Dickinsonia costata is an extinct organism from the Ediacaran period (635 - 543 Mya) and it is one of the first complex multi-cellular organisms to appear on Earth.
First discovered in 1947 by Reg Sprigg in the Flinders Ranges of South Australia, Dickinsonia is one of the most iconic creatures of the Ediacaran period - with a flattened, bilaterally segmented, disc shaped body that varied greatly in size from just a few millimetres to over one metre in length.
Recent molecular examination of organically preserved material has revealed that Dickinsonia produced cholesterol (Bobrovskiy et al, 2018) which is a characteristic of animal life, firmly placing Dickinsonia at the base of Kingdom Animalia.
Fossil remains also suggest that Dickinsonia may have been motile - able to slowly move around the ocean floor to feed on microbial mats. This is another important step in the evolution of complex life multi-cellular life - mobility. As no digestive tracts have been clearly identified it is thought that nutrients were absorbed directly through cell walls (osmosis).
How fossil remains of soft bodied organisms like Dickinsonia occurred in the first place has been a puzzle. It is now thought that prior to the advent of burrowing organisms an environment of overlaying microbial mats facilitated a type of "death masking" so that the impression of a soft bodied organism could be preserved (Gehling, 1999). This was no longer the case once burrowing organisms proliferated, churning up the seabed. It has also been speculated that the extinction of Dickinsonia and other Ediacaran biota was brought about by the evolution of these same burrowing creatures that effectively killed off the microbial mats that Ediacaran fauna fed upon. However the cause of the Ediacaran mass extinction is still unknown.
With thanks to Prof.Jim Gehling for feedback on anatomical detail.