SPATIAL POINT PATTERN ANALYSIS OF OBAMUS CORONATUS FROM NILPENA EDIACARA NATIONAL PARK, SOUTH AUSTRALIA

The spatial distribution of in situ sessile organisms can reveal information about their reproductive methods, life habits, and ecology. At Nilpena Ediacara National Park, South Australia, the exquisite preservation and excavation of 40 bedding planes from the Ediacara Member reveals in situ communities of the Ediacara Biota. Obamus coronatus is a recently described sessile, torus shaped fossil from the Ediacara Member of the Rawnsley Quartzite. This enigmatic taxon lived embedded in the organic surface which covered the seafloor during the Ediacaran. At Nilpena Obamus occurs on four beds, one dominated by nearly 100 specimens, providing an opportunity to examine the spatial distribution of this unique form.

Using spatial point pattern analysis, a method used in modern spatial ecological studies, we examine the distribution of Obamus on LV-FUN. Our analysis indicates that Obamus were distributed in strongly aggregated clusters although their edges were not touching, Three out of the four Obamus beds have extremely well developed and variable textured organic surfaces. However, the distribution of Obamus are not dictated by specific mat types. Intraspecies aggregation is the norm for modern marine invertebrates. There are many possible explanations for the significant aggregation of Obamus, including dispersal, spatially selective larval stages, or the distribution of mature microbial mat on the seafloor.