Mammals live in almost every habitat on Earth. This includes habitats in polar regions, oceans and tropical forests. The survival of mammals in almost all environments is largely a result of their various adaptations.
Mammals possess characteristics that make them different from all other species. These include hair growth, mammary glands and ear bones. No other species have any of these characteristics.
All mammals at some point have hair growing on at least one area of their bodies. Fur, whiskers and defensive quills are all considered hair. Hair on mammals serves many different functions, from skin protection to camouflage to defense and insulation.
Mammals are the only species to nurse their babies with milk produced by mammary glands. Male and female mammals both have mammary glands, but they only develop enough to produce milk in females. The one exception to this rule is the Dayak fruit bat. The males have mammary glands that are fully developed, and they feed their young with milk produced by these glands.
All mammals have three bones in their inner ears that are arranged in a pattern that is unique to mammals. These three bones are called the incus, malleus and staples. These bones transmit sound vibrations to the inner ear.