More than 200 species of mammal are distinguished by possession of hooves, known as ungulates, and are divided into two orders, even-toed and odd-toed ungulates. The smaller order is made up of three families - horses, rhinoceroses and tapirs.
Rhinos have existed for over 50 million years. In the past there were many different kinds of rhinos, roaming North America, Europe, Africa and Asia, including the largest land mammal that ever lived.
Today, five species of rhino survive, but all are on the verge of extinction. It would be a catastrophic loss if such a venerable group of animals were to vanish from the world.
The rhinoceros is a large, ponderous, hoofed, primitive-looking mammal, found today in eastern and southern Africa and tropical Asia. They have massive bodies, large heads, three digits on both front and hind feet and thickly folded skin that forms plate-like folds resembling armour, especially at shoulders and thighs.
All rhinos are grey or brown in colour and most are nearly hairless. Rhinos may grow to 14 feet long and 6.5 feet high at shoulder. Adults may weigh up to four tons and the huge body rests on four short stumpy legs.
The name rhinoceros means "nose horn". Some species have one large horn curving upwards from the snout, while other species have two horns. The horn grows from the skin, is hard, and is made from a solid mass of hairs. Like hair, the horn grows as much as three inches per year. The longest known horn was over five feet long.
Two species of rhino live in Africa: the black rhinoceros and the white, or square-lipped, rhinoceros (both animals are grey). Both animals have two horns. Next to the elephant, the white rhinoceros ranks with the hippopotamus as the largest living land mammal. White rhinos live on grassy plains in herds of about 10 animals. The males fight a lot during the breeding season.
The black rhino is smaller than the white and adults live alone in dry inland areas along the coast and in the mountains. Rhinos are vegetarian. The white rhino grazes on dense, short green grass. The black rhino browses on trees and shrubs. Rhinos are generally promiscuous, rarely forming even semi-permanent pairings.
The other three species of rhino (Indian, Javan and Sumatran) live in Asia. Two species are one-horned (Indian, Javan) and the other is two-horned (Sumatran). The one-horned species lives in swampy jungles. The Sumatran rhino is the smallest and, unlike other species, it is hairy.
Rhinos have small eyes and are short-sighted, but their senses of hearing and smell are keen. They prefer to avoid humans, but males, particularly during the breeding season, and females with calves, may charge with very little provocation. They can run at speeds of up to 28 miles per hour for short distances and will gouge with their horns if they make contact. For all its bulk, the rhino is very agile and can turn quickly in a small space.
Rhinos use many sounds to communicate. They snort, snarl and roar, and, when fighting, they grunt and scream. Both males and females whistle when courting.
The female rhino (cow) bears a single calf every three or four years. The gestation period is 18 months and the calf weighs up to 100lbs. The calves are frisky and playful, and the cow comforts them with soft mewing noises.
The cow is fiercely defensive of the calf against predators such as crocodiles, lions and hyenas. As the older calves mature, they leave their mothers and may join other females and their young where they are tolerated for a while before departing to live independently.
The African White rhino has a symbiotic (mutually dependent) relationship with red-billed ox-peckers, also called tick birds. In Swahili, the tick bird is named "askari wa kifaru", which means "the rhino's guard". The bird eats ticks that are present on the rhino and also noisily warns the rhino of danger. Although the birds also eat blood from sores on the rhino's skin and thereby obstruct healing, they are still tolerated.
All species of rhino are threatened and some are very close to extinction. The Sumatran rhino has been exterminated in much of its range and only 400 remain. About 2,400 Indian rhino, about 10,400 White rhino, and about 2,700 Black rhino survive. The Javan rhino is one of the world's most critically endangered species, and only about 60 survive.
The above figures (14,000 in total) refer to rhinos surviving in the wild. In addition, about 1,000 rhinos are held in captivity worldwide.
IN the wild the adult rhino has no true natural predator. Man is the cause of the demise of the rhino. Despite the rhino's size and aggressive reputation, it is still very easy for hunters to kill the animal. They are creatures of habit, live in a well-defined home range and usually visit the water-hole daily where they are easily ambushed.
Despite protective laws, they continue to be hunted. Nearly all parts of the rhino are used in traditional folk medicine in Asia and the horn is valued as a knife handle in the Middle East. Many East Asian peoples believe that the rhino horn is a powerful aphrodisiac.
Most rhinos are hunted primarily for their horns. It is a particular shame to kill a great creature in order to harvest a single organ deemed desirable to humans. Apart from the rhino, elephants are killed for their tusks, buffaloes for their tongues, and gorillas because some people want to buy ashtrays made out of large primate paws.
Urgent efforts are under way to save the rhino from extinction. The Black rhino population declined greatly due to poaching in the 1970s and 1980s. Many rhinos were moved to fenced sanctuaries in the early 1990s, an effort that seems to be succeeding. In 1994 rhino numbers did not decline for the first time in 20 years.
William Reville is a senior lecturer and director of microscopy at UCC.