云南罗平中三叠世意外裸鱼的再研究

Re-study on Gymnoichthys inopinatus from Middle Triassic of Luoping, Yunnan, China

意外裸鱼(Gymnoichthys inopinatus)于2010年由Tintori等首次记述并归入基干新鳍鱼类。依据在云南省曲靖地区罗平县大凹子村中三叠世关岭组二段发现的新材料,对意外裸鱼进行了补充描述,并重新讨论了其系统发育关系。在意外裸鱼的新标本上,可见其续骨前端很可能与关节骨相关节,并有确切无疑的单一辅上颌骨,表明意外裸鱼应为鲱亚部(Halecomorphi)鱼类。此外,意外裸鱼的体表无鳞、椎体未骨化、髓棘和髓弓的结构和排列方式以及牙齿和尾脉棘的形状都与金尾鱼超科鱼类(caturoids)一致。系统发育分析结果表明意外裸鱼属于金尾鱼超科的基干类群。之前金尾鱼类主要见于欧洲和北美的侏罗系,现在公认的金尾鱼超科鱼类主要包括Liodesmidae中的Liodesmus属和金尾鱼科(Caturidae)中的Caturus和Amblysemius两属。意外裸鱼的发现不仅使金尾鱼类的出现提前了40Ma,而且填补了我国相关材料的空缺。

Gymnoichthys inopinatus was initially described by Tintori et al. in 2010, and regarded as a basal neopterygian. According to the new material of the Middle Triassic Guanling Formation discovered in Dawazi Village, Luoping County, Yunnan Province, China, we redescribed G. inopinatus, and re-identified its systematic position. G. inopinatus has only one supramaxilla and its symplectic is likely jointed with the articular, which are the identifying characters of Halecomorphi. Morever, G. inopinatus has no scales, its vertebral centra are not ossified, and the structure and relationship of the neural arches and neural spines, as well as the shape of teeth and ural haemal spines in G. inopinatus are quite like that of the caturoids. Hence, it is suggested to consider G. inopinatus as a basal form of the superfamily Caturoidea. Previously, caturoids were only discovered in the Jurassic of Europe and North America, and its recognized forms included Liodesmus, the only genera of the family Liodesmidae, and Caturus and Amblysemius of the family Caturidae. Gymnoichthys inopinatus is not only the first caturoid found in China, but also the earliest caturoid in the world, which is 40 million years earlier than the European and North American caturoids.