Dickinsonia costata is an extinct organism from the Ediacaran period (635 mya - 543 mya) and it is one of the first complex multi-cellular organisms to appear on Earth. It is also one of the most distinctive creatures of this period with its flattened, bilaterally segmented, disc shaped body.
Dickinsonia was first discovered in 1947 by Reg Sprigg in the Flinders Ranges of South Australia but has since been found around the world. It varied greatly in size from a few millimetres up to one metre in length.
Although Ediacaran organisms are clearly earlier, simpler lifeforms when compared to later Cambrian organisms, it has been hard for science to describe any clear affinities or direct connections between the two periods. 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. 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 the Ediacaran fauna fed upon. However the cause of any large scale Ediacaran extinction is still being debated.
With thanks to Prof.Jim Gehling for feedback on anatomical detail.