Early-Middle Ordovician graptolite Phyllograptus from the Yiyang area, Hunan Province

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. 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.

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