Powered flight potential approached by wide range of close avian relatives but achieved selectively

Abstract

Evolution of birds from non-flying theropod dinosaurs is a classic evolutionary transition, but a deeper understanding of early flight has been frustrated by disagreement on the relationships between birds (Avialae) and their closest theropod relatives. We address this through a larger, more resolved evolutionary hypothesis produced by a novel automated analysis pipeline tailored for large morphological datasets. We corroborate the grouping of dromaeosaurids + troodontids (Deinonychosauria) as the sister taxon to birds (Paraves), as well as the recovery of Anchiornithidae as basalmost avialans. Using these phylogenetic results and available data for vaned feathered paravians, maximum and minimum estimates of wing loading and specific lift calculated using ancestral state reconstruction analysis are used as proxies for the potential for powered flight through this transition. We found a broad range of paravian ancestors with estimates approaching values that are indicative of powered flight potential. This suggests that prior to the evolution of flight there was a wider extent of experimentation with wing-assisted locomotion among paravians than previously appreciated. We recovered wing loading and specific lift estimates indicating the potential for powered flight among fossil birds as well as unenlagiine and microraptorine dromaeosaurids. In the context of our phylogeny and of Mesozoic palaeogeography, our results suggest that the potential for powered flight originated three or more times from a broad range of ancestors already nearing this potential, providing a well-supported scenario for the origin of theropod flight to further explore.The origin of birds (Avialae) and modern powered flapping flight were iconic events in the history of life. Recent studies of early birds and their closest dinosaurian relatives (non-avialan paravian theropods) have provided key insights into this major evolutionary transition. It is now clear that anatomies and behaviours traditionally associated with birds were first acquired by non-avialan dinosaurs before the origin of birds and modern powered flapping flight. These include smaller body size, accelerated evolutionary rates 1-3 , early feathers of 'modern' aspect 4-17 , complex plumage colouration, flapping-based

Trophic shift and the origin of birds

“…Early birds, such as Archaeopteryx and Jeholornis, are believed to be primarily arboreal and capable of gliding flight, which are believed to be descended from maniraptorans that had already evolved gliding flight (Xu et al 2003;Benton 2015;Chatterjee 2015). Indeed, many maniraptorans possess asymmetric flight feathers to generate lift, and in particular, the discovery of many bird-like paravians, such as Microraptor, Anchiornis, Xiaotingia, and Aurorornis, is the most unusual in developing four wings, suggesting their possible high performance of gliding flight (Benton 2015;Chatterjee 2015;Pei et al 2020). However, given the diet divergence between non-avian maniraptorans and ancestral birds, and particularly that many of gliding maniraptorans (e.g., Microraptor and Sinornithosaurus) were potential predators of early birds (Gong et al (Fig.…”

Evolution: Brainier Birds

“…Like many other traits, such as feathers, wishbones and pneumatic skeletons, that are interpreted as adaptations for flight, early birds inherited brains from ancestors that were sufficiently large to achieve aerial locomotion [8]. In fact, one of the more dramatic grade shifts in brain size found by Ksepka and colleagues [1] occurred in Paraves, the taxonomic group that encompasses birds and a few other lineages of predominantly small, feathered dinosaurs, such as dromaeosaurs, some of which may have evolved flight independent of birds [9]. A novel finding, however, is that brain-tobody size scaling was less constrained at the theropod-bird transition than in later stages of bird evolution, and marked by greater plasticity and higher evolutionary rates, likely setting the stage for the next major shift in bird brain evolution at the end of the Cretaceous.…”