Which of these facts about rhinoceros is wrong?

A rhinoceros 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.

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. The horns are made of keratin, the same type of protein that makes up hair and fingernails.