Life on earth is sustained by reproduction. There is so much diversity in reproduction too. The way in which a chick comes to life is different from the way a calf is born. Mammals are those animals that deliver young ones, and breast feed them.
Mammals are one of the six main classes of animals. These classes are categories of animals that scientists consider to be alike in some important ways.
A mammal is placed at the highest level of vertebrates, animals that have a backbone and a spinal cord. Human beings are mammals too. All female mammals give birth to live babies, with the exception of the platypus duck and the spiny anteater, which reproduce by laying eggs. However, regardless of how their babies are born, all female mammals nurse their young with milk, which they produce from special glands called the mammary glands.
Another important characteristic of mammals is their lungs. They breathe in air for oxygen supply in their bodies. A mammal is warm-blooded. This means that their bodies are built to maintain just about the same temperature all the time. Warm-blood allows the mammals to be very active and live in a wide variety of places.
Most mammals are covered either partially or completely with hair or fur. There are about 5000 types of mammals, including chimpanzees, elephants, bears, horses, pigs, bats, camels, mules, dogs and cats.
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