The rhinoceros family is characterized by its large size (one of the largest remaining megafauna alive today), with all of the species able to reach one ton or more in weight; herbivorous diet; and 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 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.
The rhino is killed by humans for its horn. The horns of a rhinoceros 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. Rhinoceroses have acute hearing and sense of smell, but poor eyesight. Most live to be about 60 years old or more.
These White Rhinoceros are actually gray. The White in this species' name is from the Dutch word wijd which means wide. It refers to the White Rhinoceros's wide lip compared to the Black Rhinoceros's pointed lip. The original meaning was subsequently lost in translation.
The White or Square-lipped Rhinoceros (Ceratotherium simum) is, after the elephant, the most massive remaining land animal in the world, along with the Indian Rhinoceros and the hippopotamus, which are of comparable size. There are two subspecies of White Rhinos; as of 2005, South Africa has the most of the first subspecies, the Southern White Rhinoceros (Ceratotherium simum simum). The population of Southern White Rhinos is about 14,500, making them the most abundant subspecies of rhino in the world. However, the population of the second subspecies, the critically-endangered Northern White Rhinoceros (Ceratotherium simum cottoni), is down to as few as four individuals in the wild, and as of June 2008 this sub-species are thought to have become extinct in the wild.. Six are known to be held in captivity, two of which reside in a zoo in San Diego. There are currently four that were in held in captivity since 1982 in a zoo in the Czech Republic which were transferred to a wildlife refuge in Kenya in December 2009, in an effort have the animals reproduce and save the subspecies.
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 4,600 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 which is used for grazing. White rhinos aren't actually white, they are named after the Dutch word for wide.
The Black Rhinoceros has a beak shaped lip. The Black Rhinoceros is similar in color to the White Rhinoceros
The name Black Rhinoceros (Diceros bicornis) was chosen to distinguish this species from the White Rhinoceros (Ceratotherium simum). This can be confusing, as those two species are not really distinguishable by colour. 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 tentatively declared extinct in 2006.
An adult Black Rhinoceros stands 150–175 cm (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 they use to grasp leaves and twigs when feeding.