Garden of Ediacara and the Cambrian Revolution
Extended Abstract – Prato 2004

A. Seilacher
Dept of Geology, Yale University, P.O. Box 208109, New Haven CT 06520
Email:geodolph@tuebingen.netsurf.de
and
Tübingen University, Tübingen, Germany

Number of Words: 200
Number of References: 0
Number of Figures: 0 
Number of Tables:  0

Running header text: Garden of Ediacara 

The Ediacaran is set apart from all later periods by its unique ecological power structure. The rulers, in terms of biomass, body size, and morphological diversification, were giant plasmodial protozoans (Vendobionta and Xenophyophoria) that lived in benthic environments structured by microbial (largely cyanobacterial) mat grounds. Like mammals in the time of dinosaurs, early metazoans lived in the shadow of these unicellular giants. While later ecosystems owe their incumbency largely to balanced trophic relationships, the equilibrium in the "Garden of Ediacara" may have been maintained solely by productivity, chemodefense and microbial parasites, i.e. by factors that left no traces in the fossil record.
The Cambrian Revolution put an end to this peaceful world. It led to the explosive radiation of animals, now equipped with mineralized and readily preservable skeletons. The burrowing programs recorded by trace fossils show a similar radiation, in spite of being made by soft-bodied animals. At the same time, the onset of vertical bioturbation transformed the ubiquitous matgrounds into soft mixgrounds. Thereby the former rulers were driven to extinction or exiled into deep-sea refugia. While multiple changes were bundled in shallow seas, deep-sea ichnofaunas suggest that the Cambrian radiation of metazoans and the agronomic revolution were independent events.