The origin of avian flight: finding common ground

Few topics in evolutionary biology have been as controversial as the debate over the origin of avian flight. Although significant progress has been made in understanding how dinosaurs acquired flight, the debate remains mired in historical perspectives that prevent progress. We would like to renew the call to set aside the arboreal-cursorial debate and to draw attention to the common ground shared by both sides. To this end, we propose the following starting points: (1) Paravian dinosaurs were bipedal, with decoupled but complementary hindlimb and forelimb locomotion. (2) They had feathers on their body, their wings and in many cases their legs, that were probably highly plastic and multi-functional. (3) Paravians inhabited complex, three-dimensional environments that required proficiency in a variety of behaviours to negotiate. (4) Once the incipient wing form existed, asymmetric and symmetric flapping and possibly static wing postures served a variety of aerodynamic purposes that enhanced fitness. Taken together, these tenets conjure an exciting portrait of a dynamic organism adept at navigating through a complex environment with its versatile, incipient wings.