Network Analysis of Fossil Co-occurrence in the Ediacaran and Paleozoic

Abstract

Upper Neoproterozoic successions around the world contain a number of recurrent macrofossil assemblages, generally distinguished according to Ediacara-type and early skeletal fossils. These assemblages represent potential biozones, pertinent to the subdivision and correlation of the Ediacaran system, and record patterns in biologic turnover through space and time, including a change in communities interpreted as a result of the earliest mass extinction. To contribute to our understanding of these assemblages, we compiled a dataset of body and trace fossil occurrences, which expands on previous compilations in terms of overall size and geographic, stratigraphic, and taxonomic comprehensiveness. We then analyzed this new dataset by applying methods rooted in network theory. These methods include powerful techniques for visualizing co-occurrence data (e.g. interactive force-directed network visualizations) and numerous approaches to defining and detecting communities within networked systems. We present the results in conjunction with relatively straightforward case studies of animal fossil occurrence in the Paleozoic. Altogether, our work reveals major and previously overlooked patterns in co-occurrences of Ediacara-type fossils, carbonaceous compressions, skeletal fossils, and assorted tubular remains, and traces in the Neoproterozoic. These results have implications for biostratigraphy and paleoecology, providing new insights into the macrofossil assemblages of the Ediacaran, their total number, taxonomic makeup, and facial, stratigraphic, and taphonomic overlap.