Few of the characteristics of mammals are as follows-
1. They directly give birth to young ones.
2. They suckle young ones by means of mammary glands.
3. They have hair on their skin.
4. Sweat and oil glands are present.
5. They are warm blooded animals.
6. Their heart is 4-chambered - 2 auricles and 2 ventricles.
7. A muscular diaphragm separates the thorax and abdomen internally.
8. Breathing is by means of lungs.
9. They have a pair of external ears or pinnae.
10. They show presence of external testes contained in a scrotum (testicles).