Paleobiology, Biostratigraphy, and Taphonomy of Neoproterozoic Eukaryotes and Cambrian Animals with Carbonaceous Preservation

Carbonaceous fossil preservation is an important taphonomic window that provides critical perspectives on the evolutionary history of life. However, phylogenetic interpretation of carbonaceous fossils is not straightforward. This is largely because critical biological information is usually lost during fossilization and three-dimensional morphologies are flattened into two-dimensional compressions. Hence, innovative techniques and methods are required in order to better understand the evolutionary significance of these fossils. To achieve this goal, this dissertation is focused on using an array of innovative research techniques to investigate the paleobiology, biostratigraphy, and taphonomy of carbonaceous fossils in critical times of early life evolution, including Neoproterozoic and Cambrian. Chapters 2 to 5 in this dissertation present original research that helps to decipher hidden biological structures of various carbonaceous fossils using a series of research methods. An improved understanding of these carbonaceous remains will ultimately advance our knowledge regarding the early evolutionary history of life on Earth.

Chapter two describes new cellular structures of the carbonaceous compression macrofossil Chuaria using backscattered electron scanning electron microscopy. The data show that Chuaria, which is one of the most common fossils in Neoproterozoic and whose phylogenetic interpretation has been uncertain, is likely a multicellular eukaryote. Chapter three is aimed to resolve a long debate on the depositional age of the Gouhou Formation in the Huaibei region of North China and to constrain the Precambrian-Cambrian (P-C) boundary in this area. Using a low manipulation maceration technique, this study reveals a diverse assemblage of organic-walled microfossils from the lower Gouhou Formation, suggesting that the lower Gouhou Formation is Tonian in age and the P-C boundary may be located within the Gouhou Formation. Chapter four reports a group of problematic carbonaceous compression macrofossils from the Hetang Formation in South China. Taphonomic analysis using optical and electron microscopy tentatively suggests that these carbonaceous macrofossils are probably carapaces of bivalved arthropods. The last chapter describes a group of sponge fossils with carbonaceous preservation from the early Cambrian Hetang Formation in South China. Using an array of electron microscopy techniques, this study reveals that siliceous spicules of the Hetang sponges have large axial filaments and large proportions of organic material, suggesting early sponge in the Precambrian and Cambrian may have had weakly mineralized or entirely organic skeletons. Results from this study helps to reconcile the apparently conflicting molecular clocks, biomarker fossils, and spicular fossils of early sponges.