The plains zebra (Equus quagga, formerly Equus burchellii), also known as the common zebra, is the most common and geographically widespread species of zebra. Its range is fragmented, but spans much of southern and eastern Africa south of the Sahara. Six or seven subspecies have been recognised, including the extinct quagga which was thought to be a separate species. More recent research supports variations in zebra populations being clines rather than subspecies. Plains zebras are intermediate in size between the larger Grévy's zebra and the smaller mountain zebra and tend to have broader stripes than both. Great variation in coat patterns exists between clines and individuals. The plain zebra's habitat is generally, but not exclusively, treeless grasslands and savanna woodlands, both tropical and temperate. They generally avoid desert, dense rainforest and permanent wetlands. Zebras are preyed upon by lions and spotted hyenas, Nile crocodiles and, to a lesser extent, leopards, cheetahs and African wild dogs. Plains zebras are a highly social species, forming harems with a single stallion, several mares and their recent offspring; bachelor groups also form. Groups may come together to form herds. The animals keep watch for predators; they bark or snort when they see a predator and the harem stallion attacks predators to defend his harem. The plains zebra remains common in game reserves, but is threatened by human activities such as hunting for its meat and hide, as well as competition with livestock and encroachment by farming on much of its habitat, and is listed as near threatened by the IUCN as of 2016. The species population is stable and not endangered, though populations in most countries have declined sharply. Taxonomy The plains zebra was formally classified by British zoologist John Edward Gray in 1824 as Equus burchellii. After the quagga, described by Pieter Boddaert in 1785, was found to be the same species in the 21st century, the plains zebra was reclassified as Equus quagga due to the principle of priority. The plains zebra and mountain zebra were traditionally placed in the subgenus Hippotigris, in contrast to Grévy's zebra, which was considered the sole species of the subgenus Dolichohippus; however, recent (2013) phylogenetic evidence finds that plains zebras are more closely related to Grévy's zebras than mountain zebras. Groves and Bell (2004) place all three species in the subgenus Hippotigris, and zebras appear to be a monophyletic lineage. In areas where plains zebras are