Perissodactyla

(Odd-toed ungulates)

Class Mammalia

Order Perissodactyla

Number of families 3

Number of genera, species 6 genera; 16 species

Introduction

Perissodactyla are exclusively large terrestrial herbivores. Also commonly known as perrisodactyls, or odd-toed ungulates, this order is extremely diverse; from the robust, horned white rhinoceros (Ceratotherium simum) to the sleek, slender, and striped mountain zebra (Equus zebra).

Traditionally, there are three families within the order Perissodactyla: the Tapiridae (tapirs), the Rhinocerotidae (rhinoceroses), and Equidae (asses, horses, and zebras). These three families include six genera and 16 species.

Evolution and systematics

Despite excellent fossil records, the phylogeny of Perissodactyla is not well understood in terms of both the relationship within the order and the position among other orders of mammal. The perissodactyls as well as artiodactyls originated from the Condylarthra, the dominant mammalian herbivores of the early Paleocene (about 65 million years ago [mya]). Condylarths are considered to be ancestors of many of the other lineages of large mammals. Despite the superficial similarities between horses and cows, rhinos and hippos, tapirs and pigs, the former of each pair belongs to the Perissodactyla,

and the later to the Artiodactyla. The similarities between them have largely come about due to convergent evolution. However, mitochondrial genomes studies suggest that the order Perissodactyla is part of one eutherian clade, comprising also Pholidota, Carnivora, and Cetertiodactyla (Artiodactyla and Cetacea). The oldest identifiable perissodactyl fossils are from the early Eocene (about 50 mya). By this time, 14 radiated families were evident. During this epoch, perissodactyls were dominant ungulates, far outnumbering the artiodactyls. By the end of Oligocene (25 mya), eight families were extinct. By the early Miocene epoch, only the tapirids, rhinocerotids, equids, and Chalicotheriidae remained. This last family included unusual ungulates with large forelimbs and short hind limbs adapted for standing semi-erect to feed on tall trees. As the perissodactyls declined, there also seems to have been some definite ecological replacement of them by artiodactyls.

Originating in the early Eocene epoch of North America, tapirs migrated into Asia and Central and South America. Tapirs were extirpated throughout most of North America by the late Pleistocene epoch. A combination of migration and extirpation resulted in a discontinuous distribution today. The current genus Tapirus dates from 20 mya in the Miocene epoch. There are four extant species in the single genus Tapirus. Tapirs belong to among the most primitive large mammals in the world.

Fossil evidence of rhinocerotids dates from the late Eocene in Asia and North America. Most of today's genera date from the Miocene (10–25 mya). They were extinct in North America by the end of the Pliocene (2 mya). Rhinocerotids were abundant and widespread in the Old World until the late Pleistocene epoch (about 60,000 years ago). The largest land mammal that ever lived was a rhinocerotid, Indricotherium transouralicum (Baluchitherium grangeri), which was at least 16.5 ft (5 m) high at the shoulder and to 44,000 lb (20,000 kg) of body mass. Mitochondrial analysis identified a basal divergence between the African and the Asian species about 26 mya. There are four extant genera (Diceros, Rhinoceros, Dicerorhinus, and Ceratotherium), with five living species.

The fossil history of equids is one of the best documented for any mammalian family. This history shows increasing body size or skull proportion and reduction of the number of digits. However, the evolution of equids was not a directed progressive process, but a complex radiation of numerous divergent and overlapping lineages. Equids passed most of their evolution in North America, with migration to Eurasia and Africa during the Miocene and to Central and South America in the Pliocene and Pleistocene epochs. The earliest of the horse-like ancestors, Hyracotherium, appeared in the Eocene, about 54 mya. It was a small dog-size mammal that browsed on low shrubs of forest floor. When grasses extended in the Miocene, equids began to radiate. Overall body size increased, which reduced relative nutritional demands. By the early Pleistocene (2 mya), the one-toed equids had spawned the genus Equus, which rapidly spread. As environment changed, populations became isolated, giving rise to the living species. The first to split off from the equid stream was the Grevy's zebra (Equus grevyi), which, despite its stripes, is only distantly related to the other two zebra species. However, the ancestor of all equines was probably striped. The horses became extinct only about 10,000 years ago in the New World, but horses were reintroduced by the Spanish conquistador Hernando Cortes in 1519. The number of extant equid species is open to debate: seven to 10 species, all in the genus Equus, are recognized. Many subspecies and regional forms (mainly in zebras) are known.

