Odd-Toed Ungulates: Perissodactyla

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ODD-TOED UNGULATES: Perissodactyla


Ungulates (UNG-gyuh-luhts) are hoofed mammals. What makes perissodactyls (puh-RIH-suh-dack-tuhlz) different from artiodactyls (ar-tee-oh-DACK-tuhlz), is the number of toes. The presence of a single toe links the horse family (including horses, zebras, and asses), tapir, and rhinoceros together. This single toe is actually a combination of three toes that bear the weight together, with the middle toe being the largest of the three. Tapirs have four toes on the front feet and three on the back, while rhinoceroses (frequently called "rhinos") have three on all feet, and horses have just one.

The smallest perissodactyl is the mountain tapir, which weighs up to 485 pounds (220 kilograms). The white rhinoceros is the largest and can weigh more than 7,700 pounds (3,500 kilograms). Male rhinos and horses are bigger than females, but the opposite is true for tapirs.

Horses are medium sized with long heads and the ears stand up. The long neck is covered by a short-haired mane except in the domestic horse, whose mane falls to one side. All horses have long tails, and the ass and zebra have short hair at the tip.

The large, heavy body of the rhino sits on top of short, thick legs. The eyes are small and located on each side of the head. Though their vision is not well developed, their hearing is excellent and their erect ears are rather big. Some rhinos' skin is all but naked, while other rhinos are covered with fine hair. The horns of the white rhino can grow to reach 70 inches (175 centimeters). Rhinos' horns continue to grow throughout their lifetimes, and if lost, will grow back.

Tapirs are heavy with short, fat limbs, a short tail, and medium-sized ears that grow out and up. Their eyes are small. The hind legs of the tapir are about 4 inches (10 centimeters) higher than the front legs. Due to this difference, most of the weight is supported by the longer hind legs. Tapir skin is tough and sparingly covered with hair except for the mountain tapir, whose hair is thick to protect against the cold.

Because perissodactyls eat large quantities of hard-to-chew food, their lower jaw is deep and the mouth muscles are large. The lips are thick and flexible. The stomach is simple and food passes through the digestive system quickly. This makes digestion less efficient than in other animals with more than one stomach, such as the cow. In fact, a horse digests food only 70 percent as efficiently as a cow does.


Perissodactyls are found in Asia, Africa, and America in limited populations. Tapirs are found in Central and South America and in southeastern Asia. Rhinos live throughout Central and East Africa below the Sahara Desert and in the tropical region of Asia. Horses are found in eastern and southern Africa and Asia from Near East to Mongolia. Domestic horses live throughout the world, and there are several wild populations in North America and western Australia.


Tapirs prefer to live near permanent bodies of water and enjoy tropical forests. The exception is the mountain tapir, who lives in the Andes Mountains.

Rhinos can be found in rainforests, grasslands, and scrublands (region similar to grassland but which includes scrub vegetation). These mammals must live near water for drinking and bathing. Asian rhino fossils have been found in the Himalayas at an altitude of 16,100 feet (4,900 meters), though today they're found at altitudes of up to just 6,600 feet (2,000 meters).

Horses live in grasslands and desert scrublands. Plains zebra and the mountain zebra prefer greener grasslands and savannas where vegetation is more plentiful.


Perissodactyls are herbivorous (plant-eating). The plants they eat depend on what is available in the region in which they live. Tapirs eat leaves, twigs, fallen fruit, and aquatic vegetation. Rather than eat entire plants, they consume just a few leaves from a plant and move on.

Using their upper lip to grab plants, rhinos prefer woody or grassy vegetation. They will eat fruit occasionally, but leafy greens are their favorite food. Because of their size, rhinos eat a large amount of food and drink a large amount of water almost daily. The African species, however, can live for up to five days without water if their food is moist. While black rhinos will eat bushes and trees, the white rhino prefers short grasses.

Horses eat primarily grasses, but they will also eat bark, leaves, fruits, and roots. Wild asses have adapted to their drier environment and are able to graze the desert. Horses spend 60 to 80 percent of every twenty-four hours foraging (browsing or grazing). Although most horses can go without water for three days, zebras must drink frequently. Some are able to dig waterbeds with their hooves.


Rhinos are solitary creatures seldom seen in pairs other than the mother-offspring combination. Even mated pairs don't remain together. Rhinos are territorial and have obvious displays to prove their authority, including rolling eyes, lowered head, and strutting. Males engage in brutal fights, and African rhinos inflict injury by jabbing each other with upward blows of their horns. Rhinos enjoy wallowing in mud holes because it helps keep their body temperature down and repels insects.

Female rhinos are ready to breed between the ages of three and five years. Gestation is fifteen to sixteen months in all species but the Sumatran rhino has a gestation period of seven to eight months. Mating often takes hours to complete and usually results in the birth of one calf. Rhinos weigh 55 to 145 pounds (25 to 65 kilograms) at birth and drink up to 5.5 gallons (25 liters) of their mothers' milk each day to gain 5.5 pounds (2.5 kilograms) daily. Zebras drink their mothers' milk for up to four years, though the white rhino begins eating solid food by one week of age. Males begin breeding at age ten and rhinos can live up to fifty years. What was true in the past remains true today: humans are the main predator, hunter, of rhinos.

