A new approach to determining pterosaur body mass and its implications for pterosaur flight

Abstract

Efforts to establish the masses of pterosaurs have been attempted for almost a century, but the methods employed are often as problematic as their conclusions that pterosaurs are unusually lightweight. Historically, most pterosaur masses have been determined through geometric modelling of pterosaur bodies and extrapolation of body densities from modern birds. However, both ecology and fl ight style are known to induce variation of body density across modern bird species, casting doubt on this frequently used method. Here, a new approach to mass estimation is attempted that requires no assumption of soft tissue density or distribution: following observations that the relationship of dry skeletal mass to body mass is essentially identical in ecologically and phylogenetically disparate modern birds and mammals, the skeletal masses of 19 pterosaur taxa have been estimated and their body masses regressed from the relationship between skeletal mass and body mass in modern forms. Masses derived from this method are up to three times greater than those estimated in previous studies with the largest pterosaur in this investigation (wingspan 10 m) found to have a mass of 250 kg. Reappraisal of pterosaur masses shows that lightweight pterosaur mass estimates are considerably lower than those of similarly sized birds and bats, requiring inordinate amounts of pneumaticity (up to 90 per cent for the lowest estimates of the largest forms) and are wholly unrealistic in light of the enormous sizes achieved by some pterosaurs. Combining heavier mass data with restorations of pterosaur wings based on preserved wing membranes permits assessment of basic pterosaur fl ight characteristics. Preserved wing membranes suggest that ankle-attached brachiopatagia are the best supported pterosaur wing model, and distinctions in forelimb/hindlimb ratios produce a range of wing shapes despite a standardised brachiopatagia confi guration. Plotting greater masses and ankle-attached wings into a principal component analysis of aspect ratio and wing loading demonstrates that pterosaurs had a range of fl ight styles similar to those seen in modern volant vertebrates. A broad spectrum of pterosaur fl ight styles are predicted including marine and thermal soarers, adaptive generalists and forms for which fl ight is energetically costly and expensive.