THE EFFECT OF CALCITE AND ARAGONITE SEA TRANSITIONS ON BIVALVE BIOMINERALOGY

Recent research has shown much progress determining the impacts that fluctuating ocean chemistry displays toward certain calcifying and hyper-calcifying marine invertebrates during Calcite/Aragonite sea shifts. However, there continues some ambiguity regarding the effect of these transitions on bivalve biomineralogy. Here we test whether these oceanographic transitions affect the diversification, origination, and extinction rates of bivalves during the Mississippian and Jurassic Calcite and Aragonite Seas transitions. We accessed the Paleobiology Database to compare and contrast taphonomic occurrence data for aragonitic and bimineralic bivalve taxonomic groups. Data was constrained temporally to 11 million year bins spanning approximately 50 my before and after each calcite/aragonite transition during the Mississippian and Jurassic. We included all modes of preservation, global geographic scale, all marine depositional environments, and all possible lithologies. During the Mississippian transition from Calcite to Aragonite Seas, we predicted that aragonitic bivalve taxa would display heightened origination rates, diminished extinction rates, and a net increase in diversity, with bimineralic taxa displaying the reverse pattern. We expected opposite dynamics during the Jurassic transition to Calcite Seas conditions.

In contrast to these predictions, diversity in both aragonitic and bimineralic bivalve taxa was generally similar across the transition boundary. Similarly, there were little differences in origination and extinction rates, although these metrics are generally more likely to display interpretable patterns. For example, a weak pattern of increased diversification and reduced extinction rates in aragonite bivalve taxa was possibly present during the Mississippian transition. These results confirm previous studies that propose bivalves and other mollusks were physiologically or biomineralogically buffered from such oceanographic conditions.