…commonly abbreviated to rhino, is one of any five extant species of odd-toed ungulates in the family Rhinocerotidae, as well as any of the numerous extinct species therein. Two of the extant species are native to Africa and three to Southern Asia. The term "rhinoceros" is often more broadly applied to now extinct species of the superfamily Rhinocerotoidea.

Members of the rhinoceros family are some of the largest remaining megafauna, with all species able to reach or exceed one tonne in weight. 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, relying instead on their lips to pluck food.

Rhinoceros are killed by some humans for their horns, which are bought and sold on the black market, and used by some cultures for ornaments or traditional medicine. East Asia, specifically Vietnam, is the largest market for rhino horns. By weight, rhino horns cost as much as gold on the black market. People grind up the horns and consume them, believing the dust has therapeutic properties. The horns are made of keratin, the same type of protein that makes up hair and fingernails.[4] Both African species and the Sumatran rhinoceros have two horns, while the Indian and Javan rhinoceros have a single horn. The IUCN Red List identifies the Black, Javan, and Sumatran rhinoceros as critically endangered.

Source: Wikipedia