Radiolarians from Early Cambrian in South China

In the study on the evolution of life and environment during the Cambrian, multiple species of or-ganisms have emerged explosively and evolved rapidly. Previous studies on Marine benthic ecosystems have been extensive, and the sequence of the first emergence of animal phyla during the Cambrian explosion has been basically identified, and the tree of early animal evolution has been constructed. However, few studies on plankton ecosystems have been conducted. As an important part of the plankton ecosystem, the study of the early Cambrian radiolaria is of great significance for understanding the composition of the early Marine plankton ecosystem and the manifestation of the Cambrian biological explosion in the plankton ecosystem. Therefore, in recent years, the study on the evolution of early Cambrian radiolaria has been a hot spot, especially in the last decade, more discoveries have been made in the early Cambrian radiolarian. Controlled by tectonic processes, South China undoubtedly had a strong advantage in the Cambrian period, and a large range of sedimentary strata from Ediacaran to Cambrian have been completely pre-served, and the evolution events of different biological types under different environments have been rec-orded to a great extent in this important period. It is known that radiolaria with spherical shells have been widely distributed in shallow - water to deep - water facies in South China since the Early Cambrian period, but there is a big difference in species and abundance between the radiolaria fossils reported in the Early Cambrian and the middle-late Cambrian. Previous radiolarian studies in the early Cambrian in South Chi-na initially focused on Yanjiahe Formation (Chang et al., 2018), Shujingtuo Formation (Ma et al., 2019) in western Hubei Province and Xintangwuhetang Formation in western Zhejiang Province (Braun et al., 2007; In the carbonaceous shale of Zhang et al., 2013, although radiolarian species of different genera have been reported in the siliceous rocks of Niujiaohe Formation in southern Jiangxi in the deep-water environment in recent years, fewer radiolarian species have been reported in the Niujiaohe Formation in southern Gannan compared to the Shuijingtuo Formation in western Hubei at the same time. Only Zhang and Feng (2019) and Zhang et al. (2021) have reported the radiolarian fauna of the Niujiaohe Formation in detail, and no systematic reports have been made on the radiolarian fossil record of the Cambrian Niujiaohe Formation in southern Jiangxi Province. Therefore, in order to enrich the early Cambrian radiolarian fossil materials, the study of radiolarian fauna in Chongyi area of southern Jiangxi Province is systematically dis-cussed, and the possible evolutionary model of early Cambrian radiolarian is explored. Based on the taxonomic study of radiolarian fossils of early Cambrian Niujiaohe Formation in Chongyi area of southern Jiangxi Province and the comparison of radiolarian species and production environment in South China, the following conclusions are drawn: (1) The radiolarian fossils reported in South China are preliminarily summarized according to the structural division of deep and shallow water. The results show that there are 6 genera and 7 species of radiolarian fossils reported in relatively shallow water sedimentary areas, while only 3 genera and 3 species of radiolarian fossils reported in relatively deep water areas. The size of radiolarian fossils in shallow water areas is significantly larger than that in deep water areas. Therefore, by comparing the diversity and overall characteristics of different radiolarian fauna in deep and shallow water areas, the evolutionary diversity of radiolarian fauna in deeper water areas is low, which is accompanied by the characteristics of smaller individuals. So we speculate that radiolaria probably originated in shallow water area and evolved from shallow water to deep water area gradually. (2) So far, combining the existing data and the results of this study, the radiolarian fauna in South China is composed of 7 genus taxa, 7 genera and 9 species (Kalimnasphaera sp., Tetrasphaera? sp., Paraantygoporaporosa, Paraantygopora sp., Spherical radiolaria, Beothuka sp. Blastulospongiapolytreta, Blastulospongia sp., Braunosphaerasinensis). Although the research on the early Cambrian radiolaria is not perfect, combined with relevant data in South China, radiolarian fauna began to exhibit diversity and complex morphology, indicating the presence of various advanced spherical skeletons in early radiolarians, and radiolarians from the early Cambrian appeared to display multiple evolutionary trends (Huang et al., 2025). This study was supported by the National Natural Science Foundation of China (NSFC) (42462001) and Guangxi Natural Science Foundation (2023GXNSFBA026273).