rhinoceros, massive hoofed mammal of Africa, India, and SE Asia, characterized by a snout with one or two horns. The rhinoceros family, along with the horse and tapir families, forms the order of odd-toed hoofed mammals. The five living species, which once ranged widely across Africa and Asia, now consist of remnant populations in protected or remote areas. All are listed as endangered, with the exception of one subspecies of the white rhinoceros.
The skin of the rhinoceros is extremely thick, nearly hairless in most species, and deeply folded in some. The horns, arising from the skin, are made of keratin, a fibrous substance. The legs are stout and short and end in broad feet, each with three toes. Rhinoceroses are herbivorous, browsers or grazers according to the species. Most live near water and like to wallow in mud; all swim well. They have poor vision but good hearing and a good sense of smell. Mostly solitary animals, they feed by night and in the early morning and evening; they rest in shade during the heat of the day. They are often accompanied by small tickbirds (oxpeckers) that feed on parasites in their skin and, by their cries, alert them to danger. Although most rhinoceroses are placid animals, mothers fiercely protect their offspring.
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 4,800 in 2012 (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). Some 20,000 southern white rhinoceroses survive. The vast majority of African rhinoceroses are now found in South Africa.
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.
Rhinoceroses are endangered and close to extinction due to loss of their natural habitats to expanding human settlement and agriculture, and especially because of poaching and illegal trade in rhinoceros horns. The horns are believed in Asian traditions to have aphrodisiac or healing properties. They have commanded a very high price for centuries, sometimes surpassing that of gold. Some Middle Eastern societies prize rhinoceros horn for dagger handles. Despite a ban on trade in rhinoceros parts under the Convention on International Trade in Endangered Species (CITES) in 1976, populations declined by 90% over the next 20 years. Unless poaching is stopped, rhinoceros extinction in the wild is virtually inevitable. The poaching problem, exacerbated by poverty and political unrest in many areas, has turned into a war, and dozens of poachers and wildlife sanctuary guards have lost their lives. Aggressive captive breeding programs under way for most species have met with limited success.
The rhinoceros is classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Perissodactyla, family Rhinocerotidae.
See M. Penny, Rhino (1988); S. Fitzgerald, International Wildlife Trade (1989); F. B. Salvadori, Rare Animals of the World (1990).