Physical characteristics

The unifying characteristic of Perissodactyla is their single toe (or three toes together) bearing the weight of the animal, with the axis of each limb passing through the enlarged third digit. Tapirs have four digits on the forefeet and three digits on the hind feet, whereas rhinos have three digits on all feet. The single third digit is the only one remaining in equids. This is a condition of maximum specialization for running. The functional toes in both Perissodactyla and Artiodactyla end in hoofs, but the structure of the foot is different. The median metacarpals and metatarsal bones are not fused into a cannon bone as in artiodactyls. Perissodactyls have a deep pulley-like groove in the proximal surface of the anklebone (astralagus), which limits the limbs to forward-backward movements. The fibula does not articulate with the heel bone (calcaneum).

The perissodactyls show great range in body size and shape. The smallest species is the mountain tapir (Tapirus pinchaque), which weighs to 485 lb (220 kg). The largest species, the white rhinoceros (Ceratotherium simum), can weigh over 7,700 lb (3,500 kg). In most species, adult males are notably larger than females, while in some tapirs, the females are bigger.

The general form of tapirs is heavy, with short and stout limbs, a short tail, medium-sized oval ears extending out and upwards, small eyes flush with the head, and short fleshy proboscis formed by the upper lip and nose, with the nostrils located at the tip. The back of tapirs is arched, with the hind legs about 4 in (10 cm) higher than the forelegs, so the hind feet support the majority of their weight. This may be related to the fourth toe being absent on the hind feet. The compact, streamlined shape of the body is ideal for pushing through the dense undergrowth of the forest floor. Neotropical tapirs have short bristly manes extending along the back of the neck, protecting the most vulnerable part of the body against predators. Tapir skin is tough and covered with sparse hairs; only the mountain tapir has a thick coat, which protects it from the cold.

Rhinoceroses are large, heavy animals with short, stout legs. The eyes are small and pig-like, located on the sides of head. Vision is not especially acute. The ears are erect, tubular, tufted with hair, and fairly large, and hearing is excellent. The skin is thinly covered with hairs in Dicerorhinus and is nearly naked in the other species; in Rhinoceros, the skin is deeply folded across the back. One horn in Rhinoceros or two horns in all other rhinos have no bony core or keratinized sheath, but a dermal mass of agglutinated hair rest. The horns are developed upon a rough vascular cushion of bone on the midline of the nasal bones for the anterior horn and on the midline of the frontal bones for the posterior horn, when present. The horns can reach 70 in (175 cm) in length in the white rhinoceros (Ceratotherium simum). Rhinoceros horns grow throughout the animal's life, and are re-grown if lost. A further peculiarity of rhinos is that, as in elephants, the testes do not descend into a scrotum. The penis, when retracted, points backwards so that the urine is directed to the rear by both sexes.

All equids are medium sized with long heads and necks and slender legs. The ears are moderately long and erect, but can be moved to localize sounds. An erect mane covers the neck, but in the domestic horse, it falls to the side. All equids have long tails, with flowing hair in horses or with short hair only at the tip in ass and zebras. All African equids are partially striped on the legs (ass) or wholly black and white striped (zebra). The coat of Asian asses and horses are more uniform in color: dun in Przewalski's horse (Equus caballus przewalskii), from tan to gray in asses.

The skull in all species is elongated by the lengthening of the rostrum. The cheek teeth of all perissodactyls are brachydont (low-crowned), hypsodont (high-crowned), or lophodont (with elongated ridges), with 24–44 teeth. Three upper incisors are retained in the tapirids and equids; in the rhinos, they are reduced in numbers, or absent altogether. In tapirs, the canines are sharp, conical, and relatively short, separated by a diastema (space) from the cheek teeth. Perissodactyls have to consume large quantities of tough fibrous food, so the lower jaw is very deep and the masseter muscle is very large. The lips are thick and freely movable in all species.

