华东志留纪最早期的华夏正形贝动物群及其宏演化意义

THE EARLIEST SILURIAN CATHAYSIORTHIS FAUNA(BRACHIOPODS) OF E CHINA AND ITS EVOLUTIONARY SIGNIFICANCE

志留纪最早期的腕足动物群在文献中很少记录,与标准笔石相伴者更为稀罕。江西玉山志留系底部因发现Akidograptus ascensus带的笔石而确定该处盛产志留纪初期(鲁丹早期)、多样性较高的腕足动物群。根据组成、性质与层位,它与浙江江山、常山、淳安、余杭等7个地点的同期组合可统一命名为华夏正形贝动物群(Cathay-siorthis Fauna)。它包含了不同群集,都产自细碎屑岩(如泥岩)中,其分布主要受海水深度和距华夏古陆远近的控制。这个动物群生长在奥陶纪大灭绝后的残存期,文章探讨了它的残存特征。研究揭示,奥陶纪末大灭绝对腕足动物演化的一个实质性的贡献在于制约了奥陶纪占优势的A组(正形贝/扭月贝大类群:发育铰合面、窗齿型铰齿、正扭型主突起和简单腕器官)的繁盛态势,滋生了B组(五房贝/无洞贝大类群:发育后转面、弓齿型铰齿和复杂腕器官但缺失正扭型主突起)在志留纪的优势,造成腕足动物宏演化历程中的一次重大转折。文中提出"优势替代滞后型式(Pattern of lag of dominance replacement)",专指A组类群的优势被B组类群替代的时间不是紧跟在奥陶纪末大灭绝之后,而是距大灭绝结束约4Ma之后。文中描记新属华夏正形贝(Cathaysiorthis gen.nov.)。

Summary Since a preliminary investigation Rong and Zhan （2006）, more material carried out by of the brachiopods have been collected from the basal part of the Shiyang and Anji formations at various localities in northeastern Jiangxi and western and northern Zhejiang provinces during the past five years. These brachiopods are of earliest Rhuddanian in age （Akidograptus ascensus Biozone）. Twenty three species of 23 genera belonging to 20 families of the brachiopods are identified, including Paracraniops, Deliella , Katastrophomena , Leptaena , Tashanomena , Eopholidostrophia , Eoplectodonta, Leangella, Skenidioides, Hesperorthis, Glyptorthis, Cathaysiorthis gen. nov. , Dalmanella, Levenea, Epitomyonia, Coolinia, Triplesia, Brevilamnulella, Thebesia, ？ Alispira, Eospirigerina, Hyattidina and Eospirifer, in addition to Yushanomena which was described by Zeng and Hu（1997）from this assemblage is considered to be a junior subjective synonym of Tashanomena Rong and Zhan, 1994. However, we have not found Tashanomena in the new collections.