An order of mammals, commonly known as bats, in which the front limbs are modified as wings, thus making the chiropterans the only truly flying mammals. Bats form the second largest order of living mammals (18 families, 202 genera, 1116 species). They range from the limit of trees in the Northern Hemisphere to the southern tips of Africa, New Zealand, and South America, but most species are confined to the tropics. On many oceanic islands they are the only native land mammals.