In the Perissodactyla, the stomach is simple, and the cecum is enlarged to form a chamber in which microorganisms live and digest plant cellulose (hindgut fermentation). Food passes through the digestive system about twice as fast as through that of ruminating artiodactyls. Because food is retained for less time, digestion is less efficient. For example, the digestive efficiency of a horse is only about 70% of that of a cow. Perissodactyls compensate for reduced efficiency by consuming more food per unit of body weight. The enlarged cecum and colon provide storage and surface area for absorbtion of nutrients. In white rhinoceros (Ceratotherium simum), the cecum consists of a small chamber, whereas the colon is enlarged. The cecum may be functionally replaced by the well-developed colon, which may act as the main fermentation tank. Perissodactyls have a bicornuate uterus, diffuse placentation, and no clavicle or penis bone (baculum). The gallbladder is missing, and milk nipples are placed in groins.

Distribution

Perissodactyla have limited distribution in Africa, Asia, and America, but some hundred years ago they occupied much bigger areas of these continents, as well as Europe. The tapirs have a discontinuous distribution in the Neotropical Central and South America and in southeastern Asia. The rhinoceroses are distributed in sub-Saharan Central and East Africa and in the Indomalayan region of tropical Asia. The natural distribution of equids includes eastern and southern Africa and Asia from Near East to Mongolia. The wild horses became extinct in Europe during the nineteenth century. Only the domestic horse is found worldwide, and it has spawned feral populations in North America on the western plains and on east coast barrier islands, and in the mountains of Western Australia.

Habitat

Perissodactyls are able to occupy different habitats from the deserts to tropical rainforests. Tapirs usually do not occur far from permanent water and are associated with a variety of moist tropical forested habitat, including dry deciduous

forest as well as multistratal tropical evergreen forests. Only one species, mountain tapir, is adapted to higher elevations to 14,700 ft (4,500 m) in the Andes and predominantly inhabit the paramos and dwarf forest. The other species occur in lowland and premontane forests, or in swampy grasslands. The lowland tapir (T. terrestris) is also common in dry parts of Paraguayan and Argentine Chaco.

Depending on the species, rhinoceroses occupy tropical rainforests, floodplains, grasslands, and scrublands. All species are dependent on a permanent water supply for frequent drinking and bathing. African rhinoceroses occupy drier savannas and arid scrublands as well as mountain rainforest. They mostly prefer edges of thickets and savannas with areas of short woody regrowth and numerous shrubs and herbs. Asian rhinos inhabit both the swamps and dense rainforests to the elevation 6,600 ft (2,000 m). Fossil forms has been found as high as 16,100 ft (4,900 m) in the Himalayas.

Equids inhabit short grasslands and desert scrublands. Only the plains zebra (Equus burchellii) and the mountain zebra (Equus zebra) occupy lusher grasslands and savannas where the vegetation is more abundant. The remaining species live in the more arid environments with sparsely distributed vegetation.

Behavior

Some perissodactyls are highly social mammals, but others live more or less solitary. Tapirs tend to move singly except for female and her dependent young. They often spend part of the day resting in mud wallows or standing water or lying in shaded thickets. Tapirs frequently use the same trail to and from wallowing and feeding sites. They mark their territories and daily routes with urine. Tapirs defecate in water or at special places near water. Communal use of trails and defecation sites permits a loose communication system within a population. Tapirs are mostly nocturnal and only partly diurnal animals. They confine much of their activity to the darkness. In the Central American tapir (Tapirus bairdii) in Costa Rica, diurnal movements could encompass as little as 7.5 acres (3 ha) or as much as 67 acres (27 ha). Nocturnal movements are larger, with activity included to 445 acres (180 ha). An adult and subadult of mountain tapir in central Colombia moved within the range of about 4.3 mi² (11 km²). Tapirs are excellent swimmers and their existence is centered close to water, which offers lush feeding grounds and escape routes from predators. Tapirs can cross deep streams by walking on the bottom. They may seek refuge in water and can stay submerged for several minutes. Tapirs have an acute sense of smell and good hearing, but seem to have poor eyesight. Tapirs walk with the proboscis close to the ground, so they can detect the scent of predators. When threatened, they usually crash off into thick brush or into the water or defend themselves by biting. Tapirs are usually silent, but communicate over distance with long whistling calls. Grunts, hiccups, and whimpers are used at close range. A low snort may be given in alarm. Density of tapirs can reached 2.1 animals per mi² (0.8 animals per km²). Males may fight ferociously to gain mating rights with sexually receptive females. Remarkable associations between tapir and a male coati exist. Tapirs can become infested with ticks and coati fed on the blood-engorged ticks by gleaning them from the tapirs' bodies.

