First rhynchocephalian (Reptilia, Lepidosauria) from the Cretaceous–Paleogene of India

ABSTRACT

Rhynchocephalia, a once diverse clade of lizard-like reptiles, had a nearly global distribution during much of the Mesozoic. By the Late Cretaceous rhynchocephalians underwent a marked reduction in their diversity and biogeographic range, with sparse records of only deeply nested taxa (e.g., Sphenodontinae) found in the Upper Cretaceous–Paleocene of Patagonia and the Miocene–Recent of New Zealand. Here we describe a partial dentary with teeth of a rhynchocephalian from the Naskal locality, an intertrappean deposit within the Deccan Traps Volcanic Province in peninsular India. This discovery represents the first Cretaceous–Paleogene (K–Pg) record of a rhynchocephalian outside of Patagonia and: (i) demonstrates the clade had a broader Gondwanan distribution during the Cretaceous than previously appreciated and (ii) reinforces the emerging pattern that Rhynchocephalia were confined to Gondwana after the Early Cretaceous. This further extends the rhynchocephalian record in India, which now spans most of the Mesozoic (Late Triassic to ca. K–Pg boundary). The Naskal rhynchocephalian is a member of Acrosphenodontia based on its regionalized, acrodont marginal dentition. Its hatchling teeth appear to be unique (e.g., crowns mesially tipped, distinct break in slope along distal margin) and most similar in morphology to those of Godavarisaurus lateefi from the Lower–Middle Jurassic of India. Although the Naskal intertrappean most likely was deposited during the latest Maastrichtian, additional fossil sampling across the K–Pg boundary in India is needed to determine whether the Naskal rhynchocephalian was a victim or survivor of the end-Cretaceous mass extinction.

ACKNOWLEDGMENTS

SA thanks GSI and Presidency College for providing access to fossil samples and laboratory research facilities. We thank S. Santana for access to the Santana Lab μCT scanner, B. Hovatter for μCT scanning, H. Fulghum for preliminary μCT data processing and 3D renderings, and M. Holland for reproduction of 3D print casts. We thank S. Evans for providing us with the high-resolution images of Rebbanosaurus jaini and Godavarisaurus lateefi for comparison. We thank M.E.H. Jones for comments on an earlier version of this manuscript. S. Evans and P. Romo de Vivar Martínez provided constructive reviews of this manuscript, and Associate Editor E. Maxwell and the technical editors provided useful suggestions. This research was supported by a grant from the National Science Foundation to co-PIs GPWM (EAR-1736787) and JAWM (EAR-1736606), grants from UCMP Welles Fund, the National Geographic Society, and the UW Royalty Research Fund to GPWM.