Tapirs are also solitary mammals. They spend part of the day wallowing in mud or standing water, or simply rest in the shade. Territorial by nature, tapirs mark their territory with their urine. Most activity takes place at night. Tapirs swim with ease and water is at the center of their existence. Water provides not only food, but also safety from intruders. Able to hold their breath for minutes at a time, tapirs will seek safety from predators by immersing themselves in water. They have an acute sense of smell and hearing, but like other perissodactyls, cannot hear well. Though usually silent, they do communicate through grunts and whimpers at closer range, through whistles over greater distances.


According to HorsesAmerica.com, there are more than two hundred wild horses that are unfit for adoption and must be euthanized (YOO-thuh-nihzd), put to death, each year, so that the land can be used for the grazing of cattle. Still others are slaughtered and sold to foreign countries for human consumption. Despite this, about eight thousand mustangs (another word for "wild horses") are adopted to individuals and organizations across the country. All of this occurs under the authority of the Bureau of Land Management (BLM).

Adoption fees range from $125 to $740, and half of the horses are adopted from residents on the East Coast. Before adoption, mustangs are "re-trained" to be around humans by inmates from prisons in Colorado, New Mexico, Montana, Wyoming, Oklahoma, and California. The BLM sees this as a win-win situation. In the 90 to 150 days it takes to train a horse, the inmate develops job skills as well as a sense of trust and cooperation while the horse becomes ready for re-entry into a more domestic society.

All persons wanting to adopt a mustang must first apply and be granted approval from the BLM. Anyone with a history of physical abuse toward animals is rejected. Between two and six months after adoption, a representative from the BLM makes a surprise visit to check on the horse and determine that it is being taken care of properly.

Records show that 99 percent of (Montana) inmates who work with the mustangs and re-enter free society never commit another crime. And since 1973, more than one hundred forty thousand wild horses have been adopted.

Tapirs are sexually mature at two to four years of age. They breed year round, and females are receptive every two months. Courtship is a noisy affair. One baby is born after a gestation (pregnancy) period of 383 to 395 days. Young tapirs stay with their mothers until six to eight months of age. Tapirs have been known to live for thirty years. The primary predator of tapirs is the jaguar.

Unlike their relatives, horses are highly social. Zebras live in families of ten to fifteen individuals. These families include a territorial male, several females, and their offspring. Home ranges overlap with ranges of other families, and measure anywhere from 31 to 232 square miles (80 to 600 square kilometers). Zebras communicate via vocalization and adult males are especially noisy at night. Within groups, other males are tolerated, but only the territorial male may mate with the numerous females of the family. The black and white stripes of the zebra trigger visual neurons that attract males and females to each other. Zebras are believed to see in color, and they have binocular vision in front.

Horses are sexually mature around the age of two years, but males do not breed until around the age of five. After a gestation period of about one year, a single foal is born. The baby is able to walk on its own within an hour of birth and doesn't mind being left alone while the mother replenishes her water supply. Offspring are weaned (removed from mother's milk) at six to thirteen months. Some horses live to see forty years. Lionesses and hyenas are the main predators of horses.


Humans are largely responsible for adversely (negatively) affecting the perissodactyl populations. Tapirs and rhinos have been relentlessly hunted for food and sport, as well as for their skins, which are used to produce high quality leather goods. Rhinos are illegally hunted for their horns and other body parts, which are used in Asian medicine, supposedly to relieve headaches, heart and liver trouble, and skin disease. Horns are also used to make dagger handles. Horses are the least affected by human activity, and it wasn't until about four thousand years ago that they were first domesticated for use as transportation. Since that time, cross-breeding has become common. A mule, for example, is a cross between a male donkey and a female horse.


Nine species of Perissodactyla are listed as Endangered, facing a very high risk of extinction, or Critically Endangered, facing an extremely high risk of extinction, on the 2003 IUCN Red List. All species of rhinoceroses are included on this list. Tapir populations are declining due to deforestation leading to habitat destruction. Since 1970, the rhino population has decreased by 90 percent due to hunting. Wild horses are facing extinction due to an increase in livestock farming, which forces them from their pastures and watering holes.



Kalman, Bobbie. Endangered Rhinoceros. New York: Crabtree Publishing Company, 2004.

Murray, Julie. Zebras. Edina, MN: ABDO Publishing Co., 2002.

Penny, Malcolm. Zebras: Habitats, Lifestyles, Food Chains, Threats. Milwaukee: Raintree Publishers, 2003.

Web sites:

African Wildlife Foundation. http://www.awf.org (accessed on July 9, 2004).

"Management and Protection." Horses America. http://www.horsesamerica.com/pages/management.htm (accessed on July 9, 2004).

Myers, P. "Order Perissodactyla." Animal Diversity Web. http://animal-diversity.ummz.umich.edu/site/accounts/information/Perissodactyla.html (accessed July 9, 2004).

"Wild Horses: An American Romance, Teaching Resources Page Activities." Public Broadcasting Service (PBS). http://www.pbs.org/wildhorses/wh_teaching/wh_teaching.html (accessed on July 9, 2004).