The systematic status of Hanosaurus hupehensis (Reptilia, Sauropterygia) from the Triassic of China

Hanosaurus hupehensis was believed to represent a Middle Triassic thalattosaur from the People's Republic of China. Redescription of the holotype and only known specimen, and cladistic analysis of its interrelationships, shows Hanosaurus to represent a distinct pachypleurosaur. The two Chinese pachypleurosaurs, Keichousaurus and Hanosaurus, form two consecutive sister-groups to European pachypleurosaurs, strengthening the Asiatic affinities of the clade. Addition of Hanosaurus furthermore results in a modification of pachypleurosaur interrelationships as previously reconstructed: the pachypleurosaurs from the Germanic Triassic (Anarosaurus, Dactylosaurus) form a monophyletic clade, which is sister-group to the monophyletic clade of Alpine pachypleurosaurs (Serpianosaurus, Neusticosaurus). Thalattosauria are the sister-group of Sauropterygia, the two clades possibly representing a single invasion of the Mesozoic sea. However, more detailed knowledge of thalattosaur anatomy is required to further test the phylogenetic relationships of thalattosaurs.