Temporal range: Eocene–Recent
|Black rhinoceros (Diceros bicornis) at the Saint Louis Zoo|
Members of the rhinoceros family are characterized by their large size (they are some of the largest remaining megafauna, with all of the species able to reach one tonne or more in weight); as well as by a herbivorous diet; a thick protective skin, 1.5–5 cm thick, formed from layers of collagen positioned in a lattice structure; relatively small brains for mammals this size (400–600 g); and a large horn. They generally eat leafy material, although their ability to ferment food in their hindgut allows them to subsist on more fibrous plant matter, if necessary. Unlike other perissodactyls, the two African species of rhinoceros lack teeth at the front of their mouths, relying instead on their powerful premolar and molar teeth to grind up plant food.
Rhinoceros are killed by humans for their horns, which are bought and sold on the black market, and which are used by some cultures for ornamental or traditional medicinal purposes. The horns are made of keratin, the same type of protein that makes up hair and fingernails. Both African species and the Sumatran rhinoceros have two horns, while the Indian and Javan rhinoceros have a single horn.
Taxonomy and naming
The word rhinoceros is derived through Latin from the Ancient Greek: ῥῑνόκερως, which is composed of ῥῑνο- (rhino-, "nose") and κέρας (keras, "horn"). The plural in English is rhinoceros or rhinoceroses. The collective noun for a group of rhinoceroses is crash or herd.
The five living species fall into three categories. The two African species, the white rhinoceros and the black rhinoceros, belong to the Dicerotini group, which originated in the middle Miocene, about 14.2 million years ago. The species diverged during the early Pliocene (about 5 million years ago). The main difference between black and white rhinos is the shape of their mouths - white rhinos have broad flat lips for grazing, whereas black rhinos have long pointed lips for eating foliage.
There are two living Rhinocerotini species, the Indian rhinoceros and the Javan rhinoceros, which diverged from one another about 10 million years ago. The Sumatran rhinoceros is the only surviving representative of the most primitive group, the Dicerorhinini, which emerged in the Miocene (about 20 million years ago). The extinct woolly rhinoceros of northern Europe and Asia was also a member of this tribe.
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.
There are two subspecies of white rhino: the southern white rhinoceros (Ceratotherium simum simum) and the northern white rhinoceros (Ceratotherium simum cottoni). In 2007, the southern subspecies had a wild population of 17,480 (IUCN2008) - 16,266 of which were in South Africa - making them the most abundant rhino subspecies in the world. However, the northern subspecies was critically endangered, with as few as four individuals in the wild; the possibility of complete extinction in the wild having been noted since June 2008. Six are known to be held in captivity, two of which reside at the San Diego Zoo Safari Park. Four born in a zoo in the Czech Republic were transferred to a wildlife refuge in Kenya in December 2009, in an effort to have the animals reproduce and save the subspecies.
There is no conclusive explanation of the name white rhinoceros. A popular theory 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. This rhino can exceed 3,500 kg (7,700 lb), have a head-and-body length of 3.5–4.6 m (11–15 ft) and a shoulder height of 1.8–2 m (5.9–6.6 ft). The record-sized white rhinoceros was about 4,500 kg (10,000 lb). On its snout it has two horns. The front horn is larger than the other horn and averages 90 cm (35 in) in length and can reach 150 cm (59 in). 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.
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 really 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 bicornis) 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 1.50–1.75 m (59–69 in) high at the shoulder and is 3.5–3.9 m (11–13 ft) in length. An adult weighs from 850 to 1,600 kg (1,900 to 3,500 lb), exceptionally to 1,800 kg (4,000 lb), 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.
The Indian rhinoceros, or greater one-horned rhinoceros, (Rhinoceros unicornis) has a single horn 20 to 100 cm long. Its size is comparable to that of the white rhino in Africa. Its thick, silver-brown skin forms huge folds all over its body. 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 2,500–3,200 kg (5,500–7,100 lb). Shoulder height is 1.75–2.0 m (5.75–6.5 ft). Females weigh about 1,900 kg and are 3–4 m long. The record-sized specimen was approximately 3,800 kg.
Indian rhinos once inhabited many areas ranging from Pakistan to Burma and maybe even parts of China. However, because of human influence, they now only exist in several protected areas of India (in Assam, West Bengal, and a few pairs in Uttar Pradesh) and Nepal, plus a few pairs in Lal Suhanra National Park in Pakistan. It is 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.
