Middle Cretaceous (Cenomanian) bivalves from the Karai Formation, Uttattur Group, of the Cauvery Basin, south India

WA Museum Records and Supplements | Updated 7 years ago

ABSTRACT – Sixty species of Bivalvia, representing 28 families and 41 genera, are recorded from three outcrops of the Karai Formation (Uttattur Group, Cauvery Basin) near Odiyam village, Tiruchirapalli district, south India. Both Kunnam and Odiyam Members of the Formation are represented in the study material. An undifferentiated Cenomanian age is assigned to the fossil assemblages.

All species are described as fully as preservation and representation allow. Twenty three are redescribed with revised taxonomy. Newly described and named are the following 17 species: Nuculana (N.) odiyamensis, Nuculana (N.) arenicola, Grammatodon (Nanonavis) subcrenulatus, Trigonarca (Costelloiarca) punctulata, Atreta redunca, CallucinelIa marcida, CalIucinopsis? dalmiana, Paramyrtea (new genus) sabulosa, GoodalIia salebrosa, GoodalIia? australindica, Eriphyla (MiyakoelIa) badvei, Aenona? ariana, Aphrodina (A.) plebeia, Caryocorbula cauveriensis, Caestocorbula kubera, Lentidium (JanschinelIa) dissitum and Barcoona? gradilis. One new genus Paramyrtea - is erected. Lectotypes are designated for 18 species. Six families Noetiidae, Limopsidae, Propeamussiidae, Fimbriidae, Crassatellidae and Pholadomyidae - are recorded for the first time from the Uttattur Group.

Mollusca dominate the macro-assemblages. The bivalves constitute a diverse community of the transgressive, silty to sandy inner shelf, moderately energised and with good oceanic exchange at depths within the photic zone. Most of the genera are widely distributed in the Austral and Mediterran-Caucasian Realms of the Middle Cretaceous. Generic/subgeneric endemism is low, not exceeding 5%.