Ad fontes: divergence-time estimation and the age of angiosperms.

Accurate divergence times are essential for interpreting and understanding the context in which lineages have evolved. Over the past several decades, debates have surrounded the discrepancies between the inferred molecular ages of crown angiosperms, often estimated from the Late Jurassic into the Permian, and the fossil record, placing angiosperms in the Early Cretaceous. That crown angiosperms could have emerged as early as the Permian or even the Triassic would have major implications for the paleoecological context of the origin of one of the most consequential clades in the tree of life. Here, we argue, and demonstrate through simulations, that the older ages inferred from molecular data and relaxed-clock models are misled by lineage-specific rate heterogeneity resulting from life history changes that occurred several times throughout the evolution of vascular plants. To overcome persistent discrepancies in age estimates, more biologically informed and realistic models should be developed, and our results should be considered in the context of their biological implications before we accept inferences that are a major departure from our strongest evidence.