Pterosaurs
Pterosaurs are very closely related to dinosaurs, but they have evolved separately from previous dinosaurs. The oldest pterosaurs appeared about 215 million years ago in the Late Triassic and went away with other dinosaurs 65 million years ago (Unwin 2006).
The pterosaurs are divided into two groups: rhamphorhynchoids, which predominantly lived in the Triassic and Jurassic, are relatively small primitive pterosaurs that mostly have long and sparse teeth on the jaws, long tails, and relatively short necks. On the other hand, pterodactyloids, which predominantly proliferated in the Cretaceous, have narrow and long wings on the short tail, and many species have crests of various shapes and sizes. Teeth can vary from thick and short to long and dense like combs, and some like Pteranodon have completely lost them (Unwin 2006).
The pterosaur wing skeleton is hollow like a bird, but has dense supporting structures inside of it, so it is very light and sturdy. The wing membrane, which is reinforced with complex, tough fibers, is attached to the elongated fourth finger and the torso, and the area is wide enough for flying. Tightly built rib cage and thick muscles in the upper arm and the shoulder blade allow strong wing strokes. Because of these features, the pterosaurs could reduce the weight of the wing, glide for a long time even at low wind speed, and move agilely and explosively (Unwin 2006). The fact that hundreds of pterosaur fossils are found in marine sedimentary strata hundreds of kilometers offshore demonstrates their excellent long-range flight capability.
Two representative groups of pterosaursThe Late Cretaceous Pteranodon longiceps is short-tailed, large pterodactyloid pterosaurs with very large skulls (up to 1.8 m). The bone crests, which rose above their heads, would have been act as an airplane's tailfin during flight or as a decoration for attracting females' attention during the breeding season (ones with relatively large crests are assumed to be male).
Rhamphorhynchus muensteri is representative of small rhamphorhynchoid pterosaurs with a wing width of about 1 m and at least 200 to 300 specimens have been found in the Late Jurassic limestone layer where Archaeopteryx was found. Unlike Pteranodon, it features long tail and long, sparse teeth.
Pteranodon
Rhamphorhynchus
Pterosaurs successfully conquered the Mesozoic skies through a series of dramatic evolution, and their flying ability may have been almost as good as the birds or perhaps even better.
Wing structures of flying vertebrates
Thoughout the whole Earth's history, vertebrates that could fly by their own were reptilian pterosaurs, avian birds, and mammalian bats. All of them have evolved wings with forelimbs, but their wing structures are all different. Feathers for flights sprout on the front leg where fingers were fused together. Bats grew their second to fifth fingers, wing membranes forms between the fingers and body. The wings of the pterosaurs seem to be similar to those of the bats at first glance, but it is a unique wing made from membranes between the elongated fourth finger and the torso.