Fossils Do Not Substantially Improve, and May Even Harm, Estimates of Diversification Rate Heterogeneity.

This article evaluates the utility of the fossilized birth–death (FBD) model, which incorporates fossil data to estimate diversification rates in phylogenies, particularly focusing on its performance when applied to largely modern trees. It highlights a critical distinction in the FBD model between two fossil types: m fossils (extinct lineages without sampled descendants) and k fossils (fossils ancestral to sampled descendants), noting that undersampling k fossils can bias parameter estimates, often inflating extinction and turnover rates. Through simulations using both individual fossils and stratigraphic ranges, the study finds that including fossils generally improves precision but not bias in diversification rate estimates, and that converting fossils to stratigraphic ranges tends to underestimate turnover and extinction fractions. Overall, the findings suggest that while fossils remain essential for understanding deep-time macroevolution, their inclusion in diversification analyses of extant-focused phylogenies provides limited benefit and can sometimes worsen inference accuracy, especially when fossil sampling is incomplete or biased.