PALEOECOLOGY OF THE WACCAMAW FORMATION (PLIO-PLEISTOCENE) OF NORTH CAROLINA: AN ACTUALISTIC APPROACH

An actualistic approach was used to study molluscan assemblages of the Waccamaw Formation (Plio-Pleistocene) collected from Old Dock, Columbus County, North Carolina, as part of an undergraduate invertebrate paleontology course at University of North Carolina at Wilmington. Teams of students collected and wet sieved bulk samples of the Waccamaw Formation, picked all whole pelecypod valves and gastropod shells, and identified them to species level (~200 individuals per sample). Data were tabulated on diversity and ecological relationships, particularly drilling by predatory naticid gastropods. Each student also applied the same techniques to analyze a sample collected from a modern beach for comparison with the Waccamaw samples. Twelve modern beach samples were used, collected from Maine, Massachusetts, New Jersey, Delaware, North Carolina, Georgia, and Florida. The Recent samples varied in frequency of naticid drilling from 0 – 4% in Maine and Massachusetts to 18 – 26% in the middle Atlantic states to a maximum of 35% in Florida for the entire molluscan assemblage. A similar pattern of declining drilling frequencies with latitude occurred for the gastropod fauna, bivalve fauna, and infaunal bivalves. Arcid bivalves, which were not present at the most northerly localities, usually exhibited drilling frequencies somewhat greater than that of the fauna as a whole. Drilling frequencies in the Waccamaw varied among samples from 24% to 30% for the entire fauna; bivalves and gastropods were drilled roughly equivalently and, as in the modern samples, arcids were drilled at a greater frequency than were bivalves as a whole. Waccamaw drilling frequencies were consistent with those of modern samples from Delaware south to Stuart Beach, Florida, although the more tropical aspect of the Waccamaw fauna suggests an environment similar to that near the southern end of the range. Waccamaw drilling frequencies in this study were greater than those reported in previous studies of the fauna (~12%), perhaps because a larger mesh size (1/4 inch rather than 1 mm) was used in sieving the samples in order to allow completion of the project within the context of an undergraduate course.