BRIDGING A BIOGEOGRAPHIC GAP BY STUDYING PLIO-PLEISTOCENE EXTINCTION EPISODES THROUGH MOLLUSCAN ASSEMBLAGES OF GEORGIA AND NORTHERN FLORIDA

Extinction episodes of molluscan faunas across the Plio-Pleistocene have been studied for numerous marine units exposed in the southeastern U.S. and in the Caribbean. Timing and causal mechanisms impacting extinction events are reported to vary biogeographically. Work on fossil deposits from the Atlantic Coastal Plain in the southeastern U.S. has focused primarily on well-known stratigraphic units in southern Florida (e.g., Caloosahatchee) and in the Carolinas (e.g., Duplin, Waccamaw). The fossil-rich Nashua Formation from the Plio-Pleistocene of northern Florida, however, has received less attention. Similarly, molluscan faunas in Georgia have not been analyzed in the context of Plio-Pleistocene extinction episodes, primarily due to limited exposures relative to other units in the region. The goals of this study are to bridge a biogeographic gap by building knowledge of assemblages that border the boundary between the Carolinian and Gulf molluscan faunal provinces by compiling data for fossiliferous deposits from Georgia and northern Florida.

Plio-Pleistocene fossils from Georgia were studied primarily from museum collections from various institutions in the region (e.g., Fernbank Science Center, Georgia Southern University, Florida Museum of Natural History). Ongoing data-mining and study of borrowed collections has yielded a new database of Plio-Pleistocene fossils for over 12,500 specimens recorded from Georgia. Top genera for bivalves include Mulinia, Donax, Anadara, Pleuromeris, Abra, Mercenaria, and Ervilia. Top genera for gastropods include Neverita, Crepidula, Terebra, Oliva, Natica, Nassarius, Busycon, Anachis, and Acteocina.

Specimens analyzed from the Plio-Pleistocene Nashua Formation of northern Florida include bulk samples of quarry spoils collected in September 2018. Three locations at a quarry were sampled and specimens sieved, sorted, and identified by students in a paleontology class at Georgia State University. Data collection is still in process, but so far, nearly 2,000 specimens have been studied. To date, 47 bivalve and 26 gastropod genera have been identified. Samples are dominated by Mulinia for bivalves; gastropods are well-represented by Oliva, Conus, and Crepidula. Future work will analyze these results in the context of extinction patterns in the region.