Diversity and Taphonomy of Early Metazoan Embryos
Extended Abstract – Kyoto 2006

Chia-Wei Li
Department of Life Science, National Tsing Hua University, Hsinchu, Taiwan 
(email: lslcw@life.nthu.edu.tw)

Number of Words: 359
Number of References: 0 
Number of Figures: 0 
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Running header text: Early Metazoan Embryos

Abundant fossilized metazoan embryos from the terminal Proterozoic and the Early Palaeozoic of China have been reported since the 1990s. The three-dimensional preservation of the embryos down to the cellular level provides the opportunity of determining their affinities with modern forms. Identifying the diversity of these embryos may revolutionize palaeontological insight into the evolutionary origins of animal forms.
In this report the representative embryos from the following three localities are illustrated:
•	The Doushantuo Formation at Weng’an, Central Guizhou, 580 Ma. This is the fossil site with the oldest known metazoans. Numerous eggs, embryos, and larvae were densely packed in the phosphate deposit. Small numbers of microscopic adult forms of sponges, hydrozoans, anthozoans, and bilaterians were also found. 
•	The Kuanchuanpu Formation at Kuanchuanpu, Southern Shanxi, 540 Ma. This earliest Cambrian stratum contains a diversity of phosphatized embryos with tetramerous, pentaradial, and bilateral symmetry with small shelly fossils having affinities to a variety of metazoan clades, including cnidarians, ecdysozoans, and lophotrochozoans.
•	The Kaili Formation at Kaili, Eastern Guizhou, 510 Ma. This Middle Cambrian stratum records more than 120 metazoan genera, commonly preserved as organic carbon films. A dozen clusters of three-dimensionally preserved putative trilobite eggs and embryos were found recently.  
Developing a non-invasive methodology to determine the internal fine structures of the exquisitely preserved embryos is crucial, especially for the rare and problematic ones. Synchrotron x-ray microscopy (SXM) is ideal for this purpose. The SXM produces three-dimensional images by taking radiographic images at different sample orientations with respect to the synchrotron x-rays, and a filtered back projection tomography reconstruction algorithm is applied to produce the solid model with a resolution of about 1 µm. The application of SXM revealed the body fossil of a parasitic nematode-like bilaterian (several mm long) living in the Doushantuo embryos, and the early developmental stages of the putative Kaili trilobites.
     Understanding the process that led to the phosphatization of the Doushantuo fossils is essential in order to determine the Precambrian marine environment, the catastrophe, and the subsequent taphonomy. Here, we show that rapid and extensive phosphatization of modern seaweeds and coral tissues is possible under laboratory conditions without the involvement of microbial activity.