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Three-dimensional geometry of a pterosaur wing skeleton, and its implications for aerial and terrestrial locomotion
This study reports on the three-dimensional spatial arrangement and movements of the skeleton of Anhanguera santanae (Pterodactyloidea: Ornithocheiridae), determined using exceptionally well-preserved uncrushed fossil material, and a rigid-body method for analysing the joints of extinct animals. The geometric results of this analysis suggest that the ornithocheirids were inherently unstable in pitch and yaw. As a result, pitch control would probably have been brought about by direct adjustment of the angle of attack of the wing, by raising or lowering the trailing edge from the root using the legs if, as is indicated in soft-tissue specimens of a number of unrelated pterosaur species, the legs were attached to the main wing membrane, or by using long-axis rotations at the shoulder or wrist to raise and lower the trailing edge from the wingtip. An analysis of the three-dimensional morphology of the wrist lends support to the idea that the pteroid – a long, slender wrist bone unique to pterosaurs that supported a membranous forewing – was directed forwards in flight, not towards the body. As a result, the forewing could have fulfilled the function of an air-brake and high-lift device, and may also have had an important role in pitch, yaw, and roll control. The joint analysis is consistent with a semi-erect quadrupedal model of terrestrial locomotion in the ornithocheirids.