EFFECTS OF PALEOGENE CLIMATE CHANGE ON DIVERSITY, GEOGRAPHIC RANGE AND BODY SIZE IN VENERICARD BIVALVES ALONG THE U.S. GULF COASTAL PLAIN

This research examines the response of the bivalve genus Venericardia to dramatic climate change during the Paleogene, as recorded in Gulf Coastal Plain deposits. Evaluating the link between climate and evolutionary change in the fossil record offers a deep time perspective on biotic response to climate variation and may provide a basis for predicting the effects of modern climate change.

For this study, we compiled data on three aspects of venericard diversity and distribution during the Paleogene of the Gulf Coastal Plain: taxonomic diversity, geographic range, and body size. For the diversity and geographic range components of the study, global occurrence data were compiled at the species level from published monographs and the Paleobiology Database. Boundary-crosser methods were applied to stratigraphic range data to quantify species-level diversity. Occurrence data from the Gulf Coastal Plain were also assigned latitude and longitude coordinates and compiled within a GIS framework to examine whether geographic distribution shifted over time. For the body size component of the study, several hundred venericard specimens, representing 20 species from over 30 localities, were digitally photographed from museum collections. Photographs of right valves were taken in both interior and cross-sectional orientations and landmark data were collected for 13 landmarks using tpsDIG2. Body size for each specimen was calculated as the geometric mean of centroid size in each orientation, then body size was averaged across species and localities to quantify size trends through time. We then assessed the extent to which shifts in diversity, geographic distribution, and body size coincided with specific climate changes such as the Paleocene-Eocene Thermal Maximum.

Preliminary plots of change in centroid size over time appear to correlate with temperature changes during the Paleogene. The preliminary data document a statistically significant increase in overall body size with an increase in temperature, although larger sample sizes are needed to verify this result.