BIOGEOGRAPHIC STABILITY OF BENTHIC MARINE MOLLUSKS ACROSS THE END-CRETACEOUS MASS EXTINCTION (Invited Presentation)

Analyses of marine biogeographic structure across the end-Cretaceous mass extinction show conflicting results; some indicate greater cosmopolitanism whereas others indicate increased provinciality. Understanding whether and why this extinction event, and perhaps others like it, influenced the structure of marine communities is important for understanding the effects of extinction on ecosystems and the processes that underpin early recovery. To quantify how marine biogeography changed across the end-Cretaceous mass extinction and assess underlying causes, we downloaded fossil occurrence data from the Paleobiology Database, and selected for the 1,000 genera and 12,386 fossil occurrences of classes Bivalvia and Gastropoda from the Maastrichtian (~72.1 - 66 Ma) and Danian (~66.1 - 61.6 Ma) ages. The structure of taxonomic similarity was measured as a function of distance on a global grid of 812 equal-area (~630,000 km²) hexagonal cells using the Czekanowski and Jaccard coefficients, which each measure taxonomic similarity on a scale from 0 (totally endemic) and 1(totally widespread). We find no evidence for significant change in overall similarity or the relationship between similarity and distance in these data, whether measured across the combined dataset, each class individually, or when analyzing changes in biogeographic structure for surviving genera alone. The results are also not sensitive to the minimum number of occurrences set for the inclusion of geographic cells in the analysis. These findings indicate that the mass extinction did not result in any ecological release on the geographic ranges of marine genera, nor does any environmental change appear to have caused either increased or decreased environmental heterogeneity at a scale that would shift global biogeographic patterns.