Aside from mother and offspring pairs, rhinos generally are solitary. Small group of immature individuals may form in Indian (Rhinoceros unicornis) and white rhinos. Several individuals may come together mainly in favored wallowing areas or saltlicks. Mated pairs may form couples for a short time. The tolerance of dominant individuals, particularly males, varies by species, by region, and in response to changes in density. Rhinos display territorial behavior. Displays between males are very conspicuous: there is much strutting, broadsides with lowered head, flattened ears, and rolling eyes. Various snorts during encounters seem to have different shades of meaning. Home ranges of males can cover 50 mi² (130 km²), but some are as small as 0.4 mi² (1 km²). Females and their immediate offspring occupy home ranges 1.5–6 mi²(4–15 km²), overlapping with one or more female neighbors. When territories are maintained by resident males, their border patrolling and scent marking leave foot-scuffs, dung middens, urine spray, rubbing posts, and horned vegetation along boundaries. Males of all species sometimes fight viciously, inflicting gaping wounds. Both African species fight by jabbing one another with upward blows of their front horns. In contrast, the Asian rhinos attack by jabbing open-mouthed with lower incisor tusks, or in the case of Sumatran rhinoceros (Dicerorhinus sumatrensis), with the lower canines. Black rhinoceroses (Diceros bicornis) have a reputation for unprovoked aggression, but very often their charges are merely blind rushes designed to get rid of the intruder. Some rhinos may travel 9.5–12.5 mi (15–20 km) within 24 hours, and some individuals of the Sumatran rhinoceroses have been observed swimming in the ocean. Temperature control, digestion, and scent communication all depend upon water, and rhinos are unable to survive extreme droughts. The wallowing of rhinoceros is probably necessary to help control body temperature and to reduce insect harassment. The sense of smell is

well developed. Rhinos have poor vision and are unable to detect a motionless person at a distance of more than 35 yd (30 m). Social systems can be related to differences in the density and distribution of food resources. Rhinos rarely exceed local densities of 0.4–2 animals per mi² (1–5 per km²).

Equids are highly social mammals that exhibit two basic patterns of social organization. Zebras are high-density, tropical grassland horses; asses are low-density, desert-adapted forms. The basic social units of zebras is the family group (or harems), generally 10–15 individuals made up of a highly territorial male, several females, and their offspring. Nonbreeding males, and occasionally young females, form small unstable bachelor groups. Each harem has a home range, which overlaps with those of neighbors. Home ranges vary, depending on the quality of the habitat, from 31–232 mi²(80–600 km²). In the plains zebra, temporary aggregations of 100,000 individuals may form, depending on ecological conditions. Zebras very often associate with other ungulates. Social contacts are primarily by sounds, and zebras are extremely vocal. The adult males are particularly noisy during nocturnal movements. For each social unit, the stallion's individual song (a glottal-barking bray) becomes the focal point for all harem members. The second social system, typified by the asses and Grevy's zebra, involves more ephemeral adult associations, rarely lasting longer than a few months. Temporary aggregations of one or both sexes are common, but most adult males live alone within territories from 0.8–8 mi² (2–20 km²). Within this territory, owners obtain exclusive mating access to receptive females that wander through them. Other males are tolerated within the territory, but the territory holder monopolizes all access to females. The preferred range of females with offspring is often within vast territories held by mature males. Dung piles mark boundaries of territories. Estrus stimulates frequent loud braying in males. Dominance is asserted by a proud posture, with arched neck and high-stepping gait. Submission is signaled by a lower head and raised tail. The stripes of zebra appear to serve as a visual bonding device. Black and white stripes stimulate visual neurones very strongly and appear to make them attractive to each other. The widespread theory that their strips are camouflage is therefore contradicted by the zebra behavior. The aggressively antisocial behavior of territorial animals would thus appear to be counteracted to some extent by visual attractiveness. Notwithstanding this, both males and females are mutually antagonistic and even young foals prefer members of the opposite sex. Equids are most active when the weather is cooler: at dusk, dawn, and during the night. Equid eyes are set far back in the head, giving a wide field of view. Their only blind spot lies directly behind the head, and they even have binocular vision in front. They probably can see color and, although their daylight vision is most acute, their night vision ranks with that of dogs or owls. Moods are often indicated visually by changes in ear, mouth, and tail position. Males use the flehmen, or lip-curl, response to assess the sexual states of females, and the womeronasal, or Jacobson organ, which is used for this is well developed. Reproductive competition among males for receptive females is keen. This begins with pushing contests, or ritualized bouts of defecting and sniffing, biting at necks, tearing at knees, or thrusting hind legs towards faces and chests. In contrast, amicable activities such as mutual grooming cement relationships among the females. All equids keep their coat in condition by dust bathing, rolling, rubbing, and some mutual nibbling.

