Description
An adult black rhinoceros stands 132–180 cm (52–71 in) high at the shoulder and is 2.8–3.8 m (9.2–12 ft) in length, plus a tail of about 60 cm (24 in) in length. An adult typically weighs from 800 to 1,400 kg (1,800 to 3,100 lb), however unusually large male specimens have been reported at up to 2,199–2,896 kg (4,850–6,380 lb). The females are smaller than the males. Two horns on the skull are made of keratin with the larger front horn typically 50 cm (20 in) long, exceptionally up to 140 cm (55 in).
The longest known black rhinoceros horn measured nearly 1.5 m (4.9 ft) in length. Sometimes, a third, smaller horn may develop. These horns are used for defense, intimidation, and digging up roots and breaking branches during feeding. The black rhino is smaller than the white rhino and has a pointed and prehensile upper lip, which it uses to grasp leaves and twigs when feeding. The white rhinoceros has square lips used for eating grass. The black rhinoceros can also be distinguished from the white rhinoceros by its size, smaller skull, and ears; and by the position of the head, which is held higher than the white rhinoceros, since the black rhinoceros is a browser and not a grazer. This key differentiation is further illustrated by the shape of the two species mouths (lips): the "square" lip of the white rhinoceros is an adaptation for grazing, and the "hooked" lip of the black rhinoceros is an adaptation to help browsing.
Their thick-layered skin protects the rhino from thorns and sharp grasses. Their skin harbors external parasites, such as mites and ticks, which are eaten by oxpeckers and egrets that live with the rhino. Such behaviour was originally thought to be an example of mutualism, but recent evidence suggests that oxpeckers may be parasites instead, feeding on rhino blood. Black rhinos have poor eyesight, relying more on hearing and smell. Their ears possess a relatively wide rotational range to detect sounds. An excellent sense of smell alerts rhinos to the presence of predators.
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