "dziggetai") has been proposed, but may be synonymous with "E. h. hemionus". Debates over the taxonomic identity of the onager occurred until 1980. As of today, four living subspecies and one extinct subspecies of the Asiatic wild ass have been
Onager ancestor of all modern equids (members of the genus "Equus") lived around 5.6 (3.9–7.8) million years ago (Mya). Direct paleogenomic sequencing of a 700,000-year-old middle Pleistocene horse metapodial bone from Canada implies a more recent 4.07 Mya for the most recent common ancestor within the range of 4.0 to 4.5 Mya. The oldest divergencies are the Asian hemiones (subgenus "E. (Asinus)", including the kulan, onager, and kiang), followed by the African zebras (subgenera "E. (Dolichohippus)", and "E. (Hippotigris)"). All other modern forms including the domesticated horse (and many fossil Pliocene and Pleistocene forms) belong to the subgenus "E. (Equus)" which