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

摘要：

根据产自云南罗平中三叠统关岭组II段的一件海生爬行动物骨架,建立和描述了始鳍龙类幻龙科幻龙属的一个新种——罗平幻龙(Nothosaurus luopingensis sp. nov.)。该骨架包括完整的与上下颌紧密咬合的头骨和不太完整的头后骨骼,头后部分包括全部的颈椎、大部分背椎,前两个尾椎以及大部分的肩带、腰带骨骼以及四肢骨骼。新标本具有长而扁的头骨,颞孔较大,顶孔相对靠后,上颌骨发育獠齿型齿,上枕骨封闭并呈水平展布,这些特征指示该骨架属于鳍龙类的幻龙类。而头骨上颌齿列的后伸超过上颞孔前缘的水平位置,上颞孔的长度是眼眶长的两倍多等特征指示它具有更多的幻龙属(Nothosaurus)近裔共性。与欧龙属(Lariosaurus)相对比,新标本的肩带和四肢结构也具有幻龙属特征,如：锁骨前外侧角显著扩张,弯曲的肱骨前缘具有平直的轴前角,肱骨有明显的三角胸嵴,手部不具有多指节现象,脊椎无肿骨现象等。另一方面,该骨架的头后骨骼也显示一些之前曾主要发现于欧龙属的头后骨骼特征,如：骨化的腕骨数目超过3枚,具四节或更多的荐椎,间锁骨后缘平直、不发育后突。这些头后骨骼特征已经不能再用来区别欧龙属和幻龙属。罗平幻龙以下面这些衍生特征与其他幻龙属种区别,包括：轭骨前部进入眼眶,两鼻骨分离,额骨后端分叉,第IV、V趾长且长度相等,爪趾骨显著膨大。系统发育分析支持新种属于Nothosaurus, 它和羊圈幻龙(N. yangjuanensis)互为姊妹群,同时Nothosaurus是单系类群。

关键词: 云南罗平, 中三叠世安尼期, 始鳍龙类, 幻龙属