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 (weapon) could be winched back again. The onagers of the Roman Empire were mainly used for besieging forts or settlements. They would often be armed with large stones that could be covered with a combustible substance and set alight. The onager was used from the 4th century AD until the 6th century AD. The late-fourth century author Ammianus Marcellinus describes 'onager' as a neologism for scorpions and relates various incidents in which the engines fire both rocks and arrow-shaped missiles. The late-fourth or early-fifth century military writer Vegetius stipulates that a legion ought to field ten onagers, one for each cohort.