Air-borne and acquatic mammals

Most mammals are firmly based on the ground or in the trees. Some can glide from tree to tree on outstretched flaps of skin, but only the bats can really fly. Their wings are supported on long fingers and run along the side of the body to take in the back legs and tails well. They are nocturnal and find their way about by echolocation – sending out high pitched sounds and listening for the echoes coming back from nearby objects. They can pick up the echoes from flying insects which enables them to change course to catch them.
Many mammals live in water, but most have to return to land to breed. Only the whales and sea cows are fully adapted for life in the water. Their front limbs form flippers and their tails form lobe like flukes. Hind limbs are absent, apart from some skeletal remains inside the body. The animals mate and give birth in water, and the only thing that indicates a terrestrial origin is that they still breathe air.