Feeding ecology and diet

All perissodactyls are strictly terrestrial herbivores. The tapirs are browsers and frugivores and selectively feed on

leaves, twigs, various fallen fruit, grass, aquatic vegetation, and occasionally on cultivated crops, but prefer green shoots. They follow a zigzag course in feeding, moving continuously and taking only a few leaves from any one plant. Although they may crush many seeds of fleshy fruit, the tapirs are an important disperser of seeds, since some pass through its gut unharmed. In Mexico and South America, tapirs sometimes damage young maize and other grain crops, and in Malaya, they are reputed to raid young rubber plantation.

Rhinos forage on woody or grassy vegetation and occasionally fruits, but prefer leafy material when available. They need a large daily intake of food to support their great bulk. The main rhino specialty is an ability to feed on coarse plant material. Because of large size and hindgut fermentation, rhinos can tolerate relatively high contents of fiber in their diet. Rhinos are more selective than elephants, but less so that most antelopes. In black rhinoceroses, there are special seasonal preferences for legumes, while certain other plants are always avoided. Salt is a major attraction. All rhinos are basically dependent upon water, drinking almost daily. But under arid conditions, both African species can survive up to five days

without water, if their food is moist. In white rhinoceroses, a preference for short grass areas and seasonal movements to avoid waterlogged long grass confirm that this species evolved within a larger ungulate community that maintained short swards. In areas of high density, the rhinos themselves maintain grazing lawns. Linear pathways may form between grazing and water points. Frequent alterations between grazing and resting changes to long midday rest at the height of the dry season. Asian rhinos are browsers and during the course of feeding, branches up to 1 in (2 cm) thick are torn off, stems are broken or decorticated, and trees up to 6 in (15 cm) in diameter are uprooted when they lean against the tree. The rhino thus modifies the environment to meet dietary needs.

All equids forage primarily on fibrous foods. Although horses and zebras feed mainly on grasses and sedges, they will consume bark, leaves, buds, fruits, and roots, which are common for asses. Wild asses are well adapted to graze the harshest desert grasses. They used their incisors and hooves to break open tussocks. Equids can sustain themselves in more marginal habitats and on diets of lower quality than can ruminants. Equids spend most of a day and night foraging (about 60–80% of 24 hours activity). Equids are able to go without water for about three days, but zebras are totally dependent on frequent drinking. Some local populations can dig waterbeds with the hooves. Mountain zebra often occupy separate summer and winter ranges in distances up to 75 mi (120 km) apart. They move between pastures and water sources on well-worn traditional paths. The timing and intensity of grazing is strongly influenced by temperature and season, with animals taking shelter and becoming inactive during the middle of the day in summer.

