ENVIRONMENTAL CHANGE AND THE SELECTIVITY OF LOCAL EXTINCTION: A CASE STUDY FROM THE LATE NEOGENE SAN JOAQUIN SEAWAY, CENTRAL-SOUTHERN CALIFORNIA

Analyses of past extinctions have the potential to shed light on the traits that will influence extinction risk during current and future global change. The excellent fossil record of marine mollusks is particularly suitable for such analyses. Broad-scale analyses have revealed relatively few consistent relationships between traits and extinction risk, but this may mask local-scale patterns that can be more directly tied to local environmental changes. The San Joaquin Basin in central-southern California presents an opportunity to study the dynamics of extinction and extirpation in a geographically limited mesocosm. The basin was flooded by the Pacific Ocean, creating the San Joaquin seaway, between 10 and 2 Ma. The environment of the San Joaquin Seaway was dynamic, characterized by large changes in freshwater input from rivers draining the nearby Sierran highlands and from tectonic and eustatically-driven changes in marine connectivity. Final closure of the seaway occurred between ~2.3 to ~2.0 Ma, marking the transition to a non-marine basin. Previous studies of the fossil record of the San Joaquin Seaway have revealed 7 distinct clusters of last occurrences apparently coinciding with eustatic sea level changes, but diversity changes have not been examined in a sampling standardized framework with respect to their sequence stratigraphic context. Using existing museum collections, we will compile a database of species occurrences and traits such as body size, feeding mode, larval ecology, substrate preference, and motility. We will use standard statistical approaches to evaluate the influence of traits such as on probability of last occurrence during multiple pulses.