Abstract:

A bulk sample of a quartz-rich siltstone with a poorly preserved molluscan fauna was taken from the McBean Formation, approximately five miles north of Orangeburg, South Carolina, to look at the predator-prey relationships.  Fossils were preserved as molds, steinkerns, and casts.  Six hundred and six specimens were examined, including bivalves, gastropods, scaphopods and bryozoans, of which 139 were complete individuals identified either by a bivalve umbo or gastropod apex or encompassing more than half of the specimen.  Partials accounted for 467 specimens.  Two hundred and forty-six specimens (complete and partial) were sorted into 26 genera with bivalves dominated by Venericardia at 30% of the 246, Calorhadia at12% and the McBean Formation guide fossil Pteropsella lapidosa at 5%.  Gastropods were dominated by Eopleurotoma and turritellids, both at 4% of the total 246.  Thirty-seven individuals were identified to the species level with bivalves dominated by Leda bella (41%) and Pteropsella lapidosa at 30%. The gastropod Eopleurotoma lisboncola represented 5% of the 37 specimens and the only naticid, Natica semilunata, at 3%.  Only five specimens, all bivalves, had drill-holes.  Drilling frequency was calculated as 8%. This is a result that is closer to Gulf Coastal Plain drilling frequencies than to Atlantic Coastal states.  Prey drill-hole site selectivity was examined using a 9-sector grid for bivalve shells.  Three of the five drilled specimens had drill-holes located in sector two near the umbo, with the other two in sectors five and seven.  The one naticid gastropod predator found in this bulk sample was Natica semilunata.