Mammals are warm-blooded animals. They feed their newborn young with milk and protect them from danger during the earliest part of their lives. Most mammals develop inside the mother, instead of hatching from eggs. Except for some sea mammals, they all have four limbs and are covered with hair or fur. There are about 5000 species of mammal living on the land, in the water or in the air. They range in size from tiny shrews to giant blue whales. Mammals are the group of animals to which humans belong.

Senses

Mammals have large brains and highly developed senses. Human eyes can see in great detail and in a wide range of colours. With its superb hearing, a dog can detect sounds far higher in pitch than humans can, and hear sounds much further away.

A number of mammals rely on their sense of smell. A dog's is up to 40 times more sensitive than a human's. Scent may be used to mark the borders of a mammal's territory, or to detect an approaching predator.

All female mammals have mammary glands. These produce milk after their young are born. The young feed on this milk, which gives them all the nutrients they need until they are able to feed themselves. During the period of suckling (feeding on milk), the mother will protect them from predators.

Young mammals

All mammals, except the marsupials and monotremes, are born fully formed. Some, such as rabbits (and humans) are helpless as babies. They grow while in the safety of their burrow or den. Mammals that live in open spaces, such as horses, cattle or deer, are able to walk and even run a few minutes after birth. This is because they would need to be able to flee from from predators.

Many mammals live together in groups—sometimes a handful of animals, sometimes hundreds or even thousands. The group will often help to rear and protect the young. Carnivores such as lions, wolves or hyenas hunt together in packs. This enables them to kill larger animals than they could tackle alone. Herbivores, such as deer or cattle, form large herds that give them some protection against such predators.

Teeth

These skulls, pictured left, belong to four mammals that eat very different foods. Rats, kinds of rodent, have long, hard front teeth for gnawing nuts, seeds, fruits, leaves, bark or wood. The anteater has no teeth at all, just long jaws and an extremely long, sticky tongue for lapping up ants.

The grey wolf has strong jaws (the force of its bite enables it to crush bones) and sharp teeth for tearing through meat. Zebras have sharp front teeth to slice through grass stems, while their back teeth grind and chew the tough plant material.