A review of small-bodied theropod dinosaurs from the Upper Cretaceous of India, with description of new cranial remains of a noasaurid (Theropoda: Abelisauria)

ABSTRACT

Small-bodied theropod dinosaurs are rare on southern landmasses but have been known from India for a century. Excavations by Charles Matley and Durgansankar Bhattacharji in uppermost Cretaceous sediments at Bara Simla, central India in 1917–1919 recovered small theropod vertebral and limb elements originally interpreted as coelurosaurians and separated into at least three species (Compsosuchus solus, Laevisuchus indicus, Jubbulpuria tenuis) based on features that can now be attributed to their serial position in the vertebral column. The comparatively recent discoveries of Noasaurus leali and Masiakasaurus knopfleri from similar-aged rocks in South America and Madagascar, respectively, and advances in basal theropod systematics led to a revised interpretation of most small-bodied Indian theropods as noasaurid abelisauroids. Here we review and redescribe Laevisuchus, Jubbulpuria, and Compsosuchus, including several elements that until now were thought lost, and describe a new partial noasaurid dentary from central India. The dentary bears the characteristic procumbent dentition of Masiakasaurus, which apparently is absent in Noasaurus. Likewise, cervical vertebrae of Laevisuchus more closely resemble those of Masiakasaurus than those of Noasaurus. Despite these similarities, phylogenetic analyses indicate that the balance of character data supports the Indian noasaurid species outside the sister-taxon pairing of South American and Malagasy species. Bones of small-bodied theropods have been recovered exclusively from the youngest Mesozoic localities in India (e.g., Pisdura, Bara Simla); to date they have not been reported from the slightly older localities in western and central India, from southern Indian sites in the Cauvery Basin, nor from the Vitakri Formation of Pakistan.

ACKNOWLEDGMENTS

This research was conducted under the auspices of a Memorandum of Understanding between RTM Nagpur University (BS) and University of Michigan (JAWM). For curatorial assistance, we thank Dr. A. Banerji, S. Sen, and S. Sengupta of the Curatorial Division of the Geological Survey of India, and D. Krause at SUNY Stony Brook. We thank K. Godham for field assistance. We are grateful to M. Carrano for discussions on noasaurids and for sharing then-unpublished data with us. We thank D. Pol and H. Zaher for information about the Spectrovenator matrix, which is available at MorphoBank. D. Pol provided assistance with the iterPCR script. R. Delcourt provided clarification for character codings associated with the axis of “Compsosuchus.” We thank M. Carrano and F. Novas for critical reviews of an earlier version of this manuscript, which greatly improved this paper. P. Godoy and H. Zaher provided assistance with TNT, which is freely available thanks to support from the Willi Hennig Society. We thank W. Sanders for the excellent preparation of the specimen and A. Dhobale for help with Figure 1. This study includes data produced in the CTEES facility at the University of Michigan, supported by the Department of Earth & Environmental Sciences and College of Literature, Science, and the Arts. The µCT scans were prepared by K. Rosenbach and processed by T. Abdul Kareem; full .tiff stack is available from the University of Michigan's Deep Blue Data at https://doi.org/10.7302/1f9q-9a65. DMM and BS are thankful to Head, Department of Geology, RTMNU, and Ministry of Earth Sciences Grant MoES/PO(GEOSCI)/49/2015 for facilitating the research. This research was conducted during visits to India supported by grants from the American Institute for Indian Studies, National Geographic Society (NGS 8127-06), and the National Science Foundation (NSF DEB 0640434, NSF EAR 1736606).

DISCLOSURE STATEMENT

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

AUTHOR CONTRIBUTIONS

DMM and JAWM designed the project. DMM and BS collected stratigraphic and sedimentological data portrayed in Figure 1. DMM, BS, and JAWM conducted paleontological reconnaissance. DMM and JAWM conducted collections research and photographed specimens. KVR and JAWM analyzed the phylogenetic data. JAWM drafted the manuscript, and all authors edited the manuscript. JAWM prepared all the figures.

SUPPLEMENTARY FILES

Supplementary File 1.pdf: Table S1, alveolar procumbency in dentary of the Pisdura noasaurid (RTMNU/DG/VERT/1/55P/2020) and Masiakasaurus knopfleri; Table S2, character states shared between Laevisuchus and other noasaurid taxa; and Figure S1, character distribution map of the Spectrovenator dataset (Zaher et al., 2020).

Supplementary File 2.nex: data matrix used in the phylogenetic analyses (NEXUS format). Characters and state descriptions are embedded.

Supplementary File 3.tre: most parsimonious trees generated from parsimony analysis.