Were dinosaurs doomed to extinction? New insights from phylodynamic models

Non-avian dinosaurs died out at the end of the Cretaceous period, coincident with the Chicxulub asteroid impact, at 66 Ma. However, how their diversity changed over the course of their preceding 180-million-year history is less well understood, and previous analyses have reached conflicting conclusions about the evolutionary trajectory of dinosaurs before their final extinction. This is, in large part, due to their highly fragmentary fossil record. Phylogenetic trees depicting evolutionary relationships provide additional information, including capturing a portion of lineage history that is otherwise not observable from fossil occurrence data. We investigated whether dinosaurs were declining in diversity during the latest Cretaceous using a phylodynamic modelling approach, which is more explicit and transparent than previous approaches, especially with respect to the assumptions made about how the dinosaur fossil record has been sampled. Using two alternative models, we show that based on available phylogenies we cannot currently reach a definitive conclusion about dinosaur diversification during the Cretaceous. More densely-sampled and accurate fossil timetrees, as well as models that capture more information about the quality of the dinosaur fossil record, may help to solve this debate.