A new typothoracine aetosaur (Archosauria, Pseudosuchia) from the Upper Triassic of India with insights on biostratigraphy, diversification, and paleobiogeography

ABSTRACT

A new typothoracine aetosaur is described based on multiple isolated and articulated left paramedian and lateral osteoderms recovered from the Upper Triassic lower Dharmaram Formation of India. The partial carapace of the new taxon is reconstructed as strongly discoidal based on the curvature of the paramedian osteoderms with the widest one positioned dorsal to the mid-dorsal trunk vertebra. Asymmetric lateral osteoderms with acute flexion are considered as precaudals with the angle of flexion decreasing posteriorly. Phylogenetic analysis recovered the new taxon as deeply nested within the clades Typothoracinae and Paratypothoracini, and a sister taxon to Kocurypelta silvestris. The autapomorphic characters involving paramedian osteoderms dorsal to the trunk vertebrae include dorsal surface ornamented by large, irregular pits surrounding the dorsal eminence and radiating ridges in other areas, straight anterior margin of the anteromedial corner of the anterior bar in dorsal view, and raised or ridged and ornamented posteromedial corner. The current study highlights the significance of the new aetosaur, and the age of the lower Dharamaram Formation is modified here as mid-Norian to Rhaetian based on global correlation with other coeval horizons. The recovery of this taxon marks the first record of Paratypothoracini from high paleolatitudes of the Gondwanan region. The study corroborates the earlier findings of a strong Laurasian faunal influx in India during the Late Triassic suggesting possible land bridges and/or conducive environmental conditions for faunal dispersal.

http://zoobank.org/urn:lsid:zoobank.org:pub:FCC37C0E-107F-4B15-9460-4E802B465865

ACKNOWLEDGMENTS

The fossil specimens were collected by T. S. Kutty, Geological Studies Unit, Indian Statistical Institute, Kolkata. We thank D. Mukherjee of the same Institute, and D. Datta, Department of Earth Sciences, Indian Institute of Technology, Roorkee for advice and help throughout the study. We thank A. Huttenlocker, T. Sulej, P. L. Godoy, and an anonymous reviewer for thorough revision and constructive suggestions. D. Pradhan and L. Mahankur are gratefully acknowledged for preparation and removal of matrices from the fossil specimens. The financial assistance was provided by Science and Engineering Research Board, India (SERB/CRG/000388) to SR. The Indian Institute of Technology Kharagpur and Indian Statistical Institute Kolkata are acknowledged for providing infrastructural facilities to AH and SR, and SB, respectively.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

AUTHOR CONTRIBUTIONS

SR, SB conceptualized and designed the project, AH, SR collected and analyzed data, AH drafted the manuscript, SR carried out interpretative line drawings, acquired funding and administered the project. All authors edited the manuscript.

SUPPLEMENTARY FILES

Supplementary File 1.docx: Details of the characters used for the phylogenetic analysis.

Supplementary File 2.nex: Combined characters and data matrix used for phylogenetic analysis.

Supplementary File 3.docx: Resampled MPTs (ordered).

Supplementary File 4.tre: MPTs of the parsimony analysis (unordered).

Supplementary File 5.docx: List of synapomorphies.