DETERMINANTS OF PHANEROZOIC EXTINCTION: A META-ANALYSIS OF POST-ORDOVICIAN BIVALVE AND GASTROPOD SELECTIVITY

The extent to which species traits and environmental conditions interact to affect extinction selectivity is poorly understood. The fossil record provides a unique opportunity to explore this issue by examining traits, such as geographic range and life habit, in the well-preserved and documented molluscan record. Few attempts have been made, however, to quantitatively synthesize the extensive paleoecological literature on selectivity.

In this study, we use a meta-analytic framework to address the following questions: (1) What are the gross patterns of extinction selectivity with respect to geographic range and life habit in fossil bivalves and gastropods? (2) How does extinction rate affect the intensity and direction of extinction selectivity? and (3) How are the causal mechanisms of extinction reflected in patterns of selectivity? We examine bivalve and gastropod survivorship according to particular traits, including geographic range and life habit.

Using a database of 300+ effect sizes (i.e., comparisons of victims vs. survivors) compiled from over 30 sources published from 1973-present, we first summarize patterns of selectivity. We then test for relationships between extinction selectivity and causal mechanisms. Our study incorporates data on a variety of extinction events (from background to mass extinction events, Ordovician to Pleistocene) and a range of potential environmental correlates and causal mechanisms (including sea level change, δ¹⁸O, δ¹³C, flood basalt activity, and bolide impact events). Preliminary results suggest that selectivity against taxa with narrow geographic ranges occurs, but only during intervals of lowered sea level. Similarly, the relationship between life habit and survivorship is complex. Infaunal taxa are more likely to survive when δ¹⁸O values are high and less likely to survive when values are low.