What are the characteristic features of mammals?

Characteristic features of mammals are:

Their body is covered with hair.

They are warm-blooded animals.

Their hearts are four-chambered.

They respire through the lungs.

Fertilization takes place internally.

Eyes are covered with eyelids.

External ear called ear-pinna is present.

Skin has sweat glands and sebaceous glands.

The body is divided into thorax and abdomen by a muscular diaphragm.

The above mentioned points define the characteristic features of mammals.