Naticid drilling predation on gastropod assemblages across the K–T boundary in Rajahmundry, India: New evidence for escalation hypothesis

Abstract

One of the important and well documented prey–predator interactions in the fossil record is drilling predation done by naticid gastropods which diversified during the Cretaceous. Although drilling frequencies showed fluctuating patterns, most of the previous studies argued that naticid drilling predation was less intense during the Cretaceous and the modern values were achieved since the Paleocene.We, here, present a new dataset of naticid drilling predations, involving 31,929 gastropod specimens, from the latest Maastrichtian Infratrappean bed in Rajahmundry, southern India. These specimens belonged to 40 species of 20 families, thus representing a spectacular gastropod diversity that was not known until recently from this region. We examined 5884 complete or near complete specimens to quantify naticid drilling predation on this assemblage. It appeared that drilling frequency was significantly higher from all previous Cretaceous values. This was true for both assemblage-level and lower taxon-level results. Along with high successful drilling and low unsuccessful drilling frequencies, site and size stereotypy of drillholes suggest that naticid predators were highly efficient, even in the Cretaceous. Predators were prey selective and there was poor correlation between relative abundance and drilling frequency of prey taxa.The present Maastrichtian assemblage underlies the K–T mass extinction level. Drilling frequency was zero in the straddler prey community in the Intertrappean bed found immediately above the K–T boundary. The absence of any drillhole in surviving prey taxa may be due to sudden reduction in abundance of escalated predators, although some prey taxa e.g., cerithiids continued. This emphasizes the role of mass extinction in disrupting predator–prey interaction.We conclude that naticid drilling-induced escalation was already established during the Cretaceous and the present find extends the paleobiogeography of naticid predation (which was previously reported from the western world) up to India.