Late Cretaceous gastropod drilling intensities; data from the Maastrichtian Fox Hills Formation, Western Interior Seaway, USA.

Drillholes interpreted as the products of gastropod predation have become the most widely applied proxy for predator-prey interactions in the fossil record. In a broader sense, they have also become accepted as reflecting the evolution of many aspects of predator-prey interactions; e.g., intensity, behavior, and efficiency. Because of the relative paucity of published studies, the generality of long-term trends revealed by recent compilations of drilling intensity data has not been widely tested. The present study examines predatory gastropod drilling intensity in bivalves from the late early to early late Maastrichtian Fox Hills Formation within the Western Interior Seaway (WIS). These data allow a new comparison to be made to drilling intensity values reported previously from coeval United States Coastal Plain collections. 6,910 valves and 4,343 articulated specimens representing 53 bivalve species were examined for evidence of drilling predation. Although the approach employed was designed to maximize the number of drillholes recorded, only 236 unequivocal drillholes, 20 possible drillholes, 11 partial drillholes, and a single specimen with multiple drillholes were found, resulting in a maximum drilling intensity of 3.3%. These drillholes are thought to have been largely produced by naticids, which are abundant in these deposits. When compared to other published studies of Maastrichtian gastropod drilling, these data document that drilling intensities in the latest Cretaceous varied considerably both spatially and temporally, and that the WIS record provides a lower baseline for Cretaceous drilling than that derived from coeval Coastal Plain localities.