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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.

Tribrachidium is a monospecific genus of the Ediacara biota that is found globally. In the Flinders Ranges of South Australia, the spatial distribution of Tribrachidium across the seafloor is best described as patchy. Although Tribrachidium is the dominant fossil on two of the twenty-six beds currently excavated and is present in large numbers on another, the genus most commonly occurs as no more than a handful of specimens on a bed. Tribrachidium size frequency distributions of each of the three beds with more than 5 specimens are all statistically distinguishable from one another. Additionally, the size range on any given bed is smaller than the overall size range observed for the genus. These patterns suggest that these organisms lived in populations composed of cohorts. The beds with numerous Tribrachidium come from different facies and are characterized by the presence of dissimilar mixes of taxa and textured organic surfaces, indicating that Tribrachidium was a generalist, able to adapt to a variety environments. Uniquely, the base or internal structure of Tribrachidium is also found preserved in both positive and negative relief as a sequence of concentric ridges on beds where Tribrachidium is the dominant genus. The most parsimonious explanation for the presence of these concentric ridge fossils is that they are the fossilized form of a Tribrachidium preserved when the organism was buried upside-down, flipped over, or partially decayed prior to burial.