Reproductive biology

Perissodactyls are long-lived, very slow breeders with low recruitment rate. Sexual maturity in tapirs is reached at two to four years of age. Breeding occurs at any time during the year and females can be sexually receptive every two months. Mating is preceded by a noisy courtship. Male and female stand head to tail, sniffing their partner's sexual parts and moving around in a circle at an increasing speed. They nip each other's feet, ears, and flanks, and prod their bellies. Usually, a single precocial young (twins are rare) is born after a gestation of 383–395 days. The average neonatal weight is about 5 lb (2.3 kg). Young have a reddish brown coat with camouflage of white spots and lines. For the first week after birth, it remains in a secluded spot while the mother feeds, and she returns periodically to nurse. The calves actively follow the mother at 10 days of age and stay with her for six to eight months, by which time the juvenile pelage is replaced with adult pelage and it is nearly adult size. A female in her prime probably produces a calf every second year. Some animals are known to live for 30 years.

Rhino females become sexually mature at three to five years of age and bear their first calves when six to eight years of age. Females are probably polyestrous, coming into heat every 46–48 days. In the African rhinos, a birth peak occurs from the end of the rainy season through the middle of the dry season. Gestation is 7–8 months in the Sumatran rhinoceros,

and 15–16 months in the other species. Mating in rhinos can be a prolonged business with several hours' fore-play, and copulation often lasting for one hour. Births, usually a single non-horned calf, occur at intervals of two to five years. The body weight of newborn calves varies 55–145 lb (25–65 kg), according the species, and is about 4% of the mother's weight. Mothers produce to 5.5 gal (25 l) of milk a day and the calves gain 5.5 lb (2.5 kg) a day. Young nurse for one to four years, although the white rhinoceros begins to eat solid food by one week of age. Calves suckle milk for up one or two years and only begin to drink water after four or five months. Males first become sexually potent at seven to eight years of age, but generally do not breed before 10 years old. Nonetheless, rhinos formerly suffered low levels of natural mortality, a trait that goes with long life up to 50 years. In spite of a long lifespan, this is one of slowest recruitment rates of any large mammal.

Both young male and female equids become sexually mature at about two years age. Males do not breed until they leave the family group and gain access to other females, which is at five years of age. A single foal is born after a gestation period about a year. Only in the Grevy's zebra does gestation last slightly longer (about 400 days). Births and subsequent mating 7–10 days later occur during the wet season, when vegetation is more abundant. Neonates are precocial. Young are up and about within an hour of birth. Initially, the foal is passive and fearless and will remain alone for long periods while the mother seeks water to maintain her lactation. The offspring begin to graze at one month of age and are weaned at 6–13 months of age. Some animals are known to live for 40 years.

Conservation

There are only 16 extant species of Perissodactyla. Of these, 13 (more than 81%) are threatened with extinction and listed as endangered species (IUCN Red Data Books, CITES). A few species like the quagga (Equus quagga) have become extinct (the last animal died at the Amsterdam Zoo in 1883), but many other subspecies, forms, or populations also disappeared. The principal threats to perrisodactyls are the degradation of their natural habitat and human activities, mainly poaching as well as legal over-hunting. Local wars also contribute to the decline of the animals in various areas. The Special Survival Commission of IUCN—The World Conservation Union is interested in the perrisodactyls and has Specialist groups for equids, Asian rhinos, tapirs, and Afrotherian conservation.

Although tapirs have survived for millions of years, their future is not secure. All species of tapirs suffer from loss of

habitat due to huge deforestation for agriculture. Most populations are declining in number and distribution. The Malayan tapir (Tapirus indicus) and mountain tapir are considered Endangered or threatened. Tapir meat is much prized, and tapirs are easy to locate with dogs or calls and thus vulnerable to local extinction. Tapirs avoid people and leave areas of human activities, even when hunting is controlled. The best management for survival of tapirs is forest reserves like Taman Negara in Malaya.

