Zebras (US: , UK: ) (subgenus Hippotigris) are African equines with distinctive black-and-white striped coats. There are three living species: Grévy's zebra (Equus grevyi), the plains zebra (E. quagga), and the mountain zebra (E. zebra). Zebras share the genus Equus with horses and asses, the three groups being the only living members of the family Equidae. Zebra stripes come in different patterns, unique to each individual. Several theories have been proposed for the function of these patterns, with most evidence supporting them as a deterrent for biting flies. Zebras inhabit eastern and southern Africa and can be found in a variety of habitats such as savannahs, grasslands, woodlands, shrublands, and mountainous areas. Zebras are primarily grazers and can subsist on lower-quality vegetation. They are preyed on mainly by lions, and typically flee when threatened but also bite and kick. Zebra species differ in social behaviour, with plains and mountain zebra living in stable harems consisting of an adult male or stallion, several adult females or mares, and their young or foals; while Grévy's zebra live alone or in loosely associated herds. In harem-holding species, adult females mate only with their harem stallion, while male Grévy's zebras establish territories which attract females and the species is promiscuous. Zebras communicate with various vocalisations, body postures and facial expressions. Social grooming strengthens social bonds in plains and mountain zebras. Zebras' distinctive stripes make them among the most recognisable mammals. They have been featured in art and stories in Africa and beyond. Historically, they have been highly sought by exotic animal collectors, but unlike horses and donkeys, zebras have never been completely domesticated. The International Union for Conservation of Nature (IUCN) lists Grévy's zebra as endangered, the mountain zebra as vulnerable and the plains zebra as near-threatened. The quagga (E. quagga quagga), a type of plains zebra, was driven to extinction in the 19th century. Nevertheless, zebras can be found in numerous protected areas.
Etymology The English name "zebra" derives from Italian, Spanish or Portuguese. Its origins may lie in the Latin equiferus, meaning "wild horse". Equiferus appears to have entered into Portuguese as ezebro or zebro, which was originally used for a mysterious equine reported in the wilds of the Iberian Peninsula during the Middle Ages. In 1591, Italian explorer Filippo Pigafetta recorded "zebra" being used to refer to the African animals by Portuguese visitors to the continent. In ancient times, the zebra was called hippotigris ("horse tiger") by the Greeks and Romans. The word zebra was traditionally pronounced with a long initial vowel, but over the course of the 20th century the pronunciation with the short initial vowel became the norm in British English. The pronunciation with a long initial vowel remains standard in American English.
Taxonomy
Zebras are classified in the genus Equus (known as equines) along with horses and asses. These three groups are the only living members of the family Equidae. The plains zebra and mountain zebra were traditionally placed in the subgenus Hippotigris (C. H. Smith, 1841) in contrast to the Grévy's zebra which was considered the sole species of subgenus Dolichohippus (Heller, 1912). Groves and Bell (2004) placed all three species in the subgenus Hippotigris. A 2013 phylogenetic study found that the plains zebra is more closely related to Grévy's zebras than mountain zebras. The extinct quagga was originally classified as a distinct species. Later genetic studies have placed it as the same species as the plains zebra, either a subspecies or just the southernmost population. Molecular evidence supports zebras as a monophyletic lineage. Equus originated in North America and direct paleogenomic sequencing of a 700,000-year-old middle Pleistocene horse metapodial bone from Canada implies a date of 4.07 million years ago (mya) for the most recent common ancestor of the equines within a range of 4.0 to 4.5 mya. Horses split from asses and zebras around this time and equines colonised Eurasia and Africa around 2.1–3.4 mya. Zebras and asses diverged from each other close to 2 mya. The mountain zebra diverged from the other species around 1.6 mya and the plains and Grévy's zebra split 1.4 mya. A 2017 mitochondrial DNA study placed the Eurasian Equus ovodovi and the subgenus Sussemionus lineage as closer to zebras than to asses. However, other studies disputed this placement, finding the Sussemionus lineage basal to the zebra+asses group, but suggested that the Sussemionus lineage may have received gene flow from zebras. The cladogram of Equus below is based on Vilstrup and colleagues (2013) and Jónsson and colleagues (2014):
Extant species
Fossil record
In addition to the three living species, some fossil zebras and relatives have also been identified. E. oldowayensis is identified from remains in Olduvai Gorge dating to 1.8 mya. Fossil skulls of E. mauritanicus from Algeria which date to around 1 mya appears to show affinities with the plains zebra. E. capensis, known as the Cape zebra, appeared around 2 mya and lived throughout southern and eastern Africa.
Hybridisation
Fertile hybrids have been reported in the wild between plains and Grévy's zebra. Hybridisation has also been recorded between the plains and mountain zebra, though it is possible that these are infertile due to the difference in chromosome numbers between the two species. Captive zebras have been bred with horses and donkeys; these are known as zebroids. A zorse is a cross between a zebra and a horse; a zonkey, between a zebra and a donkey; and a zoni, between a zebra and a pony. Zebroids are often born sterile with dwarfism.
Characteristics
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