The onager (, ) (Equus hemionus), also known as hemione or Asiatic wild ass, is a species of the family Equidae native to Asia. A member of the subgenus Asinus, the onager was described and given its binomial name by German zoologist Peter Simon Pallas in 1775. Six subspecies are accepted. The onager is reddish-brown or yellowish-brown and has a broad dorsal stripe on the middle of the back. It weighs about 200–260 kg (440–570 lb) and reaches about 2.1 m (6 ft 11 in) head-body length. It is among the fastest mammals, capable of running 64–70 km/h (40–43 mph). The onager had a wider range from southwest and central to northern Asia including the Levant region, Arabian Peninsula, Afghanistan and Siberia; the prehistoric European wild ass subspecies ranged through Europe until the Bronze Age. During the early 20th century, it lost most of its range in the Middle East and Eastern Asia and lives today in Iran, Kazakhstan, Uzbekistan, Turkmenistan, India, Mongolia and China. It inhabits deserts and arid regions, grasslands, plains, steppes, and savannahs. Like many other large grazing animals, its range has contracted greatly under the pressures of poaching and habitat loss. It has been classified as Near Threatened on the IUCN Red List in 2015. Two subspecies are extinct, two are endangered, and two are near threatened; its status in China is not well known.
Etymology The first part of the scientific name derives from the Latin word equus which means horse and the second part from the Ancient Greek ἡμίονος, hēmíonos, from ἡμι-, hēmi-, 'half', and ὄνος, ónos, 'donkey'; thus, 'half-donkey' or mule. The term onager comes from the ancient Greek ὄναγρος, again from ὄνος, ónos, 'donkey', and ἄγριος, ágrios, 'wild'. The species was commonly known as Asian wild ass, in which case the term onager was reserved for the subspecies E. h. onager, more specifically known as the Persian onager. More recently, the species share the same name, onager.
Taxonomy and evolution
The onager is a member of the subgenus Asinus, belonging to the genus Equus and is classified under the family Equidae. The species was described and given its binomial name Equus hemionus by the German zoologist Peter Simon Pallas in 1775. 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.
Subspecies Six subspecies of the onager are widely accepted:
A seventh 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 2025, four living subspecies and two extinct subspecies of the Asiatic wild ass have been accepted. The Persian onager was formerly known as Equus onager, as it was thought to be a distinct species.
Characteristics
The onager is generally reddish-brown during the summer, becoming yellowish-brown or greyish-brown in the winter. It has a black stripe bordered in white that extends down the middle of the back. The belly, the rump, and the muzzle are white, except for the Mongolian wild ass that has a broad black dorsal stripe bordered with white. It is about 200 to 260 kg (440 to 570 lb) in size and 2.1 to 2.5 m (6 ft 11 in to 8 ft 2 in) in head-body length. Male onagers are usually larger than females.
Evolution
The genus Equus, which includes all extant equines, is believed to have evolved from Dinohippus via the intermediate form Plesippus. One of the oldest species is Equus simplicidens, described as zebra-like with a donkey-shaped head. The oldest fossil to date is about 3.5 million years old from Idaho, USA. The genus appears to have spread quickly into the Old World, with the similarly aged Equus livenzovensis documented from western Europe and Russia. Molecular phylogenies indicate the most recent common 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 diverged about 4.8 (3.2–6.5) Mya.
Distribution and habitat
The onagers' favoured habitats consist of desert plains, semideserts, oases, arid grasslands, savannahs, shrublands, steppes, mountainous steppes, and mountain ranges. The Turkmenian kulan and Mongolian wild asses are known to live in hot and colder deserts. The IUCN estimates about 28,000 mature individuals in total remain in the wild. During the late Pleistocene era around 40,000 years ago, the Asiatic wild ass ranged widely across Europe and in southwestern to northeastern Asia. It is also known from Middle Pleistocene fossils from the Nefud Desert of Saudi Arabia. The onager is regionally extinct in Israel, Saudi Arabia, Iraq, Jordan, Syria, and southern regions of Siberia.
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