湖南益阳早、中奥陶世的叶笔石属(Phyllograptus)

EARLY-MIDDLE ORDOVICIAN GRAPTOLITE PHYLLOGRAPTUS FROM THE YIYANG AREA,HUNAN PROVINCE

报道湖南益阳早、中奥陶世的叶笔石1属5种,包括Phyllograptus anna Hall,1865,Phyllograptus anna longus Ruedemann,1947,Phyllograptus anna ultimus Ruedemann,1904,Phyllograptus claviger Monsen,1937,Phyllograptus claviger acuminatus(Chen and Xia),1979。研究表明,该属主要产出于弗洛晚期至大坪中期,在早、中奥陶世笔石多样性演变事件第一阶段的后期(Corymbograptus deflexus带),叶笔石所代表的上攀伸展类型就已萌芽,且在第二阶段(Pseudophyllograptus angustifolius elongatus带-Isograptus victoriae divergens带)于均分笔石动物群中占据优势地位,对该动物群内部类群的演替起着承前启后的作用,同时也验证了笔石动物群自身的演替对于其多样性演变具有重要影响。

Five species of Early-Middle Ordovician graptolite genus Phyllograptus are reported from the Nanba section in the Yiyang area, Hunan Province,South China,including Phyllograptus anna Hall,1865,P.anna longus Ruedemann,1947,P.anna ultimus Ruedemann,1904,P.claviger Monsen, 1937, and P. claviger acuminatus(Chen and Xia),1979.This study indicates that Phyllograptus is distributed in the interval from the upper Floian to the middle Dapingian of Ordovician.As the early indicator of graptolite with scandent stipes,this genus first appeared at the end of the first phase(Corymbograptus deflexus Biozone)of graptolite diversification during the Early-Middle Ordovician,and became increasingly dominant in the Dichograptid fauna during the second phase(Pseudophyllograptus angustifolius elongatus Biozone-Isograptus victoriae divergens Biozone),directly affected the replacement between different groups within the Dichograptid fauna,implying that the evolution within the Dichograptid fauna significantly contributed to the graptolite diversification during the Early-Middle Ordovician.