Getting to Know Mammals

MAMMALS

Mammals are found on all continents and in all seas. It isn't easy to tell that an animal is a mammal. A combination of special features separates mammals from other animals.

Mammal milk

Only mammals can feed their young with milk produced by their body. This milk comes from special glands called mammae. A female may have two mammary glands or as many as a dozen or more. Mammal milk is very healthy for infants and immediately available.

Body temperature

Mammals are warm-blooded, meaning they keep a constant body temperature. To keep their temperature fairly constant, a mammal needs some protective covering. Hair, made of a protein called keratin, serves several functions. One function is insulation, controlling the amount of body heat that escapes into the mammal's environment through the skin.

Mammal hair

All mammals have hair at some time of their life. Some have a lot, such as gorillas, and some have very little, such as the naked mole rats. There are three types of hair: a coarse long topcoat, a fine undercoat, and special sensory hairs, or whiskers.

In some mammals, hair has unusual forms. Porcupines have stiff, sharp, and thickened hairs called quills. Anteaters have A. Cross section of a hair. B. Hairs may provide insulation and waterproofing. Specialized hair includes quills, whiskers (C), and horns (D). (Illustration by Patricia Ferrer. Reproduced by permission.) sharp-edged scales made of modified hairs. These modified, or changed, hairs are protective against predators.

Mammals that live all or most of their lives in water, such as sea otters, may have a lot of dense, long hair, or fur. Others have much less hair, but a very thick hide, or skin, plus a thick layer of fat or blubber underneath the hide.

Hair color and pattern may vary. Males and females may have different fur colors. Special color patterns, such as a skunk's black and white fur, act as warnings. Hair color can also serve as camouflage, enabling the mammal to blend into its background.

Some mammals have fur color changes in summer and winter. Colors can be entirely different. Snowshoe rabbits and weasels can be brownish in summer, and almost pure white in winter. But this only happens if there is snow where they live. If it seldom snows, weasels and snowshoe rabbits stay brown.

Top: Placental mammal development. Middle row: Marsupial mammal development. Types of uterus: A. Simplex; B. Bipartite; C. Bicornuate; D. Duplex; E. Marsupial. (Illustration by Patricia Ferrer. Reproduced by permission.)

Reproduction

Mammals have two genetic sexes, male and female. Ninety percent of mammals are placental (pluh-SENT-ul). In placental mammals, the baby develops, or grows, within the mother's body before it enters the world. What about the other 10 percent? These mammals lay eggs. There are only three egg-laying mammals alive today.:

Other mammal features

Other bodily mammal features include their ability to breathe air through their lungs. Water-dwelling mammals, such as the whale and porpoise, do this too. Mammals have jaws, usually with teeth. Mammals usually have four limbs. Mammals have a four-chambered heart. Mammals have vertebrae, or back bones, unlike invertebrates such as insects, in which there is an outside shell or structure called an exoskeleton.

This life-sized woolly mammoth model is kept in the Royal British Columbia Museum. Woolly mammoths were as tall as 10 feet (3 meters). (© Jonathan Blair/Corbis. Reproduced by permission.)

FOSSIL MAMMALS

Fossils are body parts of animals that lived very long ago. Not many long-ago mammals are preserved as fossils. But some entire mammal fossils have been discovered, such as a 10-foot (3-meter) woolly mammoth preserved in Siberian frozen ground, and an Ice Age woolly rhinoceros discovered in Poland, preserved in asphalt.

Many long-ago mammals lived in a warm, wet world. They ate soft, leafy plants. The earliest known mammals were possibly shrew-like creatures living about 190 million years ago. Later larger mammals occurred, then disappeared, or became extinct. These include the mesohippus, a three-toed horse only 24 inches (60 centimeters) high; a giant pig with a head that was 4 feet (1.22 meters) in length; and the smilodon, a huge saber-toothed cat with canine teeth that were 8 inches (20.3 The Grant's desert mole uses its powerful forelimbs to burrow through the sands of the Namib Desert in southern Africa. The golden mole moves forward (1), and enlarges the tunnel by pushing dirt up with its head and back with its claws (2). (Illustration by Jacqueline Mahannah. Reproduced by permission.) centimeters) in length. By about 15,000 years ago, long-ago people were hunting mammals with stone-pointed spears. Most of the animals they hunted are extinct for various reasons, some known, and some unknown.

