峡东地区寒武纪水井沱组下段双瓣壳类节肢动物系统古生物与个体发育研究

Taxonomy and ontogeny of bivalved arthropods from the lower member of the Shuijingtuo Formation, Series 2 and Stage 3, Eastern Three Georges Area, South China

双瓣壳类节肢动物在全球寒武纪海洋中广泛分布,是寒武纪时期布尔吉斯页岩型化石生物群的重要组成类群和典型代表。它们的起源、演化及生态学研究是对早期后生动物演化研究的重要内容。本文详细描述了峡东地区寒武系第二统第三阶水井沱组下段两种双瓣壳类节肢动物,Caudicaella bispinata(Cui and Huo,1990)comb.nov.和Sunella grandis Huo,1965。依据新建的Caudicaella属征,对孙氏虫科的鉴定特征进行了修订。首次研究了孙氏虫科两属种壳瓣的生长发育模式,揭示了壳瓣高长比的等速生长和C.bispinata基刺相对于壳长的异速生长关系。元素扫描分析研究表明,长阳地区天柱山村剖面化石为碳质压膜保存。功能形态学研究认为,C.bispinata是远洋浮游型生物,其广泛的古地理分布有望为寒武纪早期全球生物地层对比提供新的化石依据。

Bivalved arthropods were widely distributed in the Cambrian ocean and an important component of the arthropods in the Burgess Shale-type Lagerst?tten.In this study,based on over 260 specimens,two bivalved arthropods,Caudicaella bispinata(Cui and Huo,1990)comb.nov.and Sunella grandis Huo,1965,were described from the Cambrian Shuijingtuo Formation,Series 2 and Stage 3,South China.Both genera are assigned to the emended family Sunellidae Huo,1965.C.bispinata is characterized by elongated cardinal spines,semicircular valves with dilated doublure and a distinctive anterodorsal sulcus.Sunellidae was revised,with newly identified features such as an anterodorsal sulcus extending from the middle of the anterior spine to the anteromedian part of the carapaces.Statistic and ontogenetic analyses indicate the valves of both genera grow isometrically,while cardinal spines of C.bispinata grow allometrically.Analyses using EPMA-WDS has revealed that fossils from the lower Member of the Shuijintuo Formation in Changyang area were preserved as pristine carbonaceous film.Functional analogy suggests a pelagic lifestyle of C.bispinata.In addition,the palaeogeographic distribution model of C.bispinata is helpful for a global biostratigraphical correlation in the Cambrian Period.