THE IMPACT OF OAE2 ON GLOBAL MOLLUSCAN DIVERSITY DYNAMICS

Ocean Anoxic Events (OAEs) are periods in time when the earth’s ocean basins became largely or entirely depleted of dissolved oxygen. These periods lasted several million years in some cases and have contributed to major die-offs such as the End-Permian Mass Extinction. The middle Cretaceous is characterized by a series of OAEs; however, the biotic impact of these events is unclear. Utilizing the Paleobiology Database (PBDB), we analyzed both species and generic diversity of mollusks across the Bonarelli event (OAE2) at the Cenomanian-Turonian stage boundary. In order to test whether survivorship across the OAE was influenced by paleoecological factors, diversity data was collected within the parameters of faunality, mobility, and feeding strategy. Species and generic databases were sample-standardized, and diversity was statistically compared via a Mann-Whitney U. Significant unilateral diversity losses were observed when comparing both total diversity, and across all paleoecological contexts. The average percent losses were 37% and 47% when comparing the generic and species datasets respectively. Preliminary analysis of the influence of paleoecological factors on extinction indicates that semi-infaunal, facultatively mobile, and suspension feeding mollusks suffered the least diversity loss, whereas infaunal, actively mobile or stationary, and detritovorous taxa showed the greatest decline in diversity. In contrast to previous research suggesting that OAE2 only caused minor impacts to global diversity patterns, these results support the Bonarelli Event as a significant driver of extinctions in Molluscan taxa.