AND NOW FOR SOMETHING COMPLETELY RANDOM: SPATIAL DISTRIBUTION OF DICKINSONIA ON THE EDIACARAN SEAFLOOR

The Ediacara biota are a suite of complex multicellular organisms living in a time before predation or bioturbation. At Nilpena Ediacara National Park (NENP), South Australia, a combination of preservation and excavation allows for the reconstruction of entire bedding plans revealing in situ Ediacaran communities. The third most abundant taxon at NENP is Dickinsonia costata, an ovoid to elliptical organism divided longitudinally into modules with a central midline that has been determined to be mobile with some degree of sensory organs. Four bedding surfaces (STC-I, STC-X, TB-ARB, TC-MM3) with abundant (i.e., more than 20 individuals) D. costata populations were examined using spatial point pattern analysis. Beds range in size from 19.7 to 9.0 m², with D. costata populations ranging from 22 to 192 individuals. Bedding surface STC-I has a population of D. costata consisting of individuals no larger than 3 cm in length, while the populations on TB-ARB, s STC-X and TC-MM3 have individuals ranging to over 10 cm. Additionally mat maturity and type vary by bedding surface.

Results show that all four populations are distributed randomly and their locations are independent of all other taxon on the surface. The results from beds STC-I differ from populations examined in the Central Urals, Russia where a juvenile population of Dickinsonia was determined to aggregate (spatially closer together then a random pattern). Additionally, the mat type and maturity had no effect on the distribution of NENP D. costata populations. These results show that at the scale of meters D. costata were not hampered by a heterogenetic seafloor, limited resources, and/or other taxa on a surface. Thus, D. costata were likely able to feed across the Ediacaran seafloor without spatial impediment.