What is the same about a bat, a cat, a kangaroo, a shrew, and you? You and all these animals are mammals.

Most mammals are covered with hair or fur. Most mammals are animals that give birth to live young instead of laying eggs. All mammal mothers care for their babies and feed them mother’s milk. Mammal babies learn by watching their parents. Mammals are generally smarter than other kinds of animals.

MANY MAMMALS

There are about 4,600 species (kinds) of mammals. Most mammals live on land and move about on four legs. There are also mammals that walk or hop on two legs, mammals that live in water, and mammals that can fly.

The world's largest mammal is the blue whale. The blue whale lives in the ocean and can be more than 80 feet (24 meters) long. The smallest mammal is the Kitti's hog-nosed bat. Scientists discovered this tiny bat in 1973 in the forests of Thailand. It is about the size of a bumblebee.

Some mammals live a long time. Horses can live about 20 years. Chimpanzees can live about 50 years, and elephants can live about 60 years. Humans live longer than any other mammal. A few humans have lived to be more than 110 years old.

Shrews are mouselike mammals that live very short lives. Most shrews live less than one year.

WHERE DO MAMMALS LIVE?

Mammals can live in all kinds of places. They can live in hot places, cold places, and places in between. Mammals are warm-blooded. They keep their bodies at about the same temperature wherever they are. Mammals use food energy to keep their bodies warm when it is cold outside. Mammals sweat to get rid of body heat when it is hot outside.

Mammals  adapted (changed) over a long time to live in very different places. Polar bears, for example, have thick fur and a layer of fat that keeps them warm. These features let them live in freezing cold near the North Pole. Their fur is white to blend in with the ice and snow.

Camels are mammals adapted to live in hot, dry deserts. Camels can go for a long time without drinking water. Otters, dolphins, whales, and seals have adaptations that let them live in the water.

Humans are mammals, too. They can live almost anywhere on Earth. Humans learn how to adjust. You can live in the cold of the Arctic or the heat of a jungle by wearing the proper clothing. You can even live underwater in a submarine! You can breathe underwater with scuba tanks.

WHAT ARE THE MAIN KINDS OF MAMMALS?

Scientists put mammals into three main groups called monotremes, marsupials, and placentals. Monotremes and most marsupials live in Australia and on islands near Australia.

Monotremes are mammals that lay eggs. The duck-billed platypus and two kinds of spiny anteaters are the only monotremes.

Kangaroos, koalas, and wombats are marsupials. Marsupials give birth to babies that are not fully developed. The newborns climb into a pouch on their mother’s stomach. They stay in the pouch and drink mother’s milk until they finish growing. There are 250 kinds of marsupials.

All other mammals are placentals. You are a placental mammal. Like all placentals, you stayed inside your mother’s body until you were ready to be born. You were warm and safe, attached to an organ called the placenta. The placenta takes food from the mother's blood and gives it to the unborn baby.

Rats, mice, squirrels, and other rodents are the largest group of placental mammals. There are about 1,500 species of rodents. Bats, the only flying mammals, make up another big group of placentals. There are about 1,000 species of bats.

The smartest mammals are primates. Scientists group such animals as apes, monkeys, lemurs, and humans as primates. Humans are the smartest primates.

WHICH MAMMALS ARE PLANT EATERS?

Some mammals eat only plants. Cows, horses, pigs, and goats are plant-eating farm animals. Another name for plant eater is herbivore. Many wild plant-eating mammals live on plains and grasslands. Buffalo, deer, and antelope are wild plant-eaters.

WHICH MAMMALS ARE MEAT EATERS?

Wolves and dogs and lions, tigers, and other cats are some of the mammals that eat only meat. Most mammals that live in water are also meat eaters.

Another name for meat-eating animals is carnivore. Carnivores usually hunt for their food.

Hyenas are carnivores that do not hunt. They eat animals that are already dead.

The smallest carnivores eat worms and insects. Shrews and hedgehogs are small carnivores.

WHICH MAMMALS EAT MEAT AND PLANTS?

Some mammals eat both animals and plants. Another name for animals that eat both animals and plants is omnivore. The brown rat and the opossum are examples of omnivores. Humans are omnivores. They eat meat, fish, vegetables, and fruit. Scientists group bears with carnivores, but most bears also eat nuts, leaves, and berries.

HOW DO MAMMALS MOVE?

Most mammals that live on land have four legs. They use all four legs to walk or run. The cheetah is the fastest mammal. It can reach speeds of 58 miles (93 kilometers) per hour while chasing prey.

Mammals that live in water have flippers instead of legs. Seals, whales, and dolphins use their flippers to swim.

Kangaroos use their two hind legs to hop from place to place. Humans stand up on two legs. You use your legs to walk, run, or jump. You use your arms and hands to hold tools and carry things. You use your fingers to type on a computer.

Source: Microsoft ® Encarta

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