A Revised Morphology of Cloudina with Ecological and Phylogenetic Implications

The conventional view of the Ediacaran index fossil Cloudina, as proposed by Grant (1990), depicts the shell structure as a series of nested test tubes. A digital serial-reconstruction of Cloudina and examination of thin sections indicates that only the bottom-most tube has a bottom and that the shell wall structure is not as well defined as previously thought. The conventional ecological reconstruction, as proposed by Seilacher (1999), puts Cloudina in a microbial mat framework. Evidence from fossils in situ and from the shape of Cloudina suggests that this interpretation is incorrect. Rather, I propose that Cloudina lived on seaweeds in the reef environment. I also introduce a new mode of inference in determining shell orientation based on gravitational forces. Given the morphological evidence, Cloudina appears to be more similar to pogonophoran or annelid worms and less similar than previously thought to cnidarian corals.