Giant pterosaurs and the limits of animal flight (13.3)

Abstract

Pterosaurs appear to have had a particular propensity for the evolution of large size compared with other flying animals: at least eight genera of pterosaurs included species with wingspans in excess of 4 meters. I present a launch constraints model that accurately predicts size trends in pterosaurs. Azhdarchid pterosaurs evolved a suite of traits associated with improved terrestrial ability and rapid launch, including an expanded and curved deltopectoral crest, expanded coracoid flange, elongate metacarpal IV, and a reinforced fourth metacarpal‐phalangeal joint. This pattern explains why the largest pterosaurs were members of the Azhdarchidae. Most other “giant” pterosaurs were marine, and may have been more constrained in size than azhdarchids as a result of water launching requirements. Large marine pterosaurs, such as anhanguerids, tended to possess an expanded scapula, reinforced scapular‐notarial joint, warped deltopectoral crest, exceptionally broad wing pivot joint, expanded posterior brachial musculature, and reduced hind limbs. These traits are predicted as specializations to water launching. Pneumaticity, forelimb hypertrophy, and quadrupedal launch, combined with selection for low energy loitering and/or extended range, explains the repeated evolution of large size in pterosaurs.