Abstract: An almost complete Nothosaurus specimen is described in particular from the Upper Member of the Guanling Formation (Pelsonian, middle Anisian, Middle Triassic) of the Xinmin District, Panxian County, Guizhou Province, Southwestern China. The specimen provides new information on the postcranial osteology of the species. The diagnosed features of the species are revised by the following characters: four premaxillary fangs followed by one small conical premaxillary tooth and five to six small maxillary conical teeth followed by paired maxillary fangs, no posterior process in the interclavicle, four carpals, four sacral vertebrae and hyperphalangy in both manus and pes. In some aspects of its postcranial morphology, GMPKU-P-3014 appears to approach Lariosaurus more closely than Nothosaurus, such as no posterior process in the interclavicle, four carpals, four sacral vertebrae and hyperphalangy in both manus and pes, which provides the important characters to reevaluate the phylogenetic relationships of Nothosaurus and Lariosaurus within the Sauropterygia. GMPKU-P-3014, GMPKU-P-1080 and IVPP V 14294 are different from all other nominal species of Nothosaurus by their size, dentition and the skull future pattern. In addition they have the most similar shape and important proportions of the skull, as well as the same location and stratigraphic level. Thus, they are the same species and indicates that N. rostellatus is a junior synonym of N. yangjuanensis and should be abandoned.

Key words: Nothosaurus yangjuanensis, Nothosaurus, Middle Triassic, Panxian County, Guizhou Province

摘要： 详细描述产自贵州省盘县新民乡羊圈村中三叠统关岭组上段的一件近于完整的羊圈幻龙新标本, 并补充完善该种头后骨骼学信息。厘定后的羊圈幻龙的鉴定特征为: 4个前颌骨獠齿后面跟着一个小的前颌骨齿; 5~6个小的上颌骨齿后面跟着一对上颌骨獠齿; 腕骨4块; 间锁骨没有后突; 荐椎4块; 存在多指(趾)式。新标本的头后骨骼首次呈现一些原认为仅出现在幻龙属姊妹群??鸥龙属的一些特征, 如间锁骨没有后突, 腕骨 4块, 荐椎4块及存在多指(趾)式。 这些特征的发现为深入认识和区分幻龙属和鸥龙属之间性状的异同提供了重要的信息。另外, 新标本与羊圈幻龙模式标本, 以及相同地点、相同地层层位产出的小吻幻龙模式标本 IVPP V 14294在体型、齿式和头骨骨骼模式等高度一致, 且与幻龙属其他种明显不同, 因此认为它们系同物异名。鉴于N. rostellatus后出, 应予弃用。

关键词: 羊圈幻龙, 幻龙, 中三叠世, 盘县, 贵州