The Impact of Bioturbation on Infaunal Ecology and Evolution during the Proterozoic-Cambrian Transition

Abstract

Terminal Proterozoic to lower Cambrian siliciclastic sequences in North Wales, Newfoundland, and Finnmark, Norway have been examined for evidence of changes in metazoan activity, based on ichnological data. Information was collected on infaunal tiering, age, evolutionary complexity, ichnofabric, and taphonomy. Averaged over lower Cambrian time, facies had little effect on size and faunal density of trace-making organisms. A landward shift in bioturbation intensity apparently occurred as larger organisms colonized firm muddy substrates on the inner shelf through time. In the earliest stage of the lower Cambrian, the majority of ichnodiversity relates to surface-feeding trace fossils. Not until the Tommotian is evidence for pervasive detritus feeding common. These changes were driven by evolutionary adaptation and external environmental forces. In addition, the activity of infaunal metazoans altered the intra-sediment environment in a manner that increased habitability and primary productivity in a way that encouraged further exploitation of sedimentary nutrients.