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| Austronaga minuta Wang, Lei & Li, 2024 |
Abstract
Among numerous marine reptiles discovered in the Triassic eastern Tethys, today’s Southern China, Dinocephalosaurus is a bizarre animal comparable to European Tanystropheus in developing a prominently long neck. These two taxa are respectively assigned to Dinocephalosauridae and Tanystropheidae, and the two families and other basal members collectively form an early-diverging clade of Archosauromorpha. Here we report a new archosauromorph specimen, IVPP V18579, excavated from the lower Middle Triassic (Anisian), from Luoping, Yunnan in southwestern China. Compared with all the hitherto known dinocephalosaurids and tanystropheids, this skeletally mature individual is exclusively similar to Dinocephalosaurus in a number of characteristics, particularly with the long posterodorsal process of the premaxilla extending posteriorly beyond the level of the external nares, the concave posterior margin of the anteroposteriorly broad quadrate, and the strongly expanded distal end of the chevron in most of the caudal vertebrae. However, this reptile is much smaller than Dinocephalosaurus and different from Dinocephalosaurus and the other dinocephalosaurid, Pectodens, in many aspects, such as an anteriorly tapering long rostrum, the dentition composed of short conical teeth with less heterodonty, relatively but obviously tall neural spines of the axis and the anterior cervical vertebrae. Our phylogenetic analysis suggests that the new archosauromorph is a dinocephalosaurid, and then we erect Austronaga minuta gen. et sp. nov. based on this specimen. Detailed comparisons in osteological anatomy and the discussion about its potential aquatic adaptation of this new taxon are also provided.
Key words: Luoping, Yunnan, East Tethys, Triassic, marine reptile, Archosauromorpha, Dinocephalosauridae, osteological anatomy
Diapsida Osborn, 1903
Archosauromorpha Huene, 1946 sensu Dilkes, 1998
Dinocephalosauridae Spiekman et al., 2021
Austronaga minuta gen. et sp. nov.
Etymology: Austronaga, from the Latin “auster” or “austral” meaning south or southern referring to the South China Block where this taxon occurred, combining with “naga”, an Asian mythological figure that is snake-like and associated with water; minuta meaning small refers to the relatively small body size of this animal compared with most of its Triassic marine archosauromorph relatives.
Wei Wang, Hong Lei and Chun Li. 2024. A small-sized dinocephalosaurid archosauromorph from the Middle Triassic of Yunnan, southwestern China. Vertebrata Palasiatica. DOI: 10.19615/j.cnki.2096-9899.231013
https://www.vertpala.ac.cn/CN/10.19615/j.cnki.2096-9899.231013
摘要：现在的中国南方地区在三叠纪时期曾位于特提斯洋东部。在该区域产出的众多海生爬行动物中，恐头龙(Dinocephalosaurus)的形态特化，颈部极度增长，可与时代略晚的长颈龙(Tanystropheus)相比拟。这两种爬行动物分别归属于恐头龙科(Dinocephalosauridae)和长颈龙科(Tanystropheidae), 而这两个科的成员加之另外一些基干物种代表了主龙型类(Archosauromorpha)中一系列早期分异出的支系。报道一件产自云南罗平地区中三叠世安尼期地层的主龙型类成年个体新标本IVPP V18579, 与目前已知的早期主龙型类成员相比，该标本显示出与恐头龙属一致但区别于其他属种的特征，主要包括前颌骨发育有超过外鼻孔后缘的较长后背侧突，方骨前后向较宽大且具有后边缘的凹缺，大部分尾椎上的人字骨带有远端前后向的延展。然而，新标本体型明显小于恐头龙，且显示出与恐头龙属和梳齿龙属(另一恐头龙科成员)不同的鉴别特征，例如吻部窄长、牙齿短锥状且异齿性弱、枢椎和前部颈椎的神经棘显著更高等。基于最新的用于早期主龙型类系统发育分析的特征矩阵，系统发育分析结果确定V18579代表一个新的恐头龙科成员，在恐头龙科中与恐头龙属互为姊妹群关系。于是基于V18579建立了一新属新种：玲珑南蛇龙(Austronaga minuta), 同时对其进行了详细的解剖学特征描述，并讨论了它可能具有的水生适应性。
关键词: 云南罗平, 东特提斯, 三叠纪, 海生爬行动物, 主龙型类, 恐头龙科, 骨骼学解剖
