The rhinoceros, or rhino, is any of five surviving species of odd-toed ungulates in the family Rhinocerotidae. Two species are native to Africa and three to southern Asia. Three of the five species are critically endangered, and another, the Indian Rhinoceros, is endangered.
The family is characterised by large size with all of the species capable of reaching one ton or more in weight; herbivorous diet; and a thick protective skin, formed from layers of collagen positioned in a lattice structure; relatively small brains for mammals this size (400-600g); and its horn. The rhino is prized for its horn. The horns of a Rhinoceros are made of keratin, the same type of protein that makes up hair, but the horn is not itself made of hair as some have believed. Rhinoceros also have acute hearing and sense of smell, but poor eyesight. Most rhinoceros live to be about 50 years old or more. The collective noun for a group of rhinoceros is "crash". Both African species and the Sumatran Rhinoceros have two horns, while the Indian and Javan Rhinoceros have a single horn.