INTENSITY OF DRILLING PREDATION ON SEAFOOD THROUGH TIME: ASSEMBLAGE VS TAXON ESTIMATES

Predation by drilling gastropods provides evidence of predator-prey interactions rarely available in the fossil record for other systems; the record of gastropod drilling has been used to test hypotheses concerning the role of ecology in evolution. Initial tests of the hypothesis of escalation employed assemblage-level estimates of drilling frequencies. Use of assemblage-level data to estimate predation intensities has been criticized because results based on such data may be confounded by varying relative abundances of prey taxa with different morphologies and adaptive syndromes. Our database on naticid gastropod drilling includes 150,000 bivalve and gastropod specimens from 28 Atlantic and Gulf Coastal Plain formations (Cretaceous through Pleistocene). We extracted data for eight common bivalve and gastropod prey families for comparison with assemblage-level estimates of drilling to test the robustness of temporal patterns previously derived from these assemblages. Despite changing relative abundances of taxa through time, the general patterns of temporal change in drilling apparent at the assemblage level also occur within taxa. At the assemblage level, drilling frequencies were relatively low in the Cretaceous, declined across the K-T boundary, rose dramatically in the early Paleocene, remained high until a late Eocene decline, and then rose significantly after the Eocene-Oligocene mass extinction. This general pattern of drilling is replicated at the family level, especially for the Turritellidae, Corbulidae, and Lucinidae, which are consistently present in Cretaceous through Oligocene assemblages. Taxa more sporadically abundant (Arcidae, Noetiidae, Carditidae, Crassatellacea) when present also exhibit the decline in drilling across the K-T boundary, high drilling frequencies in the Paleocene through middle Eocene, lower late Eocene drilling frequencies, and higher frequencies in the Oligocene. Drilling predation on naticid gastropods shows greater departure from the assemblage-level trends, perhaps due to the complex nature of naticid predation on naticids. Use of assemblage-level estimates in concert with analyses of lower taxa enables reconstruction of the history of predator-prey interactions and testing of hypotheses concerning the role of ecology in evolution.