A MOLLUSCAN LATITUDINAL SELECTIVITY GRADIENT IN THE END-CRETACEOUS MASS EXTINCTION

There are few examples where survivorship across mass extinction clearly links to ecology. To test whether ecological organization affected survivorship in the Cretaceous-Paleogene (K-Pg) mass extinction, we used network methods to detect modular spatial patterns in a global Maastrichtian database of 329 bivalve genera. Modules, interpreted as biogeographically-organized, biome-level units, differed in extinction intensities (modular selectivity) across the K-Pg boundary. Though extinction intensity was geographically heterogeneous, it had no clear geographic signature. However, we detected a latitudinal gradient in the strength of selectivity for geographic range across modules. This suggests that modules at higher latitudes had lower extinction than expected given the geographic ranges of the genera, implying that high latitude biomes had less extinction risk ecologically, and/or the intensity of the K-Pg kill mechanism declined with distance from the tropics. Our results highlight the importance of macroecological structure in the determination of extinction risk of taxa.