Pterosaur, Pterosaurus which means "winged lizard" in Greek. Pterosaur was a prehistoric flying reptile that ranged in size from a few inches to over 40 feet. Pterosaurs had hollow bones, were lightly built, and had small bodies. They had large brains and good eyesight. Some pterosaurs had fur on their bodies, and some (like Pteranadon) had light-weight, bony crests on their heads that may have acted as a rudder when flying, or may have been a sexual characteristic. Pterosaur wings were covered by a leathery membrane. This thin but tough membrane stretched between their body, the top of their legs and their elongated fourth fingers, forming the structure of the wing. Claws protruded from the other fingers.