PREDATOR-PREY INTERACTIONS AND SIZE-FREQUENCY DISTRIBUTIONS RECORDED IN MOLLUSCAN ASSEMBLAGES OF THE PLIO-PLEISTOCENE NASHUA FORMATION OF NORTHERN FLORIDA

The Nashua Formation represents a biogeographic gap in knowledge on fossiliferous deposits studied from the Plio-Pleistocene of the southeastern U.S. Previous work on extinction episodes in the region has indicated that patterns and changes in paleocommunities across the boundary vary with latitude requiring new data from under-sampled locations. Thus, a paleontology class research project commenced at Georgia State University to examine bulk samples of quarry spoils from the Plio-Pleistocene Nashua Formation of northern Florida.

This work focused on data from drilling predation and size-frequency distributions recorded in these marine molluscan assemblages. Three samples were sieved, sorted, and specimens identified to genus level if >5mm. Whole (>85% of the shell intact) and fragmented specimens were counted (only if the umbo or apex remained). Nearly 2,000 specimens have been processed, and ~70% of all samples were represented by whole specimens that could be used for studying size-frequency distributions and predator-prey interactions.

Taxa drilled in these samples included 9 bivalve and 4 gastropod genera. Complete and incomplete drillholes were documented. Mulinia dominated all samples, and only that genus (and collectively lucinids) had drillholes in all samples. Stereotypy data were additionally collected for Mulinia; results indicated that an overwhelming majority of drillholes were located in the umbo region. Analysis of size-frequency distributions revealed that bivalves mostly ranged between 5mm-20mm, whereas gastropods were distributed across a larger range of sizes. Taxa that are small are still being identified, so as sample processing is completed, results for predation will be compared to size-frequency distributions and examined in the context of other work in the region.