The flying apparatus of pterosaurs comprised a membranous wing stretched between the fourth finger of the hand and the side of the body. The fifth finger was degenerate, and the first three were free of the wing. The
pteroid bone, unique to the pterosaur group, attached to the wrist and pointed toward the shoulder, also helped support the wing, and the wings were strengthened by numerous connective tissue fibers. There is no fossil evidence of feathers. Most researchers now believe that pterosaurs were adapted for active flight, not just gliding as was earlier believed. Their bones are large but hollow, and they possessed a keeled breastbone for the attachment of flying muscles. Debate continues regarding how pterosaurs moved when on the ground and how maneuverable they were in the air. Pterosaurs, unlike the flying dinosaur Archaeopteryx, were not ancestral to the birds but represented a wholly separate line of development. Like dinosaurs, pterosaurs were affected by the mass extinction at the end of the Cretaceous period.
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