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.