When the dinosaurs were wiped out, it gave a group of small, warm-blooded animals the chance they needed to thrive. These were the mammals, distinct from other animals largely because they feed their young on milk. There are now around 5,000 species of mammal. They are grouped into different families and orders, including:
Marsupials are a group of mammals found in Australasia and the Americas. They give birth to tiny, undeveloped young. Many marsupials have a pouch. The newborn crawls into the pouch to feed on milk and complete its development.
Bats are the only mammals that can fly (rather than glide). They include the world’s smallest mammal, Kitti’s hog-nosed bat. Their wings are formed from a double layer of skin.
There are more species of rodent than any other mammal. Most rodents are small and many, such as mice, have a long tail. They all have clawed feet, long whiskers, and large gnawing teeth (incisors) at the front of their mouths.
Nearly all the members of this family of mammals are meat-eaters. They all share certain features, such as sharp cheek teeth for slicing flesh. Most are intelligent animals and many are ruthless killers.
Most hoofed mammals walk and run on the tips of their toes on hooves, which are simply large, heavy duty toenails. This is a large and varied group, and all are herbivores. They are also known as “ungulates.” They include deer, zebras, giraffes, and camels.
Although whales and dolphins spend their lives in water, they have to come to the surface to breath air; they have lungs, just like other mammals.
■ Brain box: All mammals have a large brain relative to their body size. The brain is protected in a hard skull.
■ Hair: Most mammals have hair or fur on their skin to keep them warm.
■Young: Rather than laying eggs, most mammals give birth to babies and look after them while they grow and learn.