A new Bartonian elasmobranch assemblage from the Kutch Basin, western India, and its significance in the context of paleoclimate change

ABSTRACT

The upper part of the Harudi Formation of the Kutch basin in Gujarat, western India, has recently yielded a heretofore undocumented assemblage of elasmobranchs, including extinct sand tiger sharks Brachycarcharias lerichei and Striatolamia macrota, extinct tiger sharks Galeocerdo eaglesomei and G. clarkensis, requiem shark Carcharhinus mancinae, as well as sawfish Pristis sp. A bony fish taxon represented by Trichiurus sp. was also recovered. After a 43-years gap, this study provides a taxonomic update on the middle Eocene sharks of Kutch. Their coexistence with the larger benthic foraminifera Nummulites obtusus and planktonic foraminifera Orbulinoides beckmanni dates this fish fauna to 40–41.03 Ma, which corresponds to the time frame of the Bartonian transgression and extreme warming event Middle Eocene Climatic Optimum (MECO). The MECO elasmobranch assemblage of Kutch comes from shelf settings with bathymetry of 30–60 m, and it differs from those associated with Paleocene–Eocene hyperthermal events and deposited in the bay complex. It seems that G. clarkensis and C. mancinae emerged in Kutch during MECO. The global stratigraphic distribution demonstrates that B. lerichei and S. macrota originated in North America, and their appearance in Kutch expands their geographic range into the eastern Tethys realm, possibly as a result of MECO-linked Bartonian/Kirther transgression.

KEYWORDS:

• Elasmobranchs
• middle eocene
• MECO
• India
• palaeobiogeography
• climate change

Acknowledgments

The author is grateful to Dr. Gareth J. Dyke, the editor, for giving him an opportunity to revise the manuscript. Many thanks to two anonymous reviewers for their constructive comments and insightful recommendations, as well as meticulous linguistic refinements. Dr. Giuseppe Marramà is gratefully acknowledged for clearing up a few doubts about the Brachycarcharias lerichei. The author is thankful to the NMH-IV and Dy. DG MIV-C, Geological Survey of India (GSI) for allowing him to carry out this research and providing necessary laboratory facilities and administrative support. The author sincerely acknowledges Dr. Debahuti Mukherjee, Director Palaeontology Division, CHQ, for her useful suggestions and some grammatical corrections. The author would like to thank Dr. Arindam Roy and Dr. Danish Anwar for their help and technical suggestions over the course of this article. Many thanks to Pummy Roy for being helpful with preparing the litholog of the HT section. The author acknowledges the facility extended to him for microscopy of fossils at Palaeontology Division, ER GSI, Kolkata. The author expresses profound gratitude to countless senior and subordinate officers of the Geological Survey of India for their consistent encouragement and motivation. The study was carried out as part of the research project (FSP no. M4RP/NC/CHQ/2020/36475), Palaeontology Division, Central Headquarters, Geological Survey of India. This research paper is dedicated to Prof. Sunil Bajpai for introducing the author to the fascinating world of Vertebrate Palaeontology. Finally, I want to thank my amazing wife Shweta for her support, without which I would not have been able to complete this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).