Meeting Abstract

86.4  Thursday, Jan. 7  How pterosaurs landed and why they evolved from bipedal ancestors PADIAN, Kevin*; MAZIN, Jean-Michel; BILLON-BRUYAT, Jean-Paul; Univ. of California, Berkeley; Univ. of Lyon1, France; Canton Jura, Switzerland kpadian@berkeley.edu

There is continued controversy about how pterosaurs, the flying reptiles of the Mesozoic Era, walked on land. Major bauplan changes occurred with the evolution of pterodactyloids, the clade that succeeded basal pterosaurs in the Late Jurassic – Early Cretaceous until the end of the Cretaceous. Quadrupedal pterodactyloid pterosaur tracks from the Late Jurassic show that the hindlimbs moved parasagittally, whereas the hypertrophied forelimbs could make tracks both close to the body wall and far outside it. A landing track from this locality, the first ever recorded, shows in detail how the animal flapped to stall, landed with a stutter-step, and ambled off. This sequence reflects their highly developed capacity for flight control and maneuverability. The origin of pterosaur locomotion on the ground has also long been questioned: notably, whether pterosaurs evolved from bipedal or quadrupedal ancestors. Most analyses have concluded that pterosaurs are basal ornithodirans, the sister group to dinosauromorphs. Phylogenetic analyses suggest that basal archosauromorphs were quadrupedal, whereas basal ornithodirans were bipedal. Morphometric comparisons suggest that basal pterosauromorphs were bipedal; that compared to their pseudosuchian outgroups their hindlimbs became longer than the trunk, and the forelimbs later lengthened as flight evolved. The forearm lengthened even faster than the humerus, and was usually one of the longest wing elements in non-pterodactyloids. Trackways also show that quadrupedal pterodactyloids modified their footfall patterns from the traditional reptilian condition, suggesting that the habit was secondary.