Drilling predation and taphonomy in modern mollusk death assemblages, San Salvador Island, Bahamas

Studies of modern mollusk death assemblages provide an important framework for evaluating the fossil record. An analysis of 1951 shells from two beaches, Sandy Point and Haitian Boat Beach, on the isolated carbonate platform of San Salvador Island, Bahamas, has yielded significantly different frequencies of predation in bivalve-dominated assemblages. At Sandy Point Beach, bivalves and gastropods had a drilling frequency of 0.11 and 0.07, respectively. At Haitian Boat Beach, bivalves and gastropods showed a higher drilling frequency of 0.37 and 0.22, respectively. The prevalence of beveled drill holes suggests that the dominant predator was a naticid gastropod at both sites. Some ecological and environmental differences between the beaches could account for these disparate signals of predation: at Haitian Boat Beach, there is a higher abundance of the naticid Polinices sp. and it is a lower energy setting than Sandy Point Beach. Furthermore, radiocarbon dating of 17 shells at both beaches yielded a maximum age of > 6000 years before present, suggesting that these assemblages record a complex and long taphonomic history. These results imply that future large-scale coupling of predation studies with age dating of assemblages may provide important insights into the temporal structure of predation as well as the role of taphonomic loss of drilled shells.