Tip dating and Bayes factors provide insight into the divergences of crown bird clades across the end-Cretaceous mass extinction

Abstract

The origin of crown birds (Neornithes) remains contentious due to conflicting divergence time hypotheses obtained from alternative sources of data. The fossil record suggests limited diversification of Neornithes in the late Mesozoic and a substantial radiation in the aftermath of the Cretaceous-Paleogene (K–Pg) Mass Extinction, 66.02 million years ago. Molecular clock studies, however, have yielded estimates for neornithine origins ranging from the Early Cretaceous (~130 MYA) to ~72 MYA, less than 10 million years before the K–Pg. We use Bayes Factors to compare the fit of node ages from different molecular clock studies to an independent morphological dataset. Our results allow us to reject scenarios of crown bird origins deep in the Early Cretaceous, as well as an origin of crown birds within the last 10 million years of the Cretaceous. The scenario best supported by our analyses is one where Neornithes originated between the Early and Late Cretaceous (~ 100 MYA), while numerous divergences within major neoavian clades either span or postdate the K–Pg. This study affirms the importance of the K–Pg on the diversification of modern birds, and the potential of combined-evidence tip-dating analyses to illuminate recalcitrant “Rocks vs Clocks” debates.