A new tanystropheid (Diapsida: Archosauromorpha) from the Middle Triassic of SW China and the biogeographical origin of Tanystropheidae.

Tanystropheidae is a clade of early archosauromorphs with high morphological disparity and a wide geographical distribution. The origin and early radiation of Tanystropheidae are still incompletely understood. Here we report Luxisaurus terrestris gen. et sp. nov., a new archosauromorph collected from the marine Upper Member of Guanling Formation (Pelsonian substage, Anisian, Middle Triassic) in Luxi County, Yunnan Province, China, and phylogenetically recovered as a tanystropheid. The morphology of Luxisaurus is consistent with a terrestrial lifestyle. This is the first occurrence of a tanystropheid found from the Anisian Guanling Formation in SW China and also the earliest tanystropheid from the eastern Tethys. Phylogenetic analysis shows that Dinocephalosauridae forms the sister group of Tanystropheidae, Fuyuansaurus occupies the most basal position in Tanystropheidae, and Luxisaurus forms the sister group to a clade consisting of all other tanystropheids. Considering that Fuyuansaurus and Luxisaurus are found exclusively in South China, we hypothesize that Tanystropheidae originated in the Early Triassic of South China and then dispersed globally. The discovery of Early Triassic tanystropheids in South China is needed to further support this hypothesis. The discovery of Luxisaurus expands the stratigraphical and geographical distribution of Tanystropheidae, and provides new insights into the origin and early radiation of the clade. [ABSTRACT FROM AUTHOR]