ECOLOGICAL INTERACTIONS ACROSS A LATE PLIOCENE INTERVAL OF FAUNAL TURNOVER : NATICID CANNIBALISM NORTH AND SOUTH OF CAPE HATTERAS, NORTH CAROLINA

Previous work has indicated that over 70% of western Atlantic molluscan species became extinct during a pulsed event across the Plio-Pleistocene boundary; however, the fundamental nature of this extinction differs north and south of the biogeographic boundary represented by Cape Hatteras, NC. North of this boundary extinction without origination is thought to have occurred while south of the boundary, paleocommunities experienced both. Although the evolutionary effects of this extinction have been studied, the community-level ecological effects are poorly understood. This research focuses on confamilial ecological interactions among naticid snails, a family of shell-drilling predators, and seeks to determine the degree of cannibalism, changes in predator and confamilial prey size, and changes in naticid drill hole location across the biogeographic boundary during the late Pliocene.

This study compiled float and museum collections of the Yorktown (Moore House Member) and Duplin Formations (sampling before the extinction) and the lower Waccamaw and Chowan River Formations (sampling after the first pulse of extinction). Measurements included: percent cannibalism per collection (cannibalized naticids/total naticids), naticid size, prey size (drilled specimens), predator size (drill hole size), and drill hole location. Naticid size was calculated using geometric mean of length and height. Drill hole location was determined using an eight sector grid. To date, eight samples (4 pre-first pulse, 4 post-first pulse; 5 north of Cape Hatteras, 3 south of Cape Hatteras) have been processed totaling 447 specimens and representing nine species.

Preliminary results suggest a non-significant decrease in percent cannibalism and a non-significant increase in average size and maximum size across the first pulse of extinction. These results suggest that there was no difference in the confamilial ecological interactions of naticids across the first pulse of the Plio-Pleistocene extinction. Results were also non-significant when comparing naticids within 10mm size classes. This research is significant because it will lead to an understanding of how ecological interactions change across an extinction event and will define a baseline for naticid predator interactions across the Plio-Pleistocene boundary.