西藏晚二叠世四射珊瑚Ipciphyllum naoticum的鳞板特征兼论喷口构造的分类意义

Ipciphyllum是中国中晚二叠世地层中最常见的块状复体四射珊瑚, Ipciphyllum naoticum是该属中唯一发育喷口构造的种。通过对采自西藏札达姜叶玛剖面上二叠统姜叶玛组的Ipciphyllum naoticum进行连续切片, 研究其鳞板特征, 发现横切面上鳞板形态在个体发育的不同阶段变化明显, 包括喷口(庙宇状)鳞板、弧形板片状鳞板和偶现的侧鳞板等, 表明同一种内鳞板的形态多变, 以某一特殊形态的鳞板作为种一级甚至更高级的分类标准值得商榷。结合前人对喷口鳞板的发育可能与相对高能的水环境有关, 分类意义不应超过种级的研究结论等, 建议废除以喷口鳞板(构造)作为重要分类特征的Protonaoticophylidae科和Protonaoticophylinae亚目。

Dissepimental Characteristics of the Late Permian Rugose Coral Ipciphyllum naoticum with Discussion on the Taxonomic Significance of Naotic Structure

Ipciphyllum, which is a dissepimental, colonial rugose coral representative of the Waagenophyllinae, is one of the most diversified and abundant genera in the Permian Maokou Formation in South China. Ipciphyllum naoticum from the Late Permian Gyanyima section in Tibet, southwest China is the only species in Ipciphyllum that develops naotic dissepiments. In this study, the dissepimental shapes of Ipciphyllum naoticum in different ontogeny stages can be observed in detail with serial transverse sections. In the embryonic and neanic stage, septa strongly thickened in peripheral part. Concentric dissepiments inconspicuously developed in the middle part in transverse section. In the adult stage, septa become thin in peripheral part and obviously thinner than that of the central part within the tabularium. Dissepiments developed at the base of partial septa. Firstly, these dissepiments partly appear as arc-shaped plates, and then some arc-shaped plates overlap each other and form naotic structure. The lateral dissepiments sporadically appear in this later stage. The dissepiments of the same species are various in shape, so it is not suitable to regard one special shape of dissepiments such as arc-shaped plates, or naotic structure as species character or even higher classification standard. Pervious study about the Permian naotic-dissepiment rugose corals in China implies that naotic-dissepiment development was probably related to enhanced hydrodynamic force. Naotic dissepiments are not of higher taxonomic significance than species level. On this basis, combined with various shape of Ipciphyllum naoticum, this paper suggests that Protonaoticophylidae and Protonaoticophylinae with naotic structure (dissepiments) as the important classification characteristics should be abandoned.