First record of varied archosauriforms from the Upper Triassic of India based on isolated teeth, and their biostratigraphic implications

ABSTRACT

A new rich and varied assemblage of archosauriform teeth is reported from the Upper Triassic Tiki Formation of India. Twelve morphotypes are identified based on their distinctive morphology, crown proportions, nature of serrations/denticles and serration density. Morphotypes I and II show similarity with that of Galtonia and Protecovasaurus, respectively, whereas morphotypes III–VI have low, subtriangular or leaf-shaped, asymmetrical, labiolingually compressed crowns with lenticular-subcircular bases and are diagnosed as belonging to different indeterminate archosauriforms. Morphotype VII shows similarity with aetosaur teeth, whereas morphotypes VIII–XII are ziphodont teeth having high, cylindrical, recurved crown with labiolingual compression, serrated carinae and subrectangular serrations, and are theropod-like. Variation in dental histology is noted between these morphotypes based on extent of pulp cavity, dentinal tubules and von Ebner lines of incremental growth. In multivariate analyses, there is considerable overlapping of convex hull polygons with morphospaces of other known archosauriforms such as Protecovasaurus, Crosbysaurus and Tecovasaurus known from the lower Tecovas Formation of the Chinle Group, USA. Such similarity correlates the two horizons despite wide geographic separation, suggesting that the age of the Tiki Formation may be younger than that previously suggested. Based on the known fossil flora and fauna, a mid-late Carnian age is proposed for the Tiki Formation.

KEYWORDS:

• Teeth
• archosauriform
• Tiki Formation
• Gondwana
• India

Acknowledgments

We are indebted to A. Bhaumik (Department of Applied Geology, Indian Institute of Technology (Indian School of Mines), Dhanbad, India), and M. A. Mamtani (Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India) for facilitating Scanning Electron Microscopy and automated polarising microscopy, respectively. N. Bhowmik, K. Datta, V. Rana and C. Desarkar are acknowledged for their assistance during thin section preparation and SEM. The constructive criticisms and comments of Gareth Dyke, Spencer G. Lucas and an anonymous reviewer are gratefully acknowledged. We thank SERB, DST, New Delhi (Project Ref. No: SERB/SR/S4/ES-604/2012) and the Indian Institute of Technology, Kharagpur, for providing financial support and necessary infrastructural facilities, respectively.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the Science and Engineering Research Board, Department of Science & Technology, New Delhi [SERB/SR/S4/ES-604/2012];