Populations of all rhinoceroses have declined during the last 150 years and drastic declines will probably continue. By 1970, some 70,000 black rhinoceroses were estimated to have survived in Africa. This was a fraction of the number of existing rhinos at the turn of the century. By 1990, the total number of this species living within 38 officially protected conservation areas was about 3,300. Today, the estimate is about 2,700 individuals. All species are considered to be Endangered, with the Asian species near extinction. The population of Javan rhinoceros (Rhinoceros sondiacus) is now confined to a remnant of 60 animals in the Ujung Kulon Reserve in western Java and in National Park Cat Tien in Vietnam. The Sumatran rhinoceros is now restricted to perhaps 150 animals, and the Indian rhinoceros to a few reserves in Assam, west Bengal, and Nepal, with a total number of about 1,500 animals. Rhinos are among the world's most endangered mammals. The natural habitat destruction due to the enormous increase of human population, as well as the destruction of forest by elephants, plays a significant part in the threats to the survival of these animals. Rhinos have been brought to extinction because of the very large amounts of money that people are prepared to pay for rhinoceros products. The best protection the animals have is to remain in well-managed national parks and game reserves. White rhinoceroses have been successfully translocated to parts of their former range in southern Africa and its abundance has increased from about 20 animals to 13,000. Meanwhile, strict international legislation is intended to prevent trade with rhinoceros products and to punish those profiteers who deal in them. In many of the countries where rhinoceroses live, heavily armed patrols of game wardens battle with equally determined bands of poachers. Until cultural and environmental attitudes have changed, survival of rhinos will continue to depend upon captive or closely managed populations.

Despite the proliferation of domestic horses, their wild relatives are in a precarious situation. Several species are Endangered. These include Przewalski's horse and African ass (E. africanus), both of which are probably Extinct in the Wild. Their only immediate salvation lies in captive breeding and release back to available habitats in the wild. Many Przewalski's horse individuals were produced at Prague and Hellabrun zoos, and many African asses at Basel Zoo and Hai Bar Reserve in the Negev Desert. The release of Przewalski's horse to China in 1988 (from Hellabrun) and to the Mongolian desert (from Prague) is a very good example of species protection. In Europe, the last tarpans (E. caballus) died in 1806 in Poland and in 1879 in Ukraine. Almost all subspecies of Asiatic asses are seriously threatened: the Persian onager (E. hemionus onager), sometimes considered a distinct species, is Endangered; the kulan (E. h. kulan) occurs only in a reserve on the Barsakelmes Island in the Aral Sea; the khur (E. h. khur) occurs only in the Danghandra Reserve in India; and the Syrian onager (E. h. hemippus) is now Extinct. The true plains zebra (E. burchelli burchelli) is also Extinct since 1910. Populations of both subspecies of the mountain zebra, the Cape mountain zebra (E. zebra zebra) and Hartmann's mountain zebra (E. z. hartmanni), are small and are protected in national parks or reserves, but those of Grevy's zebra have been drastically reduced, as their beautiful coats fetch high prices. However, the primary threat to all equids has come from increased livestock farming, leading to their exclusion from traditional pastures and watering places. It would be tragic if these wonderful creatures were to go the way of the quagga.

Significance to humans

The important position of the perissodactyls in most communities of large herbivores, their use of habitat, size, social organization, and ecology, even their horns, have all exposed them to damaging interactions with humans; yet, those same characteristics have been the salvation of some. Humans are partly responsible for the dwindling numbers of perissodactyls since the Pleistocene. From the glacial and interglacial epochs in Eurasia comes a wealth of evidence from societies culturally dependent upon the hunting of perissodactyls and other ungulates. Cave paintings, drawings, and carvings made by ancient people in many areas of world bear witness to the relationship that has existed between man and perissodactyls since the dawn of human history. The crucial event in this relationship was the domestication of some equids. Despite the strong protection of most of extant wild species of perissodactyls, some of them still have a great importance for some local native nations as a food. Limited species are legally hunted for meat or for trophy.

Tapirs are hunted for food, sport, and for their thick skins, which provide good quality leather, much prized for whips

and bridles. The lowland tapir is quite easy to tame, and early colonists used them for field work.

