Terminal Ediacaran And Early Cambrian Tubular Fossils From Southern Shaanxi Province,South China

The life evolution history of the Ediacaran-Cambrian transition is one of the key evolutionary links in the whole process of the generalized “Cambrian explosion”.The fossil biota from the terminal Ediacaran and the early Cambrian are the direct and key evidences for the study of the evolution history of early life in this transitional geohistorical period.Traditional studies believe that there is evolutionary replacement between the fossil biota in the terminal Ediacaran and Early Cambrian,but recent research work shows that there is evolutionary continuity between some taxa in these two geological history periods.Specifically,there are some morphological similarities in some tubular fossils from the terminal Ediacaran and the early Cambrian.Therefore,there may be a closer evolutionary relationship between the tubular fossil biota in the terminal Ediacaran and early Cambrian,which needs further breakthrough in the research work.In this paper,we study the systematic paleontology of terminal Ediacaran and early Cambrian tubular fossils,which were recovered from the two Ediacaran-Cambrian boundary sections(Yuanbaoshan section and Shizhonggou section)in Ningqiang area of Southern Shaanxi,province preserved in three-dimension through phosphatization and silicification.The key points of this dissertation are summarized as following:1.Three species(C.hartmannae Germs 1972、C.ningqiangensis Cai et al.,2017、C.xuanjiangpingensis Cai et al.,2017)of terminal Ediacaran index Cloudina,and another important tubular fossil(Multiconotubus chinensis,Cai et al.,2017)were discovered from the top of Ediacaran Dengying Formation at Yuanbaoshan section.This discovery makes the Yuanbaoshan section the second fossil locality of Cloudina-Multiconotubus biological Assemblage in the world.2.At least four unnamed new types of tubular fossils have been discovered in the Beiwan member of the Ediacaran Dengying Formation at the Yuanbaoshan section.Some of the tubular fossils can be compared with the contemporary tubular fossils from the Three Gorges area of China and central Spain.In addition,these tubular fossils are similar to some tubular fossil taxa of early Cambrian in tube shape and size.3.We report a Sinotubulites-like fossil,Asperporella regularis gen.et sp.nov.,from the basal Cambrian Kuanchuanpu Formation at the Shizhonggou section in southern Shaanxi Province,South China.The newly discovered fossil shares striking similarities to terminal Ediacaran fossil Sinotubulites baimatuoensis in terms of the morphological characteristics but also,they are significantly different.The new discovery indicates evolutionary continuity of sinotubulitids across the Ediacaran-Cambrian boundary.4.A large number of tubular fossils with rich morphological types and fossils with other morphological characteristics have been discovered at the Cambrian Kuanchuanpu Formation of Yuanbaoshan section.After identification,it is considered that the fossil groups found at present mainly include: Anabarites,Protohertzina,Conotheca,Carinachites,Lopochites,Siphogonuchites,Olivooides.The Kuanchuanpu assemblage can be well correlated with the globally established Anabarites trisulcatus-Protohertzina anabarica Biozone.