贵州南部独山地区泥盆纪弗拉期的石燕贝类腕足动物

弗拉期是了解泥盆纪弗拉-法门灭绝事件之前古代生物多样性的一个关键阶段.贵州南部的独山地区因其所具有的完整层序及丰富的底栖牛物化石成为我国主要泥盆系参考剖面之一.独山剖面弗拉期的石燕贝类腕足动物至少包括5种类型,其中4种在本文中为首次描述和图示.Conispirifer之前只发现于欧洲及北美的弗拉期地层中,目前也首次在华南独山剖面的同期地层中发现.大多先前从贵州南部其他地区弗拉期地层中描述的多种Cyrtospirifer可归于Cyrtospirifer subextensoides新种内.鉴于前人对Emanuella的模式种E.takwanensis 的内部构造描述的矛盾状况,本文暂把研究区具有抬离壳面的纤细铰窝、固着于壳面的主突起以及其前方下面为外铰板支撑的标本归于E.takwanensis.在华南弗拉期可初步识别出三个腕足动物群组合带:Yocrarhynchus-Phlogoiderhynchus动物群以小嘴贝类-无洞贝类-双腔贝类腕足动物为特征,其时代大致从弗拉阶底部至Pa.punctata带;之后为Cyrtospirifer动物群,以Cyrtospirifer的存在为特征,又可分为早晚两部分,前者(未命名)以conispiriferid类的Conispirifer和Pyramidaspirifer、弓石燕类、无洞贝类等为特征,其时代大致为Pa."hassi"带至下Pa.rhenana带;后者为Hunanotoechia动物群,以丰富的小嘴贝类-无洞贝类.弓石燕类腕足动物为特征,其时代大致为上Pa.rhenana带至Pa.1inguiformis带.

SPIRIFERIDE BRACHIOPODS FROM THE FRASNIAN (DEVONIAN) OF THE DUSHAN AREA, SOUTHERN GUIZHOU, CHINA

The Frasnian is a critical time interval for understanding paleodiversity variation before the Devonian Frasnian-Famennian mass extinction event. The Devonian sequence in the Dushan section of southern Guizhou is nearly complete with abundant benthic fossils, and is regarded as one of the Devonian reference sections of China. The spiriferide brachiopods in the Frasnian of the Dushan section include at least five species, of which four (including one new) are described and illustrated for the first time in the present paper. Conispirifer, a genus known in Europe and North America, is discovered for the first time in South China. Most of previously described Cyrtospirifer species from the Frasnian of southern Guizhou are referred to Cyrtospirifer subextensoides n. sp.. The nature of the cardinal process is not definitely known in the type species of Emanuella, E. takwanensis (Kayser, 1883) and, therefore, specimens from the study area with a weak, elevated socket, an anteriorly developed supporting plate (=outer hinge plate), and a fixed cardinal process are tentatively assigned to E. takwanensis. Three brachiopod assemblage zones may be recognized for the Frasnian of South China: the Yocrarhynchus-Phlogoiderhynchus assemblage that is characterized by rhynchonellide-atrypid-ambocoelid brachiopods (spanning approximately the base of the Frasnian through the Pa. punctata Zone); thereafter the Cyrtospirifer assemblage may be divided into two parts: the early part (un named) is characterized by the presence of conispiriferid Conispirifer and Pyramidaspirifer, cyrtospiriferids, atryp ids and others (spanning approximately the Pa. "hassi" Zone through the Lower Pa. rhenana Zone), and the late part ( Hunanotoechia assemblage) is characterized by abundant rhynchonellide-atrypid-cyrtospiriferid brachiopods (spanning approximately the Upper Pa. rhenana Zone through the Pa. linguiformis Zone).