Black Rhinoceros (Diceros Bicornis)
The black rhinoceros or hook-lipped rhinoceros (Diceros bicornis) is a species of rhinoceros, native to eastern and central Africa including Kenya, Tanzania, Cameroon, South Africa, Namibia, Zimbabwe, andAngola. Although the rhinoceros is referred to as black, its colors vary from brown to grey.
The other African rhinoceros is the white rhinoceros (Ceratotherium simum). The word “white” in the name “white rhinoceros” is a misinterpretation of the Afrikaans word wyd, itself derived from the Dutch word wijdfor wide, referring to its square upper lip, as opposed to the pointed or hooked lip of the black rhinoceros. These species are now sometimes referred to as the square-lipped (for white) or hook-lipped (for black) rhinoceros.
The species was first named Rhinoceros bicornis by Carolus Linnaeus in the 10th edition of his Systema naturae in 1758. The name means “double-horned rhinoceros”. There is some confusion about what exactly Linnaeus conceived under this name as this species was probably based upon the skull of a single-horned Indian rhinoceros (Rhinoceros unicornis), with a second horn artificially added by the collector. Such a skull is known to have existed and Linnaeus even mentioned India as origin of this species. However he also referred to reports from early travellers about a double-horned rhino in Africa and when it emerged that there is only one, single-horned species of rhino in India, “Rhinoceros” bicornis was used to refer to the African rhinos (the white rhino only became recognised in 1812). In 1911 this was formally fixed and the Cape of Good Hope officially declared the type locality of the species.
The intraspecific variation in the black rhinoceros has been discussed by various authors and is not finally settled. The most accepted scheme considers seven or eight subspecies, of which three became extinct in historical times and one is on the brink of extinction:
- Southern black rhinoceros or Cape rhinoceros (D. b. bicornis) – Extinct. Once abundant from the Cape of Good Hope to Transvaal, South Africa and probably into the south of Namibia, this was the largest subspecies. It became extinct due to excessive hunting and habitat destruction around 1850.
- North-eastern black rhinoceros (D. b. brucii) – Extinct. Formerly central Sudan, Eritrea, northern and southeastern Ethiopia, Djibouti and northern and southeastern Somalia. Relict populations in northern Somalia vanished during the early 20th century.
- Chobe black rhinoceros (D. b. chobiensis) – A local subspecies restricted to the Chobe Valley in southeastern Angola, Namibia (Zambezi Region) and northern Botswana. Nearly extinct, possibly only one surviving specimen in Botswana.
- Uganda black rhinoceros (D. b. ladoensis) – Former distribution from South Sudan, across Uganda into western Kenya and southwesternmost Ethiopia. Black rhinos are considered extinct across most of this area and its conservational status is unclear. Probably surviving in Kenyan reserves.
- Western black rhinoceros (D. b. longipes) – Extinct. Once lived in South Sudan, northern Central African Republic, southern Chad, northern Cameroon, northeastern Nigeria and south-eastern Niger. The range possibly stretched west to the Niger River in western Niger, though this is unconfirmed. The evidence from Liberia and Burkina Faso mainly rests upon the existence of indigenous names for the rhinoceros. A far greater former range in West Africa as proposed earlier is doubted by a 2004 study. The last known wild specimens lived in northern Cameroon. In 2006 an intensive survey across its putative range in Cameroon failed to locate any, leading to fears that it was extinct in the wild. On November 10, 2011 the IUCN declared the western black rhinoceros extinct.
- Eastern black rhinoceros (D. b. michaeli) – Had a historical distribution from South Sudan, Ethiopia, down through Kenya into north-central Tanzania. Today, its range is limited primarily to Tanzania.
- South-central black rhinoceros (D. b. minor) – Most widely distributed subspecies, characterised by a compact body, proportionally large head and prominent skin-folds. Ranged from north-eastern South Africa (KwaZulu-Natal) to northeastern Tanzania and southeastern Kenya. Preserved in reserves throughout most of its former range but probably extinct in eastern Angola, southern Democratic Republic of Congo and possibly Moçambique. Extinct but reintroduced in Malawi, Botswana, and Zambia.
- South-western black rhinoceros (D. b. occidentalis) – A small subspecies, adapted to survival in desert and semi-desert conditions. Originally distributed in north-western Namibia and southwestern Angola, today restricted to wildlife reserves in Namibia with sporadic sightings in Angola. These populations are often erroneously referred to D. b. bicornis or D. b. minor but represent a subspecies in their own right.
The most widely adopted alternative scheme only recognizes five subspecies or “eco-types”, D. b. bicornis, D. b. brucii, D. b. longipes, D. b. michaeli, and D. b. minor. This concept is also used by the IUCN, listing three surviving subspecies and recognizing D. b. brucii and D. b. longipes as extinct. The most important difference to the above scheme is the inclusion of the extant southwestern subspecies from Namibia in D. b. bicornis instead of in its own subspecies, whereupon the nominal subspecies is not considered extinct.
The rhinoceros originated in the Eocene about fifty million years ago alongside other ungulates (hooved animals). Ancestors of the black and the white rhinoceros were present in Africa by the end of the Late Miocene about ten million years ago. The two species evolved from the common ancestral species Ceratotherium neumayriduring this time. The clade comprising the genus Diceros is characterised by an increased adaptation to browsing. Between four and five million years ago, the black rhinoceros diverged from the white rhinoceros. After this split, the direct ancestor of Diceros bicornis, Diceros praecox was present in the Pliocene of East Africa (Ethiopia, Kenya, Tanzania). D. bicornis evolved from this species during the Late Pliocene – Early Pleistocene.
An adult black rhinoceros stands 140–180 cm (55–71 in) high at the shoulder and is 3–3.75 m (9.8–12.3 ft) in length. An adult typically weighs from 800 to 1,400 kg (1,800 to 3,100 lb), however unusually large male specimens have been reported at up to 2,199–2,896 kg (4,848–6,385 lb). The females are smaller than the males. Two horns on the skull are made of keratin with the larger front horn typically 50 cm (20 in) long, exceptionally up to 140 cm (55 in).
The longest known black rhinoceros horn measured nearly 1.5 m (4.9 ft) in length. Sometimes, a third, smaller horn may develop. These horns are used for defense, intimidation, and digging up roots and breaking branches during feeding. The black rhino is smaller than the white rhino, and is close in size to the Javan Rhino of Indonesia. It has a pointed and prehensile upper lip, which it uses to grasp leaves and twigs when feeding. The white rhinoceros has square lips used for eating grass. The black rhinoceros can also be distinguished from the white rhinoceros by its size, smaller skull, and ears; and by the position of the head, which is held higher than the white rhinoceros, since the black rhinoceros is a browser and not a grazer. This key differentiation is further illustrated by the shape of the two species mouths (lips): the “square” lip of the white rhinoceros is an adaptation for grazing, and the “hooked” lip of the black rhinoceros is an adaptation to help browsing.
Their thick-layered skin helps to protect the rhino from thorns and sharp grasses. Their skin harbors external parasites, such as mites and ticks, which may be eaten by oxpeckers and egrets. Such behaviour was originally thought to be an example of mutualism, but recent evidence suggests that oxpeckers may be parasites instead, feeding on rhino blood. Black rhinos have poor eyesight, relying more on hearing and smell. Their ears have a relatively wide rotational range to detect sounds. An excellent sense of smell alerts rhinos to the presence of predators.
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