Pteranodon is a pterosaur, and like the other most famous member of the (smaller) pterosaurs, Pterodactylus, it had a wing that was held open by a single elongated digit. That digit allowed for a wing that was approximately 5.6 metres (18 ft) in males and 3.8 metres (12 ft) in females. These dimensions allowed for enormous surface areas and, despite their large reptilian bodies, were more than enough to keep aloft the extremely light Pteranodon. That may seem like a confusion of terms, but the large reptilian bodies of Pteranodon were composed of light skeletal elements, similar to those of bats and birds in their general composition and pneumatic properties, though definitely different enough that three should never be confused if presented in isolation. Even the elongate crests on the backs of Pteranodon skulls are pneumatic and lightweight, allowing the flying reptile to move its head about while in flight without changing its center of mass significantly. Debate has ebbed and flowed about the purpose of the crest beyond sexual dimorphism and has included ideas such as rudder control during flight. This would be an interesting and not unrealistic use of the crest, but I cannot claim to know its morphology well enough to present either side of the argument with an assertive conviction. Personally, I think the wings were soaring devices and would to imagine that they crest was used to impress the ladies and to aid in steep banking turns, but more proof of that concept is certainly in need. Unfortunately, due to their lightweight skeletons Pteranodon tend to be preserved in slabs of very flat stature and with little to no soft tissue imprints aside from the wings.