rhinoceros

A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species of the superfamily Rhinocerotoidea.) Two of the extant species are native to Africa, and three to South and Southeast Asia.

Rhinoceroses are some of the largest remaining megafauna: all weigh at least one tonne in adulthood. They have a herbivorous diet, small brains (400–600 g) for mammals of their size, one or two horns, and a thick (1.5–5 cm), protective skin formed from layers of collagen positioned in a lattice structure. They generally eat leafy material, although their ability to ferment food in their hindgut allows them to subsist on more fibrous plant matter when necessary. Unlike other perissodactyls, the two African species of rhinoceros lack teeth at the front of their mouths; they rely instead on their lips to pluck food.

Rhinoceros are killed by poachers for their horns, which are bought and sold on the black market for high prices, leading to most living rhinoceros species being considered endangered. The contemporary market for rhino horn is overwhelmingly driven by China and Vietnam, where it is bought by wealthy consumers to use in traditional Chinese medicine, among other uses. Rhino horns are made of keratin, the same material as hair and fingernails, and there is no good evidence of any health benefits. A market also exists for rhino horn dagger handles in Yemen, which was the major source of demand for rhino horn in the 1970s and 1980s.

Taxonomy and naming

The word ''rhinoceros'' is derived through Latin from the grc, ῥῑνόκερως, which is composed of (''rhino-'', "nose") and (''keras'', " horn") with a horn on the nose. The plural in English is ''rhinoceros'' or ''rhinoceroses''. The collective noun for a group of rhinoceroses is ''crash'' or ''herd''. The name has been in use since the 14th century.

The family Rhinocerotidae consists of only four extant genera: '' Ceratotherium'' (white rhinoceros), '' Diceros'' (black rhinoceros), '' Dicerorhinus'' (Sumatran rhinoceros), and ''Rhinoceros'' (Indian and Javan rhinoceros). The living species fall into three categories. The two African species, the white rhinoceros and the black rhinoceros, belong to the tribe Dicerotini, which originated in the middle Miocene, about 14.2 million years ago. The species diverged during the early Pliocene and the Javan rhinoceros, which diverged from one another about 10 million years ago. The Sumatran rhinoceros is the only surviving representative of the Dicerorhinini.

A subspecific hybrid white rhino (''Ceratotherium s. simum'' × ''C. s. cottoni'') was bred at the Dvůr Králové Zoo (Zoological Garden Dvur Kralove nad Labem) in the Czech Republic in 1977. Interspecific hybridisation of black and white rhinoceros has also been confirmed.

While the black rhinoceros has 84 chromosomes (diploid number, 2N, per cell), all other rhinoceros species have 82 chromosomes. Chromosomal polymorphism might lead to varying chromosome counts. For instance, in a study there were three northern white rhinoceroses with 81 chromosomes.

Species

White

There are two subspecies of white rhinoceros: 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. The northern subspecies is critically endangered, with all that is known to remain being two captive females. There is no conclusive explanation of the name "white rhinoceros". A popular idea that "white" is a distortion of either the Afrikaans word ''wyd'' or the Dutch word ''wijd'' (or its other possible spellings ''whyde'', ''weit'', etc.,), meaning "wide" and referring to the rhino's square lips, is not supported by linguistic studies.

The white rhino has an immense body and large head, a short neck and broad chest. Females weigh and males . The head-and-body length is and the shoulder height is . On its snout it has two horns. The front horn is larger than the other horn and averages in length and can reach . The white rhinoceros also has a prominent muscular hump that supports its relatively large head. The colour 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 the distinctive flat broad mouth that is used for grazing.

Black

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 truly 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 occidentalis'') 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.

An adult black rhinoceros stands high at the shoulder and is in length. An adult weighs from , exceptionally to , with the females being smaller than the males. Two horns on the skull are made of keratin with the larger front horn typically 50 cm long, exceptionally up to 140 cm. Sometimes, a third smaller horn may develop. The black rhino is much smaller than the white rhino, and has a pointed mouth, which it uses to grasp leaves and twigs when feeding.

During the latter half of the 20th century, their numbers were severely reduced from an estimated 70,000 in the late 1960s to a record low of 2,410 in 1995. Since then, numbers have been steadily increasing at a continental level with numbers doubling to 4,880 by the end of 2010. As of 2008, the numbers are still 90% lower than three generations ago.

Indian

The Indian rhinoceros, or greater one-horned rhinoceros, (''Rhinoceros unicornis'') has a single horn 20 to 60 cm long. It is nearly as large as the African white rhino. Its thick, silver-brown skin folds into the shoulder, back, and rump, giving it an armored appearance. Its upper legs and shoulders are covered in wart-like bumps, and it has very little body hair. Grown males are larger than females in the wild, weighing from . Shoulder height is . Females weigh about and are long. The record-sized specimen was approximately .

Indian rhinos once inhabited many areas ranging from Pakistan to Myanmar and maybe even parts of China. Because of humans, they now exist in only several protected areas of India (in Assam, West Bengal, and a few pairs in Uttar Pradesh) and Nepal, plus a pair in Lal Suhanra National Park in Pakistan reintroduced there from Nepal. They are confined to the tall grasslands and forests in the foothills of the Himalayas. Two-thirds of the world's Indian rhinoceroses are now confined to the Kaziranga National Park situated in the Golaghat district of Assam, India.

