Mammals include a terrific variety of species including ourselves, human beings. The dictionary definition of a mammal is “animal of class of warm blooded vertebrates characterised by secretion of milk to feed young”. That covers quite a few animals from wood mice to whales and many in between. One of the advantages of being a warm blooded mammal is that you don’t need to wait for the sun to warm you up before going into action. It also means that mammals can be found in just about any place on the planet where the climatic conditions aren’t too extreme. Mammals have adapted to their environments in many ways.
Sea living mammals like dolphins, whales, seals and walruses have evolved a thick layer of outer fat to protect themselves from the cold sea. Other mammals like bats have developed a different method of protecting themselves from the cold. They hibernate in caves and trees when winter comes and slow their body metabolism right down so they can survive the cold winter without having to go out looking for food which is very scarce.