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