Neuroanatomical convergence between pterosaurs and non-avian paravians in the evolution of flight

Abstract

The oldest known pterosaurs lived approximately 220 million years ago1 and were already animals capable of powered flight,2 an ability that later evolved independently among paravian dinosaurs, the group that includes living birds and their closest non-avian relatives.3 Flight is a complex locomotory mode that requires physiological adaptations4 and a dramatic transformation of the body plan, including changes in body proportions, specialized integument, and acquisition of novel neurosensory capabilities.5 Although pterosaurs and birds developed distinct skeletal and integumentary adaptations for flight, they are hypothesized to share neuroanatomical traits linked to aerial locomotion.6–9 Here, we use geometric morphometrics and phylogenetically informed analyses to assess the origin and evolution of brain shape and size in pterosaurs, tracing the transformation from their non-volant closest relatives (lagerpetids), and compare their trajectory with that in the dinosaur-bird transition. Pterosaurs have globular brains with moderately enlarged hemispheres, more closely resembling non-avian paravians such as troodontids and Archaeopteryx lithographica than living birds. Whereas birds inherited their basic brain structure from their dinosaurian ancestors,10–17 pterosaurs share only the ventrolateralization of the optic lobe with their closest non-volant relatives, the lagerpetids. This suggests that, in contrast to the bird-line archosaurs, where exaptation may have played a central role in the stepwise assembly of the avian brain configuration, brain evolution in pterosaurs seems to have unfolded rapidly at the origin of flight.