A long-due taxonomic re-evaluation of the Late Cretaceous (Coniacian-Santonian) brachiopods of Ariyalur, India, and their implications.

The present study provides a long-due taxonomic evaluation of the brachiopods of the Ariyalur sub-basin, Cauvery Basin, India. After the seminal works of Stoliczka (1872), this is the first study on the Late Cretaceous Trichinopoly Group brachiopods. 1507 specimens were collected from the medium-sized sandstone units of the Anaipadi Member and Kulakkanattam Member of the Garudamangalam Formation. Based on their morphology, six rhynchonellid and two terebratulid species are identified. The terebratulids, Sahnithyris andurensis, and Carneithyris carnea are distinctly differentiated based on their body size, shape, and plication. The rhynchonellids,  Sillakkudirhynchia plicatiloides, Protegulorhynchia cranifera, Tegulorhynchia squamosa, Orbirhynchia nutans, Orbirhynchia multicostata, Orbirhynchia arrialoorensis are mainly distinguished by the ornamentation pattern, pedicle opening, convexity of both valves and sulcus patterns . Small rhynchonellids dominate our collected samples, and bigger terebratulids represent only 3% of the brachiopod assemblage. Among rhynchonellids, Sillakkudirhynchia plicatiloides, Protegulorhynchia cranifera, Tegulorhynchia squamosa are dominant species. Sillakkudirhynchia plicatiloides shows a right-skewed, Protegulorhynchia cranifera shows a left-skewed, Tegulorhynchia squamosa shows a bell-shaped size distribution due to their difference in mortality rate, recruitment. This study reports the first brachiopod drilling predation from Coniacian.   A drilling frequency of 4.3% was observed with predators showing valve selectivity, taxon selectivity, and size (8-17mm) selectivity of prey. A biogeographic study is carried out with the help of six genera and thirteen locations incorporated into four biogeographic regions. India shows its closest similarity (Jaccard = 0.84, Dice = 0.90) with Antarctica and its association with the Austral region. Based on the brachiopod genera distribution, cluster analysis depicts the Austral region’s biogeographic connections with the Central European Region. This indicates probable active seaways through Eastern Tethys to the South Atlantic Ocean during the Late Cretaceous.