Records of gastropod drilling predation on molluscan prey from the Anaipadi Member (Garudamangalam Formation; Upper Cretaceous, Coniacian) of the Ariyalur Sub-basin, India

Abstract

Predator-prey interaction constitutes important selection pressure in determining the evolutionary pathways for both involved parties. Here, we present a new dataset of gastropod drilling predation on molluscan prey from the Upper Cretaceous of the Ariyalur Sub-basin, India. While bulk sampling is the preferred protocol, this cannot be followed when the host rock is strongly lithified. A hybrid method of surface sampling, without physical breakage of the host rock, within a grid system is employed in the present study. The Coniacian Anaipadi Member (Garudamangalam Formation) yields a highly diverse fauna, including 25 species of bivalve and 16 species of gastropod. While the assemblage-level drilling intensity is 0.27 for bivalves, three common bivalve species exhibit drilling intensities ranging from 0.32 to 0.62. In the case of gastropods, a total of 27 complete drillholes have been found in four species, all belonging to the genus Turritella. As only a part of the shell was exposed, drilling intensities are not calculated for gastropods. Behavioural stereotypy of predators, in terms of prey size and drillhole location, is evident in some of the prey species, especially bivalves. A compilation of previously published literature data suggests that although drilling was an established mode of predation by the Late Cretaceous, the majority of this temporal bin is understudied. The present study provides the first report of drilling predation on molluscan prey from the Coniacian and provides the opportunity to expand our current understanding of drilling predation behaviour during the Late Cretaceous in a spatio-temporal context.