Using avian bone histology to trace back the evolution of flight-related locomotor ontogeny in the dinosaur–bird transition

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The evolutionary success of the most diverse group of land vertebrates, birds, largely lies in their ability to fly. Spectacular fossils have demonstrated that birds are paravian dinosaurs; the only representatives to survive the end-Cretaceous mass extinction. Extinct paravians close to the dinosaur–bird transition show diverse skeletal and plumage morphologies, suggesting substantial variability in aerial skills. However, locomotor skills (e.g. running, flying) and related morphologies can change drastically through ontogeny in modern birds depending on the developmental strategy followed along the precocial (functional maturity at hatching, including various degrees of locomotor capability) to altricial (functional immaturity with embryo-like hatchlings) spectrum. This ontogenetic aspect of flight remains elusive in extinct bird-like dinosaurs, greatly encumbering research on flight origins. We aim to explore for the first time how bone tissue reflects precocial and altricial locomotor development, including the ontogenetic onset of powered flight, by studying limb bone shafts of growth series of modern birds, and apply these findings to bird-like dinosaurs. We will test correlation in a phylogenetic context between quantified limb bone histological traits and different developmental strategies in birds using thin sections and µCT data. These will provide a firm baseline for fossil inferences using the same approach and will generate a step-change in understanding the ontogenetic factor in the evolution of flight through the dinosaur to bird transition. The experienced researcher and hosts will bring together and integrate respective expertise in biology and palaeontology to deliver this highly innovative, timely, and multidisciplinary project that will broaden our view on how birds have mastered the skies for the last 150 million years.