INOCERAMIDS FROM THE MAASTRICHTIAN KALLANKURICHCHI FORMATION, ARIYALUR, INDIA

Inoceramids are one of the most diverse and abundant components of the bivalve ecosystem in the Late Cretaceous. Ariyalur Sub-basin of the Cauvery Basin in India has been documented to preserve an exceptionally rich record of bivalve fossils of the Late Cretaceous. Although inoceramids of the Ariyalur strata have been known for more than a century, a review of taxonomic classification is long warranted. The present study aims to document the diversity of inoceramid bivalves from the Maastrichtian Kallankurichchi Formation of the Ariyalur Sub-basin. Based on nine different morphological parameter measurements from the external view, preliminary results suggest the presence of seven species of inoceramids – Inoceramus borilensis, Inoceramus sagensis, Inoceramus convexus, Inoceramus redbirdensis, Cataceramus mortoni, Cataceramus balticus, and Cataceramus glendivensis – from three lithostratigraphic members of the Kallankurichchi Formation. When compared with other recent studies, it appears that the diversity of inoceramid bivalves did not change significantly from the Upper Albian – Lower Turonian Karai Formation to the Maastrichtian Kallankurichchi Formation. However, there are significant changes in morphology. Inoceramids are significantly larger in the Kallankurichchi Formation, and the overall shape has also been shifted from subtriangular to rounded or sub-rectangular. While few studies from other parts of the world documented the predation traces on inoceramid bivalves, there was no previous record of predation on inoceramids from India. Nearly 10% of the specimens from the Kallankurichchi Formation exhibit traces of durophagous predation. These records suggest that the inoceramids were a part of the durophagous predators’ diet in the Late Cretaceous throughout the world. This study offers important insights into inoceramid diversity, morphological evolution, and predator-prey interactions, facilitating a deeper understanding of the overall community structure of the Ariyalur sub-basin during the Maastrichtian.