Nail-shaped sclerite fossils from the Cambrian Gezhongwu Formation in Zhijin County, Guizhou Province
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Abstract:
Nail-shaped sclerites are common small shelly fossils (SSFs) with mineralized sclerites in the early Cambrian strata of South China. In this paper, we focus on the systematic study of the nail-shaped sclerites from the Gezhongwu Formation in Zhijin County, Guizhou Province. The results show that these nail-shaped fossils are mainly composed of zhijinitids and problematic cambroclavids. They include nine species in four genera with some taxa first found in Zhijin County, such as Zhijinites tumourifomis, Z. lubricus, Z. clavus, ?Deiradoclavus sp. and ?Cambroclavussp. Based on observations of their preservation modes and morphology, we find that different nail-shaped fossil species have different structures, such as the contracting inner wall of the spine and the vertically crossed fibers in some specimens of Zhijinites and the concave structure on the bottom surface of the plates of many Zhijinites species, indicating morphological similarities and variations in different genera and species. Analysis of the spatial and temporal distributions of these nail-shaped sclerites suggests that they first occurred in the Zhijin area, then radiated and spread to other areas of the Yangtze Platform and adjacent landmasses. In addition, this problematic cambroclavids from the lower part of Gezhongwu Formation may represent the earliest record of this group and extends its age to the Fortunian, providing new important information for the discussion of their evolution and stratigraphic significance.
