Three tubular fossil assemblages from the terminal Ediacaran Dengying Formation in southern Shaanxi Province of South China

Abstract

Terminal Ediacaran fossils (ca. 550–539 Ma) contain potentially the earliest known animals. Tubular fossils represent a characteristic fraction of terminal Ediacaran fossil forms and they may have served as evolutionary ancestors of the subsequent diversification of tubular taxa in the early Cambrian. However, the paleogeographic range of previously reported terminal Ediacaran tubular taxa and those undescribed tubular forms locked in the fossil record, remains poorly documented. Our presentation illustrates three fossil assemblages from the Ediacaran Denying Formation at the Shengchangba section in southern Shaanxi Province, South China. The stratigraphically lower assemblage consists primarily of pyritized tubular fossils Conotubus and Gaojiashania in siltstone–mudstone beds, the middle assemblage is composed of calcified Cloudina and at least four tubular forms in massive limestone beds, whereas the higher assemblage is made up of silicified Cloudina, Sinotubulites, and several new tubular forms in thick-bedded dolomite. In addition to Cloudina, Sinotubulites, Conotubus, and Gaojiashania, several variety tubular forms—including densely and irregularly annulated conical tube and straight tube, unevenly undulated tube, irregularly ribbed conical tube, cylindrical tube with regularly spaced transverse ridges and single-walled conical tube with smooth outer wall—are identified in the Dengying Formation. The new occurrences of previously reported taxa broad geographic range of Cloudina, Sinotubulites, Conotubus, and Gaojiashania. Although the taxonomic affinities and phylogenetic relationships of these fossils remain problematic due to the absent and/or poor preservation of anatomical details, the several varieties unamend tubular forms add to the diversity of terminal Ediacaran tubular fossil biotas. The co-occurrence of Cloudina hartmannae with diverse tubular fossil forms plays an important role in facilitating global biostratigraphic correlation. Pyritization in the siltstone–mudstone facies, calcification in the limestone facies and silicification in the dolomite facies, responsible for the exceptional preservation of the three tubular fossil assemblages, provide revelatory clues in recovering new fossil localities.