POSTURE, LOCOMOTION, AND PALEOECOLOGY OF PTEROSAURS

Abstract

Despite being studied for over 200 years, the posture, locomotion, paleobiology, and phylogeny of pterosaurs are still poorly understood due to lack of well-preserved, three-dimensional specimens. In this paper we investigate the posture, locomotion, and paleoecology of pterosaurs based on anatomy and biomechanics: how they walked, how they flew, and how they lived. We want to understand how evolution has adjusted their skeletal structures and movements to maximize performance. The limb joints of an exquisite skeleton of the Cretaceous pterodactyl Anhanguera piscator are analyzed to estimate the range of movement during terrestrial and aerial locomotion. On land, pterosaurs were quadrupedal knuckle walkers with laterally directed digitigrade manus and forwardly directed plantigrade pes. From this position, pterosaurs could stand on their rear legs and run bipedally in an upright posture for a short distance during takeoff and landing. Pterosaurs evolved two basic wing planforms over time: the basal "rhampho-rhynchoids" had broad wings in bat-like fashion where the patagium was attached to the ankle; in pterodactyloids, the wings became narrow and the patagium was anchored near the knee joint. The wingtips appear to have been more rounded to avoid stalling. The actinofibrils in the membrane would confer some stiffness to the wing to maintain a flatter camber, preventing it from billowing and tearing during flight. They would also facilitate the folding of the wing when not in use. The flight performance of pterosaurs is investigated using ten genera in a wide size spectrum during their 160 million years of evolution, where the body mass ranges from 0.015 kg to 70 kg and the wingspan from 0.4 m to 10.4 m.