Mammals (along with birds, fish, reptiles and amphibians) are vertebrate animals. This means they have a skeleton (made of bone or cartilage) and a backbone which is known as the ‘vertebrate column’. Mammals are unique from other vertebrate animals because females produce milk to feed their young from special glands called ‘mammary glands’. These glands give mammals their name. Mammals are warm blooded or ‘endothermic’ animals which mean they generate heat from within their own bodies. Some of our best-known and most loved wild creatures are mammals and they live in very different ways. Hedgehogs, red squirrels and moles are found on land. Whales, dolphins and seals are mammals that live in the sea and bats are small, furry mammals that fly at night. All mammals possess hair. Even baby whales are born with a moustache. Mammals are the only creatures that have a diaphragm. The study of mammals is called mammalogy.