Popular science asserts that after the extinction of the non-avian dinosaurs at the Cretaceous-Paleogene (K-Pg) boundary 66 million years ago, mammals rapidly diversified to fill newly empty ecological niches. Such adaptive radiation examples are common in biology text books and are based on a intuitive narrative: one speciose and group of organisms goes extinct allowing a less speciose group to diversify.

However, describing adaptive radiations and the ecological role of extinction is not so trivial. When looking at species diversity or morphological diversity (disparity), different stories start to emerge. In fact, such adaptive radiations are based on the idea of a link between diversity, disparity and ecological niches which can be non-straightforward. Furthermore it can be unclear how disparity should be measured as a metric, how to measure it through time, and how we can test changes in disparity (null models). In this talk I am going to discuss some methodological advances aiming to improve our understanding of changes in disparity-through-time. As with many “intuitive" evolutionary stories, a closer look at the effect of the K-Pg extinction on mammalian morphological diversity suggests mixed evidences for an adaptive radiation. Mammalian morphological diversification status: it's complicated.