Rhinos are illegally harvested for their horns, which, with other body parts (hide, hoof, teeth, various organs, blood, urine), are valued in traditional Asian medicine for supposed aphrodisiac and medicinal properties. While ground rhino horn is used as an aphrodisiac in parts of north India, its main use in China and neighboring counties of the Far East is as a fever-reducing agent. It is also used for headaches, heart and liver troubles, and for skin diseases. Rhino horns have also been used traditionally for making handles of daggers (jambia) worn by men in the Middle East as a sign of status. Between 1969 and 1977, horns representing the deaths of nearly 8,000 rhinos were imported into north Yemen alone. Until recent time, the hide and horn of both African species were fashioned into shields for use in battle or tribal ceremonies. As the number of rhinoceroses declines, the market value of their products naturally increases, so that today, horns are often hoarded as a good investment for the future. Under such circumstances, it is hardly surprising that rhinoceros are hunted wherever they live.

Horses and donkeys were the last of common big animals to be domesticated, and they have been the least affected by human activity. The first domestic horses appeared during the late Neolithic at about 6,000 years ago, when they may have initially been used for food. Surprisingly late, about 4,000 years ago, the use of the horse as a means of transport occurred. This event caused a revolution in the human mobility race and the development of modern techniques of warfare. All species of equids can interbreed, including the zebras, and hybrids can produce more or less viable offspring. Different species do not normally interbreed in nature and it usually requires human guile and expertise to bring it about. Hybridization between horses and donkeys occurs relatively often. The production of mules (offspring of a male donkey with a female horse) is easier than the production of hinnies (offspring of female donkey and a male horse). Today, the practical importance of domestic equids is much higher for humans than in extant wild species.

Many localities where tapirs, rhinoceroses, and wild equids occur now attract humans to observe these marvelous mammals in their mystery and beauty.

Resources

Books

Corbet, G. B., and J. E. Hill. The Mammals of the Indomalayan Region: A Systematic Review. New York and Oxford: Oxford University Press, 1992.

Eisenberg, J. F., and K. H. Redford, eds. Mammals of the Neotropics. The Central Neotropic. Volume 3. Ecuador, Peru, Bolivia, Brazil. Chicago and London: The University of Chicago Press, 1999.

Estes, R. D., and D. Otte. The Behavior Guide to African Mammals. Berkeley: University of California Press, 1990.

Feldhamer A., L. C. Drickamer, S. H. Vessey, and J. F. Merritt. Mammalogy: Adaptation, Diversity, and Ecology. New York: McGraw-Hill, 1999.

Kingdon, J. The Kingdon Field Guide to African Mammals. London: Academic Press, 1997.

Reid, F. A. A Field Guide to Mammals of Central America & Southeast Mexico. New York and Oxford: Oxford University Press, 1997.

Wilson, D. E., and D. M. Reeder. Mammal Species of the World. Washington, DC: Smithsonian Institution Press, 1992.

Periodicals

Arnason, U., and A. Janke. "Mitogenomic Analyses of Eutherian Relationship." Cytogenetic Genome Research 96(2002): 20–32.

Eisenmann, V. "Browsers and Grazers: Symphyseal Shapes in Equids and Tapirs (Perissodactyla, Mammalia)." Geobios, Lyon 31 (1998): 113–123.

Froehlich, D. "Quo Vadis Eohippus? The Systematic and Taxonomy of the Early Eocene Equids (Perrisodactyla)." Zoological Journal of the Linnean Society, London 134 (2002): 141–256.

Norman, J. V., and M. V. Ashley. "Phylogenetics of Perissodactyla and Tests of the Molecular Clock." Journal of Molecular Evolution 50 (2000): 11–21

Robinson-Rechavi, M., and Graur D. "Usage Optimalization of Unevenly Sampled Data through the Combination of Quartet Trees: A Eutherian Draft Phylogeny Based on 640 Nuclear and Mitochondrial Proteins." Israel Journal of Zoology 47 (2002): 259–270.

Organizations

The World Conservation Union (IUCN)/Species Survival Commission. Rue Mauverney 28, Gland, 1196 Switzerland. Phone: 41 (22) 999-0152. Fax: 41 (22) 999-0015. E-mail: ssc@iucn.org Web site: <http://www.iucn.org>

Jaroslav Cerveny, PhD