The Javan rhinoceros (Rhinoceros sondaicus) is one of the most endangered large mammals in the world. According to 2002 estimates, only about 60 remain, in Java (Indonesia) and Vietnam. 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 3.1–3.2 m (10–10 ft) including the head, and its height 1.5–1.7 m (4 ft 10 in–5 ft 7 in). Adults are variously reported to weigh 900–1,400 kg or 1,360–2,000 kg. 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 India, Burma, Peninsular Malaysia, and Sumatra for the supposed medical powers of their horns and blood. As of 2009, only 40 remain in Ujung Kulon Conservation, Java, Indonesia. The last rhino in Vietnam was reportedly killed in 2010.
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, its numbers have declined and it is the most threatened rhinoceros. About 275 Sumatran rhinos are believed to remain.
A mature rhino typically stands about 1.3 m (4 ft 3 in) high at the shoulder, has a length of 2.4–3.2 m (7 ft 10 in–10 ft 6 in) and weighs around 700 kg (1,500 lb), though the largest individuals have been known to weigh as much as 1,000 kilograms. Like the African species, it has two horns; the larger is the front (25–79 cm), with the smaller usually less than 10 cm long. Males have much larger horns than the females. Hair can range from dense (the densest hair in young calves) to scarce. The color of these rhinos is reddish brown. The body is short and has stubby legs. The lip is prehensile.
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. Three families, sometimes grouped together as the superfamily Rhinocerotoidea, evolved in the late Eocene: Hyracodontidae, Amynodontidae and Rhinocerotidae.
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; the largest was Indricotherium, believed to be one of the largest land mammals that ever existed. The hornless Indricotherium was almost seven metres high, ten metres long, and weighed as much as 15 tons. Like a giraffe, it ate leaves from trees. The hyracodontids spread across Eurasia from the mid-Eocene to early Miocene.
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.
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. However, 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 5 million years ago. The last rhinos in the Americas became extinct during the Pliocene.
Modern rhinos are believed to have begun dispersal from Asia during the Miocene. Two species survived the most recent period of glaciation and inhabited Europe as recently as 10,000 years ago: the woolly rhinoceros and Elasmotherium. The woolly rhinoceros appeared in China around 1 million years ago and first arrived in Europe around 600,000 years ago. It reappeared 200,000 years ago, alongside the woolly mammoth, and became numerous. Eventually it was hunted to extinction by early humans. Elasmotherium, also known as the giant rhinoceros, survived through the middle Pleistocene: it was two meters tall, five meters long and weighed around five tons, with a single enormous horn, hypsodont teeth and long legs for running.
Of the extant rhinoceros species, the Sumatran rhino is the most archaic, first emerging more than 15 million years ago. The Sumatran rhino was closely related to the woolly rhinoceros, but not to the other modern species. The Indian rhino and Javan rhino are closely related and form a more recent lineage of Asian rhino. The ancestors of early Indian and Javan rhino diverged 2–4 million years ago.
The origin of the two living African rhinos can be traced to the late Miocene ( ) species Ceratotherium neumayri. The lineages containing the living species diverged by the early Pliocene ( ), when Diceros praecox, the likely ancestor of the black rhinoceros, appears in the fossil record. The black and white rhinoceros remain so closely related that they can still mate and successfully produce offspring.
