ALTERNATING MACROEVOLUTIONARY REGIMES: ARE ORGANISMAL TRAITS PREFERENTIALLY SELECTED OVER EMERGENT TRAITS DURING MASS EXTINCTIONS? (Invited Presentation)

Whether mass extinctions and their associated recoveries represent an intensification of background extinction and origination dynamics versus a separate macroevolutionary regime remains a central debate in evolutionary biology. Previous work indicates that the strength of selection with respect to geographic range, an emergent trait, decreases between background intervals and mass extinction events. The extent to which selectivity on organismal traits changes in magnitude or direction between background and mass extinctions and their associated recoveries has received less attention. The evolution of animal body size is an ideal process to test for differences in macroevolutionary regimes, as body size is easily determined, comparable across distantly related taxa, and scales with many other organismal traits. Using marine animal body size, we test for shifts in selectivity between background intervals and the “Big Five” mass extinction events using capture-mark-recapture models. Our body-size data cover 10,203 fossil marine animal genera spanning 10 Linnaean classes with occurrences ranging from Early Ordovician to Late Pleistocene (485 – 1 Mya). Most classes exhibit differences in both origination and extinction selectivity between background intervals and mass extinctions, with the direction of selectivity varying among classes and overall exhibiting stronger selectivity during mass extinctions and their recoveries. These results suggest that emergent traits are more important determinants of survival during background intervals whereas organismal traits are more important determinants of survival during mass extinctions. Thus, mass extinction events have shaped marine ecosystems and macroevolutionary trajectories because they strongly select on organismal biology.