A mammal is a warm-blooded animal whose young are born alive and fed with mother’s milk. Strangely enough, there are quite a few creatures who live in the sea who are mammals.

A zoologist groups these creatures under the name “Cetaceans.” They include the whales, the porpoises, and the dolphins. By studying their skeletons and other parts, we can determine that the ancestors of these animals lived on land in very ancient times.