JANUS · A Tale of Survival and Diversification: Clarifying the earliest stages of modern bird evolutionary history

Living birds constitute the only lineage of dinosaurs that survived the Cretaceous-Paleogene Mass Extinction (K-Pg). However, whether specific aspects of their morphology and ecology facilitated their survival and subsequent radiation in the wake of the K-Pg still represents a major knowledge gap in avian palaeontology and macroevolution. Insights into this crucial evolutionary transition remain elusive, primarily due to the lack of an integrated approach that combines data from both Cretaceous and Cenozoic fossil birds. JANUS aims to overcome these outstanding limitations by building a novel dataset of fossil specimens spanning this transition to explore the origin of Neornithes (living birds) and using these to quantitatively explore the major macroevolutionary and ecological trends underpinning the early evolution of the group. This effort will rely on the collection of an unprecedentedly large sample of fossil bird three-dimensional micro–Computerized Tomography (CT) data, including Late Cretaceous and early Cenozoic birds from main European museums. This rich 3D morphological data will clarify the phylogenetic structure underlying the early evolution of modern birds through the assemblage of a novel phylogenetic dataset, leading to updated and time-calibrated hypotheses of the interrelationships among the earliest fossil representatives of the main neornithine lineages. Furthermore, this wealth of 3D CT data will enable the implementation of high-dimensional Geometric Morphometric analyses studying the relation between shape and ecology in fossil and living birds. The novel phylogenetic and eco-morphological framework will ultimately permit the application of a range of Phylogenetic Comparative Methods to evaluate ecomorphological signal across Cenozoic bird diversification, predict the likely ecology of ancestral birds, and characterise the large-scale macroevolutionary patterns structuring and impacting the extraordinary diversity of living birds.