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Zebras are several species of African equids (horse family) united by their distinctive black and white stripes. Their stripes come in different patterns unique to each individual. They are generally social animals that live in small harems to large herds. Unlike their closest relatives, horses and asses, zebras have never been truly domesticated.
There are three species of zebras: the plains zebra, the Grévy’s zebra and the mountain zebra. The plains zebra and the mountain zebra belong to the subgenus Hippotigris, but Grevy’s zebra is the sole species of subgenus Dolichohippus. The latter resembles an ass, to which it is closely related, while the former two are more horse-like. All three belong to the genus Equus, along with other living equids.
The unique stripes of zebras make these among the animals most familiar to people. They occur in a variety of habitats, such as grasslands, savannas, woodlands, thorny scrublands, mountains, and coastal hills. However, various anthropogenic factors have had a severe impact on zebra populations, in particular hunting for skins and habitat destruction. Grevy’s zebra and the mountain zebra are endangered. While plains zebras are much more plentiful, one subspecies, the quagga, went extinct in the late 19th century, though they have now been rebred from zebra DNA.
Zebras evolved among the Old World horses within the last 4 million years. Grevy’s zebras (and perhaps also Mountain Zebras) are with asses and donkeys in a separate lineage from the other zebra lineages. This means either that striped equids evolved more than once, or that common ancestors of zebras and asses were striped and only zebras retained the stripes. Extensive stripes are posited to have been of little use to equids that live in low densities in deserts (like asses and some horses) or ones that live in colder climates with shaggy coats and annual shading (like some horses).
Fossils of an ancient equid were discovered in the Hagerman Fossil Beds National Monument in Hagerman, Idaho. It was named the Hagerman horse with a scientific name of Equus simplicidens. It is believed to have been similar to the Grevy’s zebra. The animals had stocky zebra-like bodies and short, narrow, donkey-like skulls. Grevy’s zebra also has a donkey-like skull. The Hagerman horse is also called the American zebra or Hagerman zebra.