Mammals have been named so because of their mammary glands. The females secrete milk from their mammary glands to feed their young ones. Milk is the natural food for new born mammals.

Like birds, mammals have also descended from reptiles, but along a different line. Like birds, mammals are warm blooded and breathe with the help of lungs. Mammals have hair to protect their bodies from cold, with the help of lungs.

Mammals have hair to protect their bodies from cold, with the exception of whale and hippopotamus, which have hardly any hair. Mammals have sweat glands which help to get rid of body waste, cooling the body in the process.

The shape and number of the teeth in mammals show great diversity and are related to their diet.

The mammals are the only vertebrates to possess a diaphragm, which is a muscular membrane dividing the chest cavity and the abdominal cavity.

The brain of mammals is more highly organized than any other animal. It is very developed and large.

Mammals give birth to their young, which develop in a cavity inside the mother’s body. There are some exceptions like the platypus and the spiny anteater. They are the link with the reptiles from with the reptiles from which mammals have evolved. These animals lay eggs unlike the other mammals.