Black Rhinoceros

The black rhinoceros (Diceros bicornis) is one of five species of rhinoceros that compose family Rhinocerotidae, order Perissodactyla (horses, zebras, asses, tapirs, and rhinoceros). They are an important component of the unparalleled diversity of large mammalian herbivores inhabiting African savannas. This once abundant species is seriously endangered and at risk of extinction in the wild. Ancestral Rhinocerotidae are first recorded from Late Eocene sediments in the New and Old World; the family reached its greatest species-diversity during the Oligocene and Miocene.

Black rhinoceros (like all perissodactyls) are adapted for running (cursorial). Body weight is supported by the central digits, with the primary axis of the foot passing through the third digit (mesaxonic). The body is massive (weighing up to 1,400 kilograms) with short, stumpy limbs. Head and body length can reach up to 375 cm, and shoulder height up to 180 cm. Males are larger than females.

Despite its common name, the thick, scantily haired skin of black rhinoceros is not black but dark brown or dark gray with yellowish highlights (usually obscured by mud or dust). The two conical horns (a stubby third horn is sometimes present) are composed of com pressed keratin, not bone, with the longer anterior horn averaging 50 cm (the record is 135.9 cm). Females usually have longer horns than males. The upper lip has a central, prehensile protrusion. This hooked lip and the smaller size of the black rhinoceros distinguish it from the square-lipped, larger white rhinoceros. The short tail is tipped with stiff bristles.

Black rhinoceros occur in forest, savanna woodland, and scrub, and they are not usually associated with open plains. They are browsers, gathering thin, regenerating twigs of woody plants, particularly acacias. Rhinoceros feed most intensively during early morning and evening, drink daily, frequently utilize mineral licks, and sleep at midday, often in mud or water wallows. They are not found farther than about 25 km from permanent water.

Adult males are usually solitary but sometimes feed together. A temporary group (clan) forms between an adult female and her calf; this clan persists until the next calf is born. The ranges of clans often overlap, but in dense populations, breeding males occupy mutually exclusive home ranges. Alarm, threat, and contact are communicated by snorts and olfactory cues; males mark their territories by spraying urine. Breeding occurs throughout the year. A single calf is born after a gestation of up to 478 days and weaned after two years. Captive animals have lived up to forty-five years.

The natural range of D. bicornis once encompassed the savannas of northern, eastern, and southern Africa. Populations have declined from hundreds of thousands to about 3,000 individuals during the last three centuries because of predation by humans, who hunted them for their hides and horns, and converted their habitats into farmland and settlements. Most populations are critically endangered, despite intensive conservation efforts that include protection of wild populations, rein-

A black rhinoceros under 24-hour guard because of the risk of poaching, Zimbabwe (Qallo Images/Corbis)

troduction of animals into areas where the species once occurred, and captive breeding programs throughout the world.

—Mary Ellen Holden

See also: Endangered Species; Mammalia; Perisso-dactyls; Preservation of Species

Bibliography

Carroll, Robert. 1988. Vertebrate Paleontology and Evolution. New York: W. H. Freeman; Hillman Smith, A. Kes, and Colin P. Groves. 1994. "Diceros bicornis." Mammalian Species 455: 1-8; Kingdon, Jonathan. 1979. East African Mammals: An Atlas of Evolution in Africa. Vol. 3B: Large Mammals. London: Academic; Kingdon, Jonathan. 1997. The Kingdon Field Guide to African Mammals. New York: Academic; Nowak, Ronald M. 1999. Walker's Mammals of the World, 6th ed. Vol. 2. Baltimore: Johns Hopkins University Press; Smithers, Reay H. N. 1983. The Mammals of the Southern African Subregion. Pretoria, Republic of South Africa: University of Pretoria Press.

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