EXAMINATION OF ANTI-PREDATORY CHARACTERISTICS IN MOLLUSCAN FAUNAS FROM THE LOWER WACCAMAW FORMATION AT PRINCE’S QUARRY IN SOUTHEASTERN NORTH CAROLINA

Mollusks from the lower Waccamaw Formation at Prince’s Quarry were investigated for anti-predatory characteristics in defense of drilling by predatory gastropods as part of a paleontology class research project at Georgia State University. One large bulk sample was sieved using a ¼” mesh, and >1650 bivalves and gastropods picked, sorted, and identified to genus level. Only shells >5mm were analyzed including both fragmented and “whole” specimens (if ~85% of the shell was preserved). The “whole” specimens (~1200 bivalves, ~100 gastropods) were categorized into 5mm size bins and studied for signs of both successful and failed attempts at drilling predation.

To examine prey selectivity by gastropod predators, drilled genera were coded by the degree of surface ornamentation (1=smooth, 2=fine ribs, 3=coarse ribs, 4=spines). Drilling frequencies (=DF) were determined by category (if over 10 individuals were represented). Prey effectiveness (=PE) was calculated by category if at least 10 drillholes were documented. Size classes of both drilled and undrilled specimens in each genus were additionally compared to investigate size as a deterrent to drilling predation.

Of the 23 genera that were drilled, 90 complete drillholes and 11 incomplete drillholes were recorded. DFs decreased as ornamentation became more complex for bivalves (smooth=32%, fine=29%, coarse=16%, spines=14%). PE could only be calculated for bivalves exhibiting coarse ribs (12.5%) and fine ribs (9.3%). Limited gastropods precluded comparisons by ornamentation categories.

Size classes of bivalve genera subject to drilling ranged from 5mm up to 55mm, but no complete drillholes were recorded in shells >35mm. Size classes of gastropod genera subject to drilling ranged from 5mm up to 40mm, but no complete drillholes were recorded in shells >20mm. Incomplete drillholes were reported in larger size classes for select genera and in smaller size classes for genera restricted to small specimens. The results so far indicate that size refuges and shell ornamentation are effective defenses against drilling predation in faunas from the lower Waccamaw Formation at Prince’s Quarry. Future work will incorporate additional data from nearby localities as part of a broader study of regional changes in predator-prey relationships across the Plio-Pleistocene.