What was the earliest animal on Earth? Scientists have sought an answer for decades and have now identified Dickinsonia costata, an organism that lived 558 million years ago.

The earliest animal remains are represented by impressions preserved in rock rather than by fossilised body material, including those found in the Ediacara Hills of Australia.

One such impression was left by Dickinsonia, an organism discovered in the Ediacara Hills. It reached up to 1.4 metres in length, had an oval shape and a segmented body, and lived approximately 558 million years ago. This places it roughly 20 million years before the Cambrian Period, when the famous rapid diversification of animal life established body plans that persist today, including those of molluscs, worms, arthropods and sponges.

For 75 years, researchers attempted to determine what kind of organism Dickinsonia was: a giant single-celled amoeba, a lichen, an unusual animal, or perhaps an evolutionary lineage without living descendants.

The solution came from a region in north-western Russia near the White Sea. On the slope of a 60–100-metre-high cliff, Ilya Bobrovskiy, a researcher at the Australian National University (ANU), discovered an impression of Dickinsonia. Palaeontologists generally focus on the structure of these impressions, but Bobrovskiy also analysed molecules preserved within the fossil. He found that the impression of Dickinsonia contained cholesterol molecules. Cholesterol is a lipