INTERPRETING COMPLEXITY OF TRACE FOSSILS FROM THE LATEST NEOPROTEROZOIC NAMA GROUP, NAMIBIA

The Ediacaran-Cambrian transition is one of the most dramatic geobiological intervals in Earth history, encompassing the extinction of the Ediacaran biota, the Cambrian explosion, and the ‘agronomic revolution’. While the complexity of ichnogenera in the Ediacaran is not nearly as great as in the Cambrian, there is nevertheless a large diversity of trace fossils reported from the terminal Ediacaran, particularly from Namibia. These trace fossils dominantly record horizontal locomotion; however, there also have been reports of more complex, vertical burrows, which would record the evolution of metazoans with musculature, and potentially a more diverse suite of feeding modes. Here we present preliminary data from ongoing work that is mapping and describing both ichnofossils and –fabrics in terminal Ediacaran strata, from a wide variety of sedimentary facies in the Nama Group of sediments in southern Namibia. In particular, we focus on small, vertical burrow ‘pairs’ which have previously been described as the u-shaped dwelling burrow Diplocraterion, but which were recently reinterpreted as small Conichnus. A third possible interpretation is that these represent abiogenic fluid- and gas-escape structures, which have been shown to share many common sedimentological characteristics with vertical trace fossils. Correctly discriminating between these three interpretations for these structures is key to establishing rates of metazoan evolution, the intensity of metazoan ‘ecosystem engineering’ prior to the Cambrian explosion, and determining proposed drivers for the extinction of the Ediacara biota.