The multiple origins of powered flight among paravian theropod dinosaurs: constraints from new phylogenetic, aerodynamic and anatomical data

Abstract

The evolution of birds (Avialae) from paravian theropods is a textbook evolutionary radiation. Our understanding of this transition has been frustrated, however, by lack of consensus on the relationships between birds and their closest relatives. This lack of consensus has made it difficult to understand the timing and sequence of evolutionary changes along the line of descent to modern birds, particularly those involved with flight. We have addressed this issue through a larger, more resolved evolutionary hypothesis produced by analysing a revised dataset using an automated pipeline of analysis tailored to large morphological datasets. The grouping of dromaeosaurids and troodontids (Deinonychosauria) as the sister taxon to birds is corroborated, and we recover the Chinese ‘Jianchang’ paravians (e.g. Anchiornis) as the basalmost avialans, instead of troodontids. Wing loading and specific lift (theoretical and in vivo based criteria devised to discern volant from flightless avians) calculated for taxa with vanned feathers and interpreted in the context of the improved phylogeny provide upper and lower bounds for flapping-based locomotor evolution, especially powered flight. Powered flight appears to be limited to paravians and originated multiple times, with the strongest non-avialan candidates for this behaviour being the dromaeosaurids Microraptor and Rahonavis.