- Family Rhinocerotidae
- Subfamily Rhinocerotinae
- Tribe Aceratheriini
- †Aceratherium lived from 33.9—3.4 Ma
- †Acerorhinus 13.6—7.0 Ma
- †Alicornops 13.7—5.33 Ma
- †Aphelops 20.430—5.330 Ma
- †Chilotheridium 23.03—11.610 Ma
- †Chilotherium 13.7—3.4 Ma
- †Dromoceratherium 15.97—7.25 Ma
- †Floridaceras 20.43—16.3 Ma
- †Hoploaceratherium 16.9—16.0 Ma
- †Peraceras 20.6—10.3 Ma
- †Plesiaceratherium 20.0—11.6 Ma
- †Proaceratherium 16.9—16.0 Ma
- Tribe Teleoceratini
- Tribe Rhinocerotini 40.4—11.1 Ma—Present
- Tribe Dicerorhinini
- Tribe Dicerotini 23.03—Present
- Tribe Aceratheriini
- Subfamily Elasmotheriinae
- †Gulfoceras 23.030—20.430 Ma
- Tribe Diceratheriini
- Tribe Elasmotheriini 20.0—0.126 Ma
- †Bugtirhinus 20.0—16.9 Ma
- †Elasmotherium – Giant rhinoceros 3.6—0.126 Ma
- †Hispanotherium synonymized with Huaqingtherium 16.0—7.250 Ma
- †Menoceras 23.03—16.3 Ma
- †Ougandatherium 20.0—16.9 Ma
- †Sinotherium 9.0—5.3 Ma
- Subfamily Rhinocerotinae
In the wild, adult rhinoceros have no real natural predators other than humans. Young rhinos can fall prey to predators such as big cats, crocodiles, wild dogs, and hyenas. Although rhinos are large and have a reputation for being tough, they are very easily poached; they visit water holes daily and can be easily killed while they drink. As of December 2009, poaching increased globally while efforts to protect the rhino are considered increasingly ineffective. The worst estimate, that only 3% of poachers are successfully countered, is reported of Zimbabwe. The market for rhino horn is largely supported by practitioners of traditional Chinese medicine which considers the horn effective medicine against fever and even "life saving". Apparently, only Nepal has avoided the crisis, while poachers become more sophisticated. South African officials have called for urgent action against poaching after poachers killed the last female rhino in the Krugersdorp Game Reserve near Johannesburg. Statistics from South African National Parks show a record 333 rhinoceros were killed in 2010. This increased to 668 in 2012.
Rhinoceros horns, unlike those of other horned mammals (which have a bony core), only consist of keratin. Rhinoceros horns are used in traditional Asian medicine, and for dagger handles in Yemen and Oman. Esmond Bradley Martin has reported on the trade for dagger handles in Yemen.
One repeated misconception is that rhinoceros horn in powdered form is used as an aphrodisiac in Traditional Chinese Medicine (TCM) as Cornu Rhinoceri Asiatici (犀角, xījiǎo, "rhinoceros horn"). In fact, it is prescribed for fevers and convulsions. Neither have been proven by evidence-based medicine. Discussions with TCM practitioners to reduce its use have met with mixed results because some TCM doctors consider rhino horn a life-saving medicine of better quality than substitutes. China has signed the CITES treaty and removed rhinoceros horn from the Chinese medicine pharmacopeia, administered by the Ministry of Health, in 1993. In 2011, in the United Kingdom, the Register of Chinese Herbal Medicine issued a formal statement condemning the use of rhinoceros horn. A growing number of TCM educators have also spoken out against the practice.
To prevent poaching, in certain areas, rhinos have been tranquilized and their horns removed. Armed park rangers, particularly in South Africa, are also working on the front lines to combat poaching, sometimes killing poachers who are caught in the act. A recent spike in rhino killings has made conservationists concerned about the future of the species. During 2011, 448 rhino were killed for their horn in South Africa alone. The horn is incredibly valuable: an average sized horn can bring in as much as a quarter of a million dollars in Vietnam and many rhino range states have stockpiles of rhino horn.
Still, poaching is hitting record levels due to demands from China and Vietnam. In March 2013, some researchers suggested that the only way to reduce poaching would be to establish a regulated trade based on humane and renewable harvesting from live rhinos.
Albrecht Dürer created a famous woodcut of a rhinoceros in 1515, based on a written description and brief sketch by an unknown artist of an Indian rhinoceros that had arrived in Lisbon earlier that year. Dürer never saw the animal itself and, as a result, Dürer's Rhinoceros is a somewhat inaccurate depiction.
There are legends about rhinoceros stamping out fire in Malaysia, India, and Burma. The mythical rhinoceros has a special name in Malay, badak api, where badak means rhinoceros and api means fire. The animal would come when a fire is lit in the forest and stamp it out. There are no recent confirmations of this phenomenon. However, this legend has been reinforced by the film The Gods Must Be Crazy, where an African rhinoceros is shown to be putting out two campfires.
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|Wikisource has the text of the 1911 Encyclopædia Britannica article rhinoceros.|
- Rhino Species & Rhino Images page on the Rhino Resource Center
- Rhinoceros entry on World Wide Fund for Nature website.
- International Anti Poaching Foundation