Athletic capability index in pterosaurs: an initial assessment

Pterosaurs had a unique morphology among flying vertebrates, and therefore, a direct comparison with living vertebrates regarding their terrestrial locomotion is impossible. In this study, we used the athletic capability indexes to infer aspects of the terrestrial proficiency of pterosaurs. We estimated the body mass, bending strength, and stylopodial axial strength indexes of 25 specimens of non-pterodactyloid and pterodactyloid pterosaurs. We used linear regression models to investigate the relationships between the indexes of athletic capability and the two stylopodia, and the indexes of athletic capability and the body mass of pterosaurs. We also compared the values of the index with those of other extinct and living animals. The results show higher values of the indexes of athletic capability for the humerus than the femur, indicating a higher relative strength of the forelimbs compared to the hindlimbs for bending and axial compression forces. We also detected a negative relationship between both indexes of athletic capability and body mass. Comparing the pterosaur athletic capability with other quadruped vertebrates indicates they had a good proficiency for terrestrial locomotion, even for plesiomorphic forms previously thought to have limited terrestrial locomotion. Even so, pteranodontoids are found to exhibit lower femoral ACI if compared to similar-sized pterodactyloids, notably azhdarchoids and dsungaripterids.