Evolution of morphological disparity in pterosaurs

Pterosaurs were important flying vertebrates for most of the Mesozoic, from the Late Triassic to the end of the Cretaceous(225–65 Ma). They varied enormously through time in overall size (with wing spans from about 250 mm to about 12 m), andin features of their cranial and postcranial skeletons. Comparisons of disparity based on discrete cladistic characters showthat the basal paraphyletic rhamphorhynchoids (Triassic–Early Cretaceous) occupied a distinct, and relatively small, regionof morphospace compared to the derived pterodactyloids (Late Jurassic–Late Cretaceous). This separation is unexpected,especially in view of common constraints on anatomy caused by the requirements of flight. Pterodactyloid disparity shiftedthrough time, with different, small portions of morphospace occupied in the Late Jurassic and Late Cretaceous, and amuch larger portion in the Early Cretaceous. This explosion in disparity after 100 Ma of evolution is matched by thehighest diversity of the clade: evidently, pterosaurs express a rather ‘top heavy’ clade shape, and this is reflected in delayedmorphological evolution, again an unexpected finding. The expansion of disparity among pterodactyloids was comparableacross subclades: pairwise comparisons among the four pterodactyloid superfamilies show that, for the most part, theseclades display significant morphological separation, except in the case of Dsungaripteroidea and Azhdarchoidea. Finally,there is no evidence that rhamphorhynchoids as a whole were outcompeted by pterodactyloids, or that pterosaurs were drivento extinction by the rise of birds.