Bats and most birds share the ability to fly by flapping their wings. One might assume that these two groups evolved from a common ancestor with wings. In fact, bats and birds are not closely related, and their last common ancestor was a ground-dwelling animal with four limbs. The evolution of wings is an example of convergent evolution—the independent evolution of similar features with comparable function. The ability to fly evolved multiple times, which is evident upon closer inspection of the morphology of wings in birds and bats. The hand and wrist bones of birds are fused, and feathers provide a large area to create lift. During flight, birds tuck their hindlimbs out of the way. In contrast, the finger bones of bats are elongated and mount a large area of skin that makes up the wing. The hindlimbs of bats play an essential role in creating the wing. Another example of convergent evolution can be found in whales and fishes. Whales are warm-blooded mammals that nurse their offspring and breathe air. Fish are ectotherms, lay eggs, and exchange gases using gills. However, the requirements of life in water led to the evolution of similar—or analogous—features in whales and fishes. Both groups have fins and a streamlined body form to more easily move through the water. Whales and fishes do not share a recent common ancestor, yet have analogous features with similar function due to convergent evolution.