A new pachypleurosaur (Reptilia: Sauropterygia) from the lower Middle Triassic of southwestern China and the phylogenetic relationships of Chinese pachypleurosaurs

ABSTRACT

A new genus and species of Pachypleurosauria, Dianopachysaurus dingi, gen. et sp. nov., from a recently discovered Middle Triassic Lagerstätte in the Anisian Guanling Formation of Yunnan Province is described. The monophyly of Pachypleurosauria, including all potential Chinese pachypleurosaurs in this study, is supported by the rigorous cladistic analysis conducted here. Phylogenetic relationships of Chinese pachypleurosaurs are clarified. Wumengosaurus occupies the most basal position within Pachypleurosauria. Keichousaurus and Dianopachysaurus form the monophyletic Keichousauridae that is the sister group of all European pachypleurosaurs. Our cladistic analysis also supports a previously proposed paleobiogeographic hypothesis of an eastern Tethyan origin of pachypleurosaurs and their migration into the western Tethyan faunal province. The existence of a long ghost lineage as required by the paleobiogeographic hypothesis is greatly shortened by the discovery of Dianopachysaurus.

ACKNOWLEDGMENTS

We thank S. X. Hu, T. Lv, and J. K. Bai from CCCGS for their help in the field, F. R. O’Keefe for editorial assistance and helpful suggestions, and J. Müller and an anonymous reviewer for constructive reviews. J.L. especially thanks M. F. Zhou (The University of Hong Kong) for his help that made this study in Chengdu possible and J. Z. Xue (Peking University) for his reading of the manuscript and helpful suggestions. J.L. is supported by a postgraduate studentship by The University of Hong Kong. D.Y.J. was supported by the National Natural Science Foundation of China (Project No. 40920124002) and the Program for New Century Excellent Talents in University (NCET-07-0015). This is a contribution to Project No. 1212010610211 funded by China Geological Survey.

Handling editor: Robin O'Keefe.