EXAMINING PREDATION IN MOLLUSCAN ASSEMBLAGES OF THE PLIO-PLEISTOCENE NASHUA FORMATION AT BUCK HAMMOCK MATERIALS IN DEER PARK, FLORIDA

Bulk samples were collected in September 2022 from the Plio-Pleistocene Nashua Formation at Buck Hammock Materials in Deer Park, Florida. Two samples (Upper 2A and Upper 3C) retrieved from the upper quarry wall were processed by paleontology students at Georgia State University in fall 2023. The bulk samples (~2 gallons each) were sieved and shells greater than 5 mm retained for analysis. Shells with umbos (bivalves) and apices (gastropods) were divided into whole (>85% of the shell intact) and fragmented specimens for paleoecological study including a particular focus on drilling predation. Most shells have been sorted, but identification of smaller taxa and fragmented individuals is still in process. Total genera reported so far are 12 for Upper 2A based on 2,844 whole shells and 228 fragmented shells and 24 for Upper 3C based on 3,401 whole shells and 511 fragmented shells. Whole shells were analyzed further for signs of drilling predation by documenting both complete and incomplete drill holes. Complete drill holes signify successful attacks, whereas incomplete drill holes indicate failed attempts at predation. Most drill holes were beveled and presumed to be made by naticid gastropods. Taxa commonly drilled in these samples included bivalves Anadara, Donax, and Mulinia. Data recorded from drill holes were then used to determine drilling frequency (DF) and prey effectiveness (PE). DF is calculated by dividing the number of complete drill holes by the total number of individuals. PE is calculated by dividing the number of incomplete drill holes by the total number of incomplete and complete drill holes. DFs varied but were consistently low in both samples whether analyzed by genus or by class (all <10%). PE was much more variable. Other bulk samples in process from the same location appear to show similar patterns. Further comparisons will be made in studying drilling predation up through the section at the quarry upon processing additional samples collected. Future work will also include a broader geographic study of changes in predation along the biogeographic boundary in north Florida to better understand extinction episodes of molluscan assemblages during the Plio-Pleistocene.