NATICID DRILLING PREDATION ON GASTROPOD ASSEMBLAGE DURING THE LATEST MAASTRICHTIAN IN RAJAHMUNDRY, INDIA

One of the important forms of predatory interactions in the fossil record is drilling by predatory gastropods, namely naticids and muricids. Origination and diversification of naticids during the Cretaceous facilitates documentation of drilling frequency, as a proxy for overall predation intensity, on various molluscan taxa in the fossil record. Although drilling frequencies show fluctuating patterns, most of the previous studies suggest that naticid drilling predation was less intense during the Cretaceous and the modern values were already achieved after the K-T mass extinction, in the Paleocene.

Here, we tested this hypothesis with 31,929 gastropod specimens from the latest Maastrichtian Infratrappean bed in Rajahmundry, India. Our study suggests that assemblage-level naticid drilling frequency was significantly higher (~28%) than previously reported. Although relative abundance of different lineages varies within this assemblage, lineage-level drilling frequency also supports our finding of high drilling intensity in the Cretaceous. Naticid predators were highly efficient as it was evident from high DF (drilling frequency) and low PE (prey effectiveness) values as well as site and size stereotypy of the drillholes.

We conclude that naticid drilling-induced escalation was already established during the Cretaceous and the present find extends the paleobiogeography of naticid predation up to India. One potential explanation of higher drilling frequency in our Cretaceous samples is that while all other previous studies come from high latitude localities in U.S.A. and western Europe, Rajahmundry area belonged to the Northern sub-tropic during the Maastrichtian. Some of the previous studies indicated that naticid predation on modern taxa often shows a latitudinal gradient, i.e., increasing drilling frequency with decreasing latitude. Alternatively, our study may represent a local biogeographical hotspot of higher drilling intensity within a mosaic pattern of spatially heterogeneous naticid predation.