Effect of durophagy on drilling predation: a case study of Cenozoic molluscs from North America

Drilling predation represents one of the most widely studied biotic interactions preserved in the fossil record, and complete and incomplete drill holes have been commonly used to explore spatial and temporal patterns of this phenomenon. While such patterns are generally viewed solely in terms of the interactions between predator and prey, they might also be affected by extrinsic ecological factors. Recent experiments have demonstrated that in the presence of a secondary predator (crab), the incomplete drilling frequency increases indicating increasing abandonment of the prey, and drilling frequency decreases implying a decrease in successful attacks. Here, we tested whether the effect of secondary predators on drilling frequencies can be detected in the fossil record. Using fossil molluscs from six Plio-Pleistocene localities, we found that repair scar frequencies, a proxy for activity of durophagous predators, correlate directly with incomplete drill hole frequencies and inversely with complete drill hole frequencies. These results suggest that the activity and success of drilling predators is influenced not just by the prey, but also by secondary predators.