New insights into the crown age of angiosperms based on Bayesian tip and node dating

The timing of the origin of angiosperms and how they rapidly diversified into the dominant plant life on Earth, with diverse morphologies, has been the focus of numerous studies. In recent years, the rapid development of molecular clock methodology has provided an opportunity to answer this conundrum. In particular, how to best calibrate the molecular clock using the fossil record has received much attention. In this study, we apply Bayesian node and tip dating approaches that differ in how the calibration is achieved to estimate the crown age of angiosperms. Our extensive taxon sampling representing 67% of the families and 91% of the orders of extant angiosperms allows us to use the rich fossil record for divergence time estimation. Bayesian node-dating analyses with different calibration strategies emphasize that the posterior distribution is strongly constrained by the marginal prior at the node of crown angiosperms, and suggest that underlying assumptions of the fossil record shape the age of crown-group angiosperms. By assessing the sensitivity of fossilized birth-death tip dating, we reveal that fossils assigned to outgroups and the oldest fossils play a significant role in time estimates. Our tip dating analyses indicate an early Permian to late Triassic (282–226 Ma) origin for angiosperms and lay the foundation for further investigations into the origin and evolution of angiosperm traits and how they became dominant in terrestrial environments.