Biology: Mammals

Source: National Geographic

All mammals are endothermic vertebrates with a four-chambered heart, and skin covered with fur or hair. The young of most mammals are born alive, and every young mammal is fed with milk produced in its mother's body. In addition, mammals have teeth of different shapes that are adapted to their diets.

Fur and Hair

Source: Animals Australia 

All mammals have fur or hair at some point in their lives.
Fur and hair help mammals maintain a stable body temperature in cold weather.

Mammals are endotherms, which means that their bodies produce enough heat to maintain a stable body temperature regardless of the temperature of their environment.

Teeth

Source: National Geographic

Endotherms need a lot of energy to maintain their body temperature, and that energy comes from food. Mammals' teeth are adapted to chew their food, breaking it into small bits that make digestion easier.

Most mammals have teeth with four different shapes. Incisors are flat-edged teeth used to bite off and cut parts of food. Canines are sharply pointed teeth that stab food and tear into it. Premolars and molars grind and shred food into tiny bits.

Getting Oxygen to Cells

All mammals breathe with lungs.

Mammals breathe in and out because of the combined action of rib muscles and large muscle called the diaphragm located at the bottom of the chest.

Mammals have a four-chambered heart and a two loop circulation. One loop pumps oxygen-poor blood from the heart to the lungs and then back to the heart. The second loop pumps oxygen-rich blood from the heart to the tissues of the mammal's body, and then back to the heart.

Nervous System and Senses

The nervous system and senses of an animal receive information about its environment and coordinate the animal's movements. The brains of mammals enable them to learn, remember, and behave in complex ways.

The senses of mammals are highly developed and adapted for the ways that individual species live.

Most mammals have good hearing.

Most mammals have highly developed senses of smell.

Movement

Source: Animal Ark

One function of a mammal's nervous system is to direct and coordinate complex movement.

Reproducing and Caring for Young

Mammals have internal fertilization. Although a few kinds of mammals lay shelled eggs, the young of most mammals develop within their mothers' bodies and are never enclosed in an eggshell. All mammals, even those that lay eggs, feed their young with  milk produced in mammary glands.

Young mammals are usually quite helpless for a long time after being born.

Stay with their mother or both parents for an extended time.