People are mammals, and so are lions, elephants, whales, pigs and rabbits. How do we know? Well, scientists have sets of rules which tell them what sort of animals creatures are: whether they are mammals, fish, reptiles, amphibians, birds or insects. There are two things which tell the scientists that an animal is a mammal. Firstly, all mammals have some hair on their bodies, and secondly, all mammals have glands which produce milk for their babies to drink during the early stages of life. This word ‘mammary’ is what gives us the word ‘mammal’.
The whale, the dolphin and the porpoise may look like fish than mammals, but there is always some hair on their bodies, however small the amount, and they suckle their young with their own milk. The duck billed platypus is perhaps the strangest mammals of them all. It has a beak instead of lips, and it lays eggs rather than giving birth, like people do, to live young. But it is a mammal. After the babies are hatched, the platypus feeds its young with milk it produces itself, and as it also has body hair, we know that it is a mammal.