A recently published paper by researchers from the South Australian Museum and University of California demonstrates that Earth’s earliest complex life, previously thought to have become extinct with no descendants, has similarities with creatures living today.
Through twelve years of excavating fossil seafloors at the Nilpena heritage site, Professors James Gehling and Mary Droser have found that the Ediacaran fossils of South Australia’s Flinders Ranges are the first real evidence of animal biodiversity.
“Since Ediacarans include weird forms that are nothing like younger fossils or animals living today, some people believe that the Ediacara were a failed experiment in the evolution of plants and animals,” said Professor Gehling.
“However, our research has shown that marine animals and sea-weeds living in an extinct Adelaidean Ocean 800 to 500 million years ago were the ancestors of all modern marine animals.
“We know this because of the traces that these creatures have left behind in fossil seafloors.
“At Nilpena there is clear evidence that small and diverse animal groups were interacting as communities. We can see that they were growing, moving and feeding on the seafloor.
“For example, the Dickinsonia and Yorgia have left footprints of what are interpreted as resting traces – where these creatures remained still while they fed – before moving to the next site,” said Professor Gehling.
The apparent lack of shared characteristics between Ediacaran and Cambrian fossils – Ediacaran fossils were generally soft-bodied, whereas Cambrian fossils had hard structural elements – has also at times let to the belief that Ediacarans became extinct. However, this is challenged by the discovery in South Australia of a relatively new Ediacaran fossil, Coronacollina acula.
“The simplest early marine animals were sponges such as Coronacollina acula, which has needle like spicules that probably gave it structural support, in a manner resembling a much more refined sponge fossil, Choia, from the Cambrian period,” said Professor Gehling.
“The similarities are striking and show continuity in form from Ediacaran times to the Cambrian period.”
Further research into Ediacaran ecosystems, Ediacaran fossil structures and fossilisation processes has the potential of yielding ground-breaking understanding of the evolution of life.
“When we look at these fossil moments in the evolutionary history of the earliest groups of animals, we realise that there is a great deal more that Ediacaran fossils can tell us about life on Earth,” said Professor Gehling.
Professor James Gehling is a Senior Research Scientist at the South Australian Museum and an Affiliate Professor with the Sprigg Geobiology Centre at the University of Adelaide.
The advent of animals: The view from the Ediacaran by Mary L. Droser and James G. Gehling is available in a special feature of the Proceedings of the National Academy of Sciences (PNAS) on the Future of the Fossil Record.
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