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

Abstract

The evolution of birds from paravian theropod dinosaurs is a classic evolutionary radiation. Unfortunately, there is a lack of consensus on the geneology of birds and their very closest relatives. This 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 phylogeny produced by analysing a revised dataset using an automated pipeline of analysis tailored to large morphological datasets. The enhanced automation and newly developed techniques of this analytical pipeline should greatly increase access to more in-depth analyses using parsimony as a criterion for phylogenetic inference. We corroborate the grouping of dromaeosaurids and troodontids (Deinonychosauria) as the sister group to birds. We also recover the basal ‘Jianchang’ paravians as the basalmost avialans (Anchiornithidae e.g. Anchiornis), instead of troodontids. Wing loading and specific lift (theoretical and in vivo based criteria devised to discern volant from flightless avians) were calculated for taxa with vanned feathers and interpreted in the context of the improved phylogeny. This provided upper and lower bounds for flappingbased locomotor evolution, especially powered flight. Our results show that theropod powered flight appears to be limited to paravians and originated multiple times. The dromaeosaurids Microraptor and Rahonavis are especially strong non-avialan candidates for this behaviour.