TAXONOMIC AND ECOLOGICAL DIVERSITY OF MOLLUSCAN ASSEMBLAGES FROM THE PLIO-PLEISTOCENE NASHUA FORMATION OF NORTHERN FLORIDA

Bulk samples of quarry spoils from the Plio-Pleistocene Nashua Formation of northern Florida were analyzed as part of a research project in a paleontology class at Georgia State University. Three samples were collected from different locations in the quarry and sieved for specimen study and paleoecological analyses. Other stratigraphic units in the region that straddle the Plio-Pleistocene have been more commonly studied; however, extinction episodes across this boundary are reported to vary geographically with regard to the faunas impacted and causal mechanisms. Thus, it is important to build an understanding of under-studied fossiliferous deposits that represent an existing biogeographic gap in knowledge.

Nearly 2,000 specimens have been processed. Data collection is ongoing, but so far, at least 47 bivalve and 26 gastropod genera have been identified. All samples are dominated by Mulinia ranging from 38% up to 57% of individuals across samples. Other common bivalves include several genera of arcids and lucinids. Gastropods make up 10%-25% of individuals in these samples. Well-represented genera across all samples are Conus, Oliva, and Crepidula. Other genera such as Olivella, Prunum, and Terebra are common in a few but not all samples. Taxa that are rare have yet to be fully identified. Preliminary results using rarefaction as well as diversity and evenness measures have been analyzed in making comparisons across all samples; data will be re-evaluated once sample processing has been completed.

Life modes of genera were additionally investigated using the NMITA database for classification of feeding habits for gastropods and bivalves. Attachment, mobility, and relationship to the substrate were also recorded for bivalves. To date, data on bivalves indicate that 67% of all genera and 88% of all individuals are suspension feeders. Most bivalve genera are actively mobile, infaunal, and unattached. Gastropods are represented primarily by predatory carnivores. Future work will continue to examine patterns of diversity at both the genus level and ecologically as well as add comparisons to other correlative fossiliferous units in the region.