Evidence of biotic interactions through shell repair on Early Cretaceous gastropods from west-central Argentina

Abstract

Evidence of durophagous predatory behavior on benthic invertebrates in the Upper JurassiceLower Cretaceous of the Neuquen Basin is scarce, despite the abundant record of potential predators. Herein, we document shell repair in one gastropod from lower Barremian marginal-marine deposits in northern Neuquen Basin, Argentina. This is the first report of shell repair on Early Cretaceous gastropods from Argentina and of shell repair frequencies from the Lower Cretaceous. Paleoanculosa macrochilinoides shells from three sections of the La Tosca Member (Huitrín Formation) in Mendoza province were studied. We described and interpreted the repaired breakage, calculated repair frequencies which were compared among localities, tested for geographic differences in size distribution of total samples and of repaired vs. undamaged shells, and assessed whether this species reached a size refuge. Studied shell repair consists of fractures cutting through growth lines roughly diagonally, from suture to suture, and near the aperture, thus representing apertural damage. Given its stereotypical nature, the damage represents the record of a biotic interaction, likely sublethal predation, instead of diagenetic compaction or damage by physical disturbance. Repair frequencies are low, indicating that shell architecture made P. macrochilinoides susceptible to lethal predatory attacks, or else that there were few predator-prey encounters. There are no major geographic differences regarding repair frequency, size distribution, and preservation. Likely, P. macrochilinoides did not reach a size refuge. This study provides evidence from both a time slice and geographic area with scarce data on crushing predation and from an inbetween phase within the Mesozoic Marine Revolution.