关键词: 云南罗平, 中三叠世安尼期, 始鳍龙类, 幻龙属

Abstract:

Nothosaurus luopingensis sp. nov. from Member II of the Guanling Formation (Anisian, Middle Triassic) of Luoping, Yunnan, China is described based on a specimen comprising the skull and most of the postcranial skeleton. The specimen is assigned to Nothosaurus of Eosauropterygia as suggested by a series of skull characters, such as the maxillary tooth row extending posteriorly beyond the level of the anterior margin of the upper temporal fenestra, the longitudinal diameter of the upper temporal fenestra more than twice as long as that of the orbit, and the presence of maxillary fangs. Compared with Lariosaurus, the following morphological features of the pectoral girdle and the limbs also support the assignment of the specimen to Nothosaurus, i.e., the clavicles with expanded anterolateral corners, the characteristically curved humerus with a straight preaxial angle and a postaxial concavity, the distinct deltopectoral crest on the proximal part of the humerus, no hyperphalangy in the manus, and the absence of pachyostosis in the vertebrae and ribs. On the other hand, the specimen possesses some postcranial features that were previously considered to occur mainly in Lariosaurus, such as more than three ossifications in the carpus, four sacral ribs, and an interclavicle without any trace of a posterior stem. These postcranial characters may no longer be used as the diagnostic features of Lariosaurus. Nothosaurus luopingensis is distinguished from other Nothosaurus species by a unique combination of derived characters, including that the jugal enters the orbit, the nasals are separated, the posterior end of the frontal is bifurcate, pedal digits V and IV are long and subequal in length, and the ungula phalanx is stout. Our phylogenetic analysis corroborates the monophyly of Nothosaurus and suggest that N. luopingensis is the sister group of N. yangjuanensis.

Key words: Luoping, Yunnan, China, Middle Triassic, Anisian, eosauropterygian, Nothosaurus