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42231-AC8
Paleobiology, Paleoecology, and Taphonomy of a Recently Discovered Burgess Shale-Type Lagerstatte in Early Cambrian Black Shales

Shuhai Xiao, Virginia Polytechnic Institute and State University

The primary objectives of this project are to collect paleontological, sedimentological, and geochemical data, and to analyze the paleodiversity, paleoecology, and paleoenvironment of the early Cambrian Hetang assemblage in South China. We have completed a systematic investigation of the Hetang biota. Together with geochemical and sedimentological data, we were able to understand the taphonomy of exceptionally preserved sponge fossils in the Hetang biota.

During the implementation of this project, we expanded our investigation of early Cambrian paleobiology and initiated a systematic study of earliest Cambrian phytoplankton fossils. The goal is to test whether the radiation of phytoplankton is temporally coupled with the radiation of filter-feeding animals. The temporal relationship between phytoplankton and animal radiations in the earliest Cambrian provides key paleontological evidence to test the possible ecological linkage between Cambrian phytoplankton and animal radiation (Butterfield, 2001). We are currently in the process of analyzing the micropaleontological data collected from early Cambrian rocks in South China.

In addition, we investigated a silicified Ediacaran assemblage that contains two enigmatic fossils: Horodyskia and Palaeopascichnus. The interpretation of these two fossils has been very controversial, ranging from giant single-celled organisms, to tissue-grade animal-like organisms, to animal meandering traces. If they are indeed animal fossils or animal traces, they would have important implications for the early history of animal evolution. Unfortunately, previously reported fossils of these two genera are preserved as casts or molds in coarse-grained sediments, thus the morphological resolution of these fossils is very poor. The new fossils, collected from Ediacaran cherts from South China, offer unprecedented resolution for the morphological interpretation of these two genera because they are silicified by early diagenetic, fine-grained silica. Our preliminary results conclusively falsify the animal trace interpretation, and provide some support for a morphological comparison with modern single-celled organisms such as foraminifers.

Together, these studies significantly enrich our knowledge about the early evolution of animals and other life forms at the Ediacaran-Cambrian transition.

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