WHERE MAMMALS LIVE

Underground mammals

Some small mammals spend all or most of their lives living underground. These include many species of prairie dogs, chipmunks, moles, groundhogs, Greenland collared lemmings, and Peruvian tuco-tucos. Each of these mammals has a special body design enabling it to survive underground.

Moles have large, powerful shoulders and short, very powerful forelimbs. Spade-like feet have claws, enabling quick digging. Hind feet have webbed toes, enabling the mole to kick soil backwards effectively. Velvety-type fur enables a mole to slip easily through its tunnels. And, although moles have almost no eyes, they can rely on touch, smell, and sensitivity to vibration to find underground insects and earthworms.

Sea mammals

Some mammals live in the sea, including manatees, whales, seals, and dolphins. While some need air every few minutes, a sperm whale can remain underwater for an hour and a half. How is this possible? Some sea mammals have a very low metabolism. They don't use up the their oxygen quickly and can store large amounts of oxygen in their bodies.

Tree mammals

Some mammals spend all or most of their lives in trees. Tree-dwelling mammals are often hidden from sight by leaves, vines, and branches. Tree-dwelling mammals include the Eastern pygmy possum, which nests in small tree hollows; the koala; Lumholtz's tree kangaroo, which leaps from branch to branch; the three-toed sloth; and the clouded leopard.

Flying mammals

The only truly flying mammals are bats. The sound of bat wings was first heard about 50 million years ago. Some bats are large, with a wingspan almost 7 feet (21.3 meters) wide. Some are small, as the Philippine bamboo bat, whose body is just 2 inches (5.08 centimeters) long.

Other mammals only appear to fly, such as the southern flying squirrel and the colugo, or Malayan flying lemur. These mammals have gliding membranes, skin folds from body front to legs, that, when spread out, act almost like a parachute. For example, the feathertail glider, a tiny possum, crawls along narrow branches. At branch end, it leaps out and slightly downward. Spreading its gliding membranes, it speeds through the air, landing on a nearby tree.

Mountain mammals

Some mammals spend most of their lives on mountain peaks. These include Asian corkscrew-horned markhor goats, North Mammals' hands and feet differ depending on where the animal lives and how it gets around. A. A hominid hand is used for grasping objects; B. A bat's wing is used for flight; C. A pinniped's flipper helps move it through the water. Hoofed animals move around on all fours: D. Elephant foot; E. Equid (horse family) foot; F. Odd-toed hoofed foot; G. Twotoed hoofed foot; H. Four-toed hoofed foot. (Illustration by Patricia Ferrer. Reproduced by permission.) American Rocky Mountain bighorn sheep, and Siberian ibex. Siberian ibex can stand anyplace on any pinnacle with just enough room for its four feet. North American mountain goats can climb up a mountain peak, almost going straight up. Specially shaped hooves help.

Other high mountain dwelling mammals include snow leopards and Asian pikas that can survive at 19,685 feet (6,000 meters). Gunnison's prairie dogs do well up to 11,500 feet (3,505 meters).

Desert mammals

Some mammals spend most of their lives in arid, or very dry areas. Not all deserts are sandy like Death Valley or the Sahara. Some are rocky. Other arid areas are mountainous. Desert dwelling mammals include the North African elephant shrew, white-tailed antelope squirrel, and the desert kangaroo rat. No mammal can live without water. Desert rodents have a way to extract, or get, water from their own body functions. Rodents may also get water by eating plants, seeds, roots, and insects that contain water.

Larger mammals live in arid regions too. The striped hyena can survive in stony desert as long as it is within 6 miles (9.7 kilometers) of water. Fennecs, a very small fox living near sand dunes, can go a long time without drinking. Camels can use body fluids when no water is available.

WHAT DO MAMMALS EAT?