Javan

The Javan rhinoceros (''Rhinoceros sondaicus'') is one of the most endangered large mammals in the world. According to 2015 estimates, only about 60 remain, in Java, Indonesia, all in the wild. It is also the least known rhino species. Like the closely related, and larger, Indian rhinoceros, the Javan rhino has a single horn. Its hairless, hazy gray skin falls into folds into the shoulder, back, and rump, giving it an armored appearance. Its length reaches including the head, and its height . Adults are variously reported to weigh 900–1,400 kg or 1,360–2,000 kg.Rhino Guide
Javan Rhinoceros
/ref> Male horns can reach 26 cm in length, while in females they are knobs or altogether absent. These animals prefer dense lowland rain forest, tall grass and reed beds that are plentiful with large floodplains and mud wallows.

Though once widespread throughout Asia, by the 1930s they were nearly hunted to extinction in Nepal, India, Burma, Peninsular Malaysia, and Sumatra for the supposed medical powers of their horns and blood. As of 2015, only 58–61 individuals remain in Ujung Kulon National Park, Java, Indonesia. The last known Javan rhino in Vietnam was reportedly killed for its horn in 2011 by Vietnamese poachers. Now only Java contains the last Javan rhinos.

Sumatran

The Sumatran rhinoceros (''Dicerorhinus sumatrensis'') is the smallest extant rhinoceros species, as well as the one with the most hair. It can be found at very high altitudes in Borneo and Sumatra. Due to habitat loss and poaching, their numbers have declined and it has become the second most threatened rhinoceros. About 275 Sumatran rhinos are believed to remain. There are three subspecies of Sumatran rhinoceros: the Sumatran rhinoceros proper (''Dicerorhinus sumatrensis sumatrensis''), the Bornean rhinoceros (''Dicerorhinus sumatrensis harrissoni'') and the possibly extinct Northern Sumatran rhinoceros (''Dicerorhinus sumatrensis lasiotis'').

A mature rhino typically stands about high at the shoulder, has a length of and weighs around , though the largest individuals have been known to weigh as much as . Like the African species, it has two horns; the larger is the front (), with the smaller usually less than long. Males have much larger horns than the females. Hair can range from dense (the densest hair in young calves) to sparse. The color of these rhinos is reddish brown. The body is short and has stubby legs. The lip is prehensile.

Sumatran rhinoceros are on the verge of extinction due to loss of habitat and illegal hunting. Once they were spread across South-east Asia, but now they are confined to several parts of Indonesia and Malaysia due to reproductive isolation. There were 320 ''D. sumatrensis'' in 1995, which by 2011 have dwindled to 216. It has been found through DNA comparison that the Sumatran rhinoceros is the most ancient extant rhinoceros and related to the extinct Eurasian woolly rhino species, ''Coelodonta''. In 1994 Alan Rabinowitz publicly denounced governments, non-governmental organizations, and other institutions for lacking in their attempts to conserve the Sumatran rhinoceros. To conserve it, they would have to relocate them from small forests to breeding programs that could monitor their breeding success. To boost reproduction, the Malaysian and Indonesian governments could also agree to exchange the gametes of the Sumatran and (smaller) Bornean subspecies. The Indonesian and Malaysian governments have also proposed a single management unit for these two ancient subspecies.

Plantations for palm oil have taken out the living areas and led to the eradication of the rhino in Sumatra.

Evolution

Rhinocerotoids diverged from other perissodactyls by the early Eocene. Fossils of '' Hyrachyus eximus'' found in North America date to this period. This small hornless ancestor resembled a tapir or small horse more than a rhino. Four families, sometimes grouped together as the superfamily Rhinocerotoidea, evolved in the late Eocene, namely the Hyracodontidae, Amynodontidae, Paraceratheriidae and Rhinocerotidae.

Hyracodontidae

Hyracodontidae, also known as "running rhinos", showed adaptations for speed, and would have looked more like horses than modern rhinos. The smallest hyracodontids were dog-sized. Hyracodontids spread across Eurasia from the mid-Eocene to early Oligocene.

Amynodontidae

The Amynodontidae, also known as "aquatic rhinos", dispersed across North America and Eurasia, from the late Eocene to early Oligocene. The amynodontids were hippopotamus-like in their ecology and appearance, inhabiting rivers and lakes, and sharing many of the same adaptations to aquatic life as hippos.

Paraceratheriidae

The Paraceratheriidae, also known as paraceratheres or indricotheres, originated in the Eocene epoch and lived until the early Miocene. The first paraceratheres were only about the size of large dogs, growing progressively larger in the late Eocene and Oligocene. The largest genus of the family was ''Paraceratherium'', which was more than twice as heavy as a bull African elephant, and was one of the largest land mammals that ever lived.

Rhinocerotidae

The family of all modern rhinoceros, the Rhinocerotidae, first appeared in the Late Eocene in Eurasia. The earliest members of Rhinocerotidae were small and numerous; at least 26 genera lived in Eurasia and North America until a wave of extinctions in the middle Oligocene wiped out most of the smaller species. Several independent lineages survived. '' Menoceras'', a pig-sized rhinoceros, had two horns side by side. The North American '' Teleoceras'' had short legs, a barrel chest and lived until about five million years ago. The last rhinos in the Americas became extinct during the Pliocene during the Miocene. Alongside the extant species, four additional species of rhinoceros survived into the Last Glacial Period: the woolly rhinoceros (''Coelodonta antiquitatis''), ''