Panzhousaurus rotundirostris Jiang et al., 2019 (Diapsida: Sauropterygia) and the recovery of the monophyly of Pachypleurosauridae

ABSTRACT

Panzhousaurus rotundirostris Jiang, Lin, Rieppel, Motani and Sun, 2019, is restudied on the basis of a second specimen from the Upper Member of the Guanling Formation near Panzhou City, Guizhou Province, China. The second specimen offers hitherto unknown or unconfirmed information regarding the dermal palate, the ventral aspect of the cervical vertebrae, and the hind limbs, thus permitting a refinement of the diagnosis. Newly added or modified diagnostic characters include paired frontals with no posterolateral process, elongated and slender phalanges in the manus and pes, and a phalangeal formula of 3-4-5-4-3 for the manus, and 2-3-4-5-3 for the pes. A new phylogenetic analysis of Eosauropterygia demonstrates that Pachypleurosauridae is the sister taxon of Eusauropterygia, and the monophyly of these groups as traditionally upheld is confirmed. Panzhousaurus is most closely related to Dianopachysaurus and Keichousaurus within Pachypleurosauridae. In this study, the monophyletic Pistosauroidea excludes Corosaurus and Cymatosaurus. The latter two genera are found to form a monophyletic clade that represents the basal-most members of Eusauropterygia, which is in accordance with their stratigraphic distribution.

ACKNOWLEDGMENTS

L. Schmitz, A. Boyd, S. Hinic-Frlog, and J.-Y. Shin joined the field trip and excavation in 2006 and helped with the collection of the specimen here described. We thank C. Li and Q.-H. Shang (IVPP), S.-X. Hu (CCCGS), L.-J. Zhao (ZMNH), C. Klug (PIMUZ), G. Teruzzi (MCSNM), T. Schossleitner (MNF-Berlin), E. Maxwell (SMNS), C. Ifrim (PGIMUH), J. M. Rabold (UMO-Bayreuth) and P. Vincent (MNHN) for providing access to the specimens under their care. W.-B. Lin especially thanks T. M. Scheyer for his help at PIMUZ. This research was supported by Projects 41920104001, 40920124002, and 41372016 from the National Natural Science Foundation of China, Grant 2016YFC0503301 from the Ministry of Science and Technology, Project 2020J05183 from the Natural Science Foundation of Fujian Province, Project 203112 from State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS), and Projects GY-Z18146 and GY-Z20091 from Fujian University of Technology. We also acknowledge the grant from the National Geographic Society Committee for Research and Exploration (#8669-09) to R. Motani. W.-B. Lin was supported by a grant from Peking University for three months of research in Switzerland.