The external ear-flaps of many mammals aid hearing by concentrating sound waves.

   
  "It is only among mammals that ears become noticeable, even striking, because of the visible external ear-flaps behind the narrow opening of the outer ear tube…The most obvious use of the ear-flap, though not necessarily the most important, is to gather and concentrate sound waves." (Foy and Oxford Scientific Films 1982:167)
  Learn more about this functional adaptation.