Rhinoceros, often abbreviated as rhino, is a group of five extant species of odd-toed ungulates in the family Rhinocerotidae. Two of these species are native to Africa.
Members of the rhinoceros family are characterized by their large size (they are some of the largest remaining megafauna, with all of the species able to reach one tonne or more in weight); as well as by an herbivorous diet; a thick protective skin, 1.5 to 5 cm thick, formed from layers of collagen positioned in a lattice structure; relatively small brains for mammals this size (400 to 600 g); and a large horn. They generally eat leafy material, although their ability to ferment food in their hindgut allows them to subsist on more fibrous plant matter, if necessary. Unlike other perissodactyls, the two African species of rhinoceros lack teeth at the front of their mouths, relying instead on their lips to pluck food.
There are two subspecies of white rhino: the southern white rhinoceros (Ceratotherium simum simum) and the northern white rhinoceros (Ceratotherium simum cottoni). As of 2013, the southern subspecies has a wild population of 20,405 – making them the most abundant rhino subspecies in the world. However, the northern subspecies was critically endangered, with as few as four individuals in the wild; the possibility of complete extinction in the wild having been noted since June 2008.
The white rhino has an immense body and large head, a short neck and broad chest. Females weigh 1,600 kg (4,000 lb) and males 2,400 kg (5,000 lb). The head-and-body length is 3.5 to 4.6 m (11 to 15 ft) and the shoulder height is 1.8 to 2 m (5.9 to 6.6 ft). On its snout, it has two horns. The front horn is larger than the other horn and averages 90 cm (35 in) in length and can reach 150 cm (59 in). The white rhinoceros also has a prominent muscular hump that supports its relatively large head. The color of this animal can range from yellowish brown to slate grey. Most of its body hair is found on the ear fringes and tail bristles, with the rest distributed rather sparsely over the rest of the body. White rhinos have a distinctive flat broad mouth that is used for grazing.
The name black rhinoceros (Diceros bicornis) was chosen to distinguish this species from the white rhinoceros (Ceratotherium simum). This can be confusing, as the two species are not really distinguishable by color. There are four subspecies of black rhino: South-central (Diceros bicornis minor), the most numerous, which once ranged from central Tanzania south through Zambia, Zimbabwe and Mozambique to northern and eastern South Africa; South-western (Diceros bicornis bicornis), which are better adapted to the arid and semi-arid savannas of Namibia, southern Angola, western Botswana and western South Africa; East African (Diceros bicornis michaeli), primarily in Tanzania; and West African (Diceros bicornis longipes), which was declared extinct in November 2011. The native Tswanan name keitloa describes a South African variation of the black rhino in which the posterior horn is equal to or longer than the anterior horn.