The inseparability of sampling and time and its influence on attempts to unify the molecular and fossil records

Abstract: The two major approaches to studying macroevolution in deep time are the fossil record and reconstructed relationships among extant taxa from molecular data. Results based on one approach sometimes conflict with those based on the other, with inconsistencies often attributed to inherent flaws of one (or the other) data source. What is unquestionable is that both the molecular and fossil records are limited reflections of the same evolutionary history, and any contradiction between them represents a failure of our existing models to explain the patterns we observe. Fortunately, the different limitations of each record provide an opportunity to test or calibrate the other, and new methodological developments leverage both records simultaneously. However, we must reckon with the distinct relationships between sampling and time in the fossil record and molecular phylogenies. These differences impact our recognition of baselines, and the analytical incorporation of age estimate uncertainty. These differences in perspective also influence how different practitioners view the past and evolutionary time itself, bearing important implications for the generality of methodological advancements, and differences in the philosophical approach to macroevolutionary theory across fields.