RHINOCEROS,
common name for any animal of the Rhinocerotidae, a family
of odd-toed ungulates characterized by one or two median horns on
the snout. The horns are composed of a mass of agglutinated keratin,
a fibrous protein found in hair; they are used mostly for digging
up bulbs that, with grass and other foliage, constitute the principal
food of the animal. The rhinoceros has a massive body and short, thick
legs. Each foot has three functional toes covered separately with
broad, hooflike nails; each forefoot also bears a nonfunctional
toe. The skin is rough and thick, gray or brown in color, and, in
the Asian species, marked by folds at the neck and limb junctures,
so that the animal appears to be covered with armor plates. The
vision of the rhinoceros is poor, but this deficiency is compensated
for by acute senses of smell and hearing.
Rhinoceroses are solitary animals that may also form small
herds when living in grassland areas. When a female is in estrus,
fighting may occur among males; the victor conducts an elaborate
courtship that includes attacks on the male by the female. The one
offspring produced, after a gestation of 15 to 18 months, may stay with
the mother for two and one-half years. Sometimes a female is seen
with two calves, one well grown and one small.
Although the rhinoceros family was widespread in older geological
times, only five species now exist: three in Asia and the Malay
Archipelago, and two in tropical Africa. The former are characterized
by incisors and canine teeth, both of which are lacking in the African
species, as well as by the armor-plate arrangement of the skin.
The Indian rhinoceros, Rhinoceros unicornis, has
a single horn and grows to a shoulder height of about 1.7 m (about
5.5 ft); it is now found only on the plains of Assam State. The
similar but smaller Javan rhinoceros, R. sondaicus, now
found only in western Java, once ranged the hilly tropical forests
of Bengal, Burma, Borneo, Java, and Sumatra. The two-horned Sumatran
rhinoceros, Dicerorhinus sumatrensis, has been widely
eliminated from a similar former range.
The African black rhinoceros, Diceros bicornis, a
two-horned species found in savannas and on mountainsides south
of Ethiopia, is characterized by a long, pointed, prehensile upper
lip; it is the only member of its family with a fairly substantial
population in the wild. The African white rhinoceros, Ceratotherium
simum, exists only in two or three game preserves. It is
the largest living land mammal except for the elephant, sometimes
growing to a shoulder height of almost 2 m (almost 7 ft) and a length
of more than 5 m (more than 16 ft).
Rhinoceroses, particularly the black rhino, have a reputation
for being dangerous, but in general they are peaceful and even timid
except when threatened; a charging rhino is then, indeed, quite
dangerous. Besides being a declining life form like other perissodactyls,
the otherwise protected rhinoceros suffers from the large market
in the Orient for its horn, which is prized as a medicine and aphrodisiac.
Because of this market, four of the five rhinoceros species are
at a point near extinction.