Insect-eaters

Some mammals have mostly insect meals. Insect-eating mammals include the moles, aye-ayes and aardvarks. The aardvark Animals, such as these Rocky Mountain goats, may visit a salt lick to get some of the nutrients they need. (© Raymond Gehman/Corbis. Reproduced by permission.) has a sticky tongue that can reach out as long as 1 foot (0.3 meters) to capture its ant and termite meals.

Plant eaters

Some mammals eat nothing but plants. Plant eaters include pandas, the West Indian manatee, and the red-bellied wallaby. Some mammals have a single stomach that breaks the plant food down into small pieces. Other mammals, such as cows and camels, have a large stomach made of several parts. Each part does a separate job of breaking down difficult-to-digest plants.

Some mammals eat both plants and fruit. These include the 14-ounce (400-gram) Eurasian harvest mouse, the 100-pound (45-kilogram) South American capybara, and the African elephant. An elephant can eat up to 500 pounds (227 kilograms) of grass, plants, and fruit per day.

Meat eaters

Mammals eating mostly meat or fish are carnivorous. Carnivorous mammals have long, pointed, and very strong incisor teeth. Carnivores include polar bears, hyenas, walruses, and European Mammals have different tooth shapes for different functions. Herbivores typically have large, flattened teeth for chewing plants. Rodents' ever-growing incisors are used for gnawing. Carnivores have teeth for holding and efficiently dismembering their prey. (Illustration by Jacqueline Mahannah. Reproduced by permission.) wild cats. The European wild cat may be an ancestor of our house cats.

Omnivores

Some mammals eat just about anything. They are omnivorous. Omnivorous mammals include wolverines, raccoons, and wild pigs. Wild pigs are the ancestors of our domestic pigs.

MAMMAL SLEEPING HABITS

Day or night

Some mammals sleep during the night, others sleep during the day. The night sleepers are diurnal, active during the day. The day sleepers are nocturnal, active at night. They may have special night vision. Many desert animals are nocturnal, moving about when it is cooler.

Hibernation

Some bat species hibernate through an entire winter. Hibernation is like a very long deep sleep. When a mammal hibernates, it uses up body fat that has accumulated from food eaten in good weather. Hibernators include the North African jird, groundhogs or woodchucks, and several dormice species. Dormice enter a tree hollow or ground burrow in autumn, and don't come out until springtime.

Bears don't truly hibernate. Their sleep isn't deep. They slow down quite a bit, and nap a lot, but do not sleep through an entire winter.

A new hibernating pattern has just been discovered. Madagascar fat-tailed lemurs hibernate in tree holes when winter daytime temperatures rise above 86° Fahrenheit (30° Celsius). They sleep for seven months. Scientists belief these dwarf lemurs find less food in what is the dry season in Madagascar, so they go to into deep sleep to preserve energy until a better food supply appears.

REPRODUCTION

Mating

Some mammals mate for life, such as wolves and sometimes coyotes. More commonly, a male may mate with several females each breeding period. Or a female may mate with several males.

Some mammals have one litter each year. Others have a litter only every two or three years. But the North American meadow mouse can have seventeen litters per year. That's a group of babies about every three weeks!

There may be one or more infants in a litter. Bats, giraffes, and two-toed sloths have just one baby per year. However, the Madagascar tenrec can produce thirty-two babies in just one litter.

Opossums are marsupial animals. The mother has a pouch in which the young continue to develop after they're born. (© Mary Ann McDonald/Corbis. Reproduced by permission.)

Child care

All mammal infants need protection. They are very small compared to their parents. They may be blind and hairless. Usually females provide care. However, in a few mammal species, such as the golden lion marmoset, the male does most of the care.

Female marsupial mammals, such as opossums, koalas, and kangaroos, have a pouch, like a pocket, on the front or under the body. Their tiny babies are incompletely developed when they are born. At birth, an opossum baby is about the size of a dime. It crawls immediately into its mother's pouch and stays there until ready to survive outside. The pouch contains mammary glands so babies can feed.

SOCIAL LIFE

Solitary mammals

Some mammals are solitary. They keep company with another of the same kind only when mating or when raising young. Solitary mammals include the giant anteaters, European bison, and right whales.

Japanese macaques are social animals, and groom each other regularly. (© Herbert Kehrer/OKAPIA/Photo Researchers, Inc. Reproduced by permission.)

Group living

Many mammals live in groups. In large groups, some eat, some rest, and some keep guard. Baboons, for example, may have from twenty to 300 animals in a group. One or more adult males lead each group. If a predator, such as a leopard, approaches, the males take action against it, while the females and young escape.

Some mammals travel in herds. Musk oxen travel in closely packed herds of fifteen to 100 individuals. These herds include males and females. Bighorn sheep females travel in herds of five to fifteen, with a dominant ewe, or female, as the leader.

Pack mammals get their food by cooperation. They work together to bring down much larger prey. Dingoes, killer whales, and lions hunt in packs.

MAMMALS AND PEOPLE

Domesticated mammals

About 14,000 years ago, humans began controlling, or domesticating, certain animals. This made humans' lives easier. Horses have been domesticated for practical uses, such as transportation, and for entertainment, such as horse riding and racing. (© Kevin R. Morris/Corbis. Reproduced by permission.) Rats can spread diseases that affect livestock and people. In addition, they eat and contaminate feed and their gnawing destroys buildings. (Jane Burton/Bruce Coleman, Inc. Reproduced by permission.) The earliest domesticated mammal was probably the dog. Some scientists think hunters adopted wolf cubs and trained them to smell out game, animals they hunted for food.

People use mammals for many purposes. Cows provide meat, milk, cheese, butter, and hide. Camels, yaks, and Indian elephants carry or pull heavy items. Water buffaloes do hauling and can provide milk. Horses provide transportation and racing activities. Other domesticated animals include rabbits, pigs, goats, sheep, cavies, and capybaras.

People keep animals as pets. Common mammal pets are dogs, cats, guinea pigs, and hamsters.

Pest mammals

Some mammals are considered pests. These include rats, mice, and, depending where they live, gophers, rabbits, and ground squirrels. Rats can transmit disease-carrying fleas. Rabbits and gophers eat garden and food plants.

ENDANGERED MAMMALS

Mammals in danger

Of about 5,000 mammal species currently existing, over 1,000 are seriously endangered. Few wild mammals can live outside their natural habitat. When land is cleared for farming or housing, animals making homes there must leave, if there is any place for them to go. If not, they die from starvation or (because they are easily seen) from predators. Slowly, or quickly, the mammal species disappears.

Many human habits lead to endangerment. Hunting for amusement, killing for fur or body parts, native and commercial killing for food, fishing gear entrapment, land-destructive wars, and the illegal pet trade all take their toll. So do chemicals.

Some mammals are probably on the way to extinction, or total elimination. There are only about sixty Java rhinoceros left in the world. The Seychelles sheath-tailed bat has only about fifty individuals remaining. Yellow-tailed woolly monkeys number no more than 250 individuals. Mediterranean monk seals may be killed by scuba divers, and number only 600 individuals.

Saving endangered animals

Today many people are trying to save endangered animals. Methods include zoo breeding, establishing forest reserves, and training native populations that animals can be an economic benefit. Ecotourism, people visiting a country to see its animals in their natural habitat, is increasing. There are laws against importing and exporting endangered species. And, in some parts of the world, there are laws against land destruction.

Some mammals have possibly been rescued from immediate extinction. The American bison once roamed the North American prairies, numbering about 50 million. After slaughter by soldiers and settlers for food and sport, by 1889 only 541 remained alive. Now, in the United States, there are about 35,000 in protected areas. California northern elephant seals were once reduced to fewer than 100 members due to hunting. Today, protected, there are about 50,000. The ibex was once hunted for supposedly curative body parts and few were left. But in 1922, a National Park was established in the Italian Alps, where several thousand now live. The Mongolian wild horse, once thought to be extinct, now has a special reserve in Mongolia.

Too late to save

Some mammals became extinct only recently. Recently extinct animals include Steller's sea cows, which became extinct in about 1768. The Tasmanian wolf was last seen in 1933, eliminated by bounty hunters. The African bluebuck disappeared from Earth in 1880. The quagga, from southern Asia, was hunted for hides and meat. The last known quagga, a relative of the zebra, died in a Dutch zoo in 1883.