Evolution of the Naticid Gastropod Predator-Prey System: An Evaluation of the Hypothesis of Escalation

Patricia H. Kelley
Thor Hansen, Western Washington University


Previous work has suggested that escalation may have characterized the history of the naticid gastropod predator-prey system, based on apparent increases in drilling frequencies and the occurrence of antipredatory aptations among prey. We evaluate this hypothesis based on a comprehensive survey (over 40,000 specimens) of predation on molluscs from the Upper Cretaceous through lower Oligocene formations within the U.S. Gulf and Atlantic Coastal Plain. Patterns in drilling of both bivalve and gastropod prey are complex. Drilling frequencies were relatively low in the Cretaceous but increased sharply above the Cretaceous-Tertiary boundary, remaining high until the late Eocene. Following a significant decline near the Eocene-Oligocene boundary, drilling frequencies increased to a moderate level in the Oligocene. Contrary to our prediction based on the hypothesis of escalation, no temporal trend of increasing stereotypy of drillhole site occurred. However, significant increases in prey effectiveness (indicated by the incidence of incomplete drillholes and multiply bored shells) occurred between the Cretaceous and Oligocene. This pattern characterizes entire faunas as well as individual prey taxa that were consistently heavily drilled (turritellid gastropods and corbulid bivalves).