Pre-burial taphonomic imprints on drilling intensity: a case study from the recent molluscs of Chandipur, India

ABSTRACT

Palaeoecological studies of drilling intensity (DI), drawing ecological and evolutionary inferences, generally assume that drilled and undrilled specimens are equally preserved in the fossil record, because of the fact that the presence of drillholes does not affect preservation potential during sediment compaction. However, another facet that has not been studied conclusively is the taphonomic imprint on DI in a pre-burial scenario. If drillholes add weakness to a shell’s mechanical strength, drilled valves may preferentially be broken during post-mortem transportation, before its’ burial within sediment. In the present study, we test this hypothesis with a dataset involving DI and taphonomic status of two bivalve, Donax scortum and Mactra luzonica and two gastropod, Natica tigrina and Turricula javana species from Chandipur, India. Taphonomic status of each specimen is determined by relative preservation of its’ morphological characters. In case of both bivalves and gastropods, DI is found to be highest among the best preserved specimen and, thereafter, declines with increasing taphonomic degradation. When shell size is included in analyses, DI still shows an inverse relation with taphonomic alteration. This observed inverse relationship between drilling intensity and taphonomic imprint suggest that drilled shells may be vulnerable to breakage by pre-burial taphonomic processes.

KEYWORDS:

• Drilling intensity
• biostratinomy
• taphonomy
• naticid predation

Acknowledgments

SP thanks INSPIRE Faculty Research Program, funded Department of Science and Technology (DST). SM acknowledges Department of Science and Technology (DST)–Science and Engineering Research Board (SERB) Fast Track Award (SR/FTP/ES-133/2014) and Department of Geology, University of Calcutta Research Grant (RGT, 2018) for partial funding. We thank S. Bardhan and S.S. Das for their valuable suggestions on several aspects of this work. We thank A. Das for his help in initial data collection. This manuscript was improved by thoughtful reviews from PH Kelley and two other anonymous reviewers.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Department of Science and Technology, Ministry of Science and Technology [INSPIRE Faculty Research Grant]; Science and Engineering Research Board [SR/FTP/ES-133/ 2014].