贵州中三叠世盘县动物群比耶鱼属未定种的发现及其意义

记述采集自贵州省盘县中三叠统安尼阶关岭组上段盘县动物群的一件仅残存尾部的比耶鱼标本。这是比耶鱼在该动物群的首次报道, 也是目前比耶鱼在中国地质时代最早的化石记录。依据标本个体大、仅尾上叶及尾柄后缘背侧覆盖有狭长条状且缺失硬鳞质的鳞片、尾部发育单个愈合的神经棘和脉棘、尾鳍背缘棘鳞发育等特征, 将其归入比耶鱼属。同时, 该标本以个体更大(推测身长超过2 m)、尾下骨更多(9 根)、尾下叶棘鳞发育以及上、下叶外缘交角超过 70°等特征, 不同于已报道的其他比耶鱼物种。但是, 考虑到标本信息有限, 暂定为比耶鱼未定种Birgeria sp.。比耶鱼是仅见于三叠纪海洋中的全球性分布的大型肉食鱼类, 其在盘县动物群中的首次发现丰富了该动物群鱼类多样性, 增加了其群落生态结构的复杂性。基于当前化石发现的情况, 认为比耶鱼在东特提斯生物区(中国)较西特提斯生物区的出现可能更晚, 前者最早的化石记录见于中三叠世安尼期, 而后者最早见于早三叠世史密斯亚期。

Discovery and Its Significance of Birgeria sp.from the Middle Triassic Panxian Fauna,Guizhou Province,China

A large-sized caudal fin of the actinopteryigan Birgeria, from the Middle Triassic (Pelsonian, Anisian) Panxian Fauna in the Upper Member of the Guanlin Formation, Panxian County, Guizhou Province, China is described. It is the first report of Birgeria in the Panxian Fauna and represents the earliest fossil record of Birgeria in China. There are some specialized characters for this specimen in accordance with Bigeria: the speculated large size, narrow scales without ganoine ornament merely covering the posterodorsal portion of the caudal peduncle and the axial lobe of the caudal fin, single neural spine and haemal spine in caudal region, fulcra scales developed on the dorsal margin of the caudal fin, etc, which support the assignment of the current specimen to the genus Birgeria. Moreover, it distinguish from all known Birgeria species in its relatively large size (speculated total length over 2 m), a higher number of hypural (9), fulcras of the ventral margin of the caudal fin more developed and a bigger angle between the posterior margin of upper lobe and that of the lower lobe (>70º), but, a Birgeria sp. instead of a new species of Birgeria is assigned herein due to limited material. Birgeria is a kind of large carnivorous fish exsisting only in the Triassic ocean, which can be found from the Anisian Panxian Fauna to the Carnian Guanlin Fauna. The first appearance of Birgeria in China is later than that in West Tethys in Smithian, Early Triassic.