Filling in the Spaces: Spatial Point Pattern Analysis of Sessile Ediacaran Taxa From Nilpena Ediacara National Park, South Australia

The sharing of ecospace with organisms of the same or different species is one of the most fundamental properties of life. The excavation and conservation of nearly 40 bedding plans covered with in situ Ediacaran fossils at Nilpena Ediacara National Park in South Australia, allows for the application of spatial ecological techniques typically used on modern ecosystems to test hypotheses about spatial properties of Earth’s oldest animal communities. Using a combination of photogrammetry and spatial point pattern analysis, the spatial relationships of the sessile taxa Aspidella, Obamus, and Tribrachidium in the context of body size and abundance is presented here. Two Aspidella dominated beds, a Tribrachidium dominated bed and one Obamus populated bed from two of the four fossiliferous facies at Nilpena were examined for this study. Results reveal that Aspidella and Obamus are distributed into segregated clusters, while Tribrachidium are more spatially homogenous. The Aspidella clusters are heavily influenced by the taxon’s dominance on the beds and by environmental factors (surrounding taxa, taphonomy, etc.). Additionally, sized-based analysis reveals the potential for intraspecific competition amongst the Aspidella, while also fortifying a continuous reproduction hypothesis. Obamus show “hyper aggregation,” which is potentially a result of dispersal limitation. Finally, Tribrachidium spatial results support a seasonal reproductive method and passive suspension feeding strategy