Two of the five rhinoceros species are African and three Asian. The African species have two horns, one behind the other, and their skins are gray and smooth rather than folded. The black rhinoceros, Diceros bicornis, of E and S Africa, has declined in numbers from about 65,000 in 1970 to 3,600 in 2004 (a total that represents an increase from the mid-1990s low of 2,400); the subspecies once found in W Africa is apparently extinct. At the beginning of the 20th cent. there were 2 to 3 million black rhinoceroses. The black rhinoceros has a grasping upper lip, used for browsing shrubbery. Its front horn may be over 18 in. (45 cm) long. Unpredictable and sometimes dangerous, it can turn and charge with great force if irritated. The white, or square-lipped, rhinoceros, Ceratotherium simum, is divided into two subspecies: the northern white rhinoceros, which may be extinct in the wild, and the southern white rhinoceros, which is found primarily in South Africa; the term white may be a corruption of the Afrikaans word for "wide," referring to its broad snout. The white rhinoceros is second in size among land mammals to the elephant. It stands 61/2 ft (2 m) at the shoulder, is 13 ft (4 m) long, and weighs 3 to 4 tons (2,700–3,600 kg). More than half of the world's remaining rhinoceroses are of the southern white subspecies.
Two of the Asian species have a single horn. The Indian rhinoceros, Rhinoceros unicornis, is the second largest rhinoceros and can weigh over 2 tons (1,820 kg). Its thick hide is deeply creased in places, creating the impression of armor plates; folds of thinner skin allow body movement and flexibility. Indian rhinos have reached speeds of 30 mph (48 kph) in charges. Perhaps 2,000 live on the grassy plains of Bengal, Assam, and Nepal, some of them in groups. Their population hit a low point in 1970 at 900. The solitary and smaller Javan rhinoceros, R. sondaicus, is nearly extinct. The Sumatran rhinoceros, Dicerorhinus sumatrensis, also critically endangered, is the only rhinoceros with a hairy coat and the only Asian species with two horns. Smallest of the rhinoceroses, it stands 41/2 ft (1.4 m) and weighs about 1 ton (900 kg). Fewer than 400 survive in remote forests of Sumatra, the Malay Peninsula, and Borneo.
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