At least 60 genera of pterosaurs have been found ranging in size from a small bird to wingspans in excess of 40 feet. The wings were thin membranes of skin, similar to the wings of bats, attached to the extremely long fourth finger of each arm and extending along the sides of the body. There is no fossil evidence of feathers.
Their bones were hollow and had openings at each end. Unlike typical reptiles, pterosaurs had a breastbone that was developed for the attachment of flight muscles and a brain that was more developed than comparable dinosaurs of similar sizes.
Most paleontologists now believe that pterosaurs were adapted for active flight, not just gliding as was earlier believed.