PREY SELECTIVITY BY THE PREDATORY DRILLING GASTROPODS: A MESO-CENOZOIC PERSPECTIVE

The earliest body fossils of predatory drilling gastropods – mainly the Naticidae and Muricidae – are known from the Cretaceous, although putative gastropod drill holes have been reported from the Triassic and Jurassic. This fossil record of drill holes has been used by several workers to study various aspects of the relationship between gastropod predators and their molluscan prey, but documentation of their dietary evolution through time is limited. Since the seminal work of Carriker and Yochelson (1968), it has been assumed that naticids mostly attack infaunal prey producing a beveled hole, whereas the muricids attack epifaunal prey producing a straight-walled hole. However, overlapping of diet certainly occurs, and drill-hole shape is not a reliable indicator of the predator (G. Herbert, pers. comm.). To test whether gastropod predators have displayed any preference for prey inhabiting particular habitat(s), we have compiled gastropod drill-hole data from the literature which also includes information related to bivalve prey habitats for four time intervals: the Triassic-Jurassic (phase of putative gastropod drilling); the Cretaceous (fossil evidence for the origin of naticids and muricids); and the Paleogene and Neogene (naticids and muricids diversified and became abundant). Our preliminary data show that their diet selectively included infaunal bivalve genera rather than epifaunal taxa (~75% of prey); this imbalance intensified during the Cenozoic (~90% drilled prey were infaunal). There are at least three potential explanations for these observations: 1) infaunal prey preference; 2) infaunal prey were more available, hence more frequently attacked; and/or 3) naticids have consistently been the dominant driller. Previous studies have documented that, apart from attacking the infaunal prey, naticids can also forage subaerially; while muricids mostly attack epifaunal taxa. These results suggest that the infaunal prey preference is not likely the case. A genus-level comparison of the habitats of all available bivalve for the studied intervals shows that although infaunal taxa are generally 20% more abundant than epifaunal ones, in terms of drilled taxa they comprise 75 to 90%. Therefore, naticids have been the dominant drillers, and they were attacking the more available infaunal bivalve prey.