DECREASE THEN INCREASE IN PREDATION ON MICROBIVALVES BY JUVENILE NATICID GASTROPODS ACROSS THE PLIOCENE-PLEISTOCENE BOUNDARY, SOUTHEASTERN NORTH CAROLINA COASTAL PLAIN

The Pliocene-Pleistocene boundary in the Atlantic Coastal Plain of North America is characterized by two pulses of extinction in mollusks, including a decrease in predatory naticid gastropods that feed on clams and ostracodes by boring through the shell. Microbivalves and ostracodes were collected from three localities in southeastern North Carolina, one in the late Pliocene (3.0 Ma) Duplin Formation and two in the lower Pleistocene (2.2-1.5 Ma) Waccamaw Formation to determine predator-prey relationships of juvenile naticid gastropods associated with the boundary by the presence of bore holes on shells less than 2 mm in maximum dimension. More than 300 microbivalves assigned to 28 species and more than 300 ostracodes assigned to 20 species were recovered. The diversity of microbivalves increases above the Pliocene-Pleistocene boundary, the diversity of ostracodes decreases. The number of boreholes found in the clams indicates a decrease and then an increase in predation by naticid gastropods above the boundary in the upper Waccamaw: nine valves (5.4 %) were bored in Natural Well; 3.6 % (four valves) were bored at Register Quarry above the boundary in the lower Waccamaw; at Walker’s Bluff in the upper Waccamaw six valves were bored (5.8 %). One percent of ostracode valves were bored in the lower two localities, and two percent were bored at Walker’s Bluff. Juvenile naticids preferentially feed on juvenile bivalves and the rate of successful predation changes in the Pleistocene localities.

Additional authors: Jeffrey Over, SUNY-Geneseo and Gregory Dietl, Paleontological Research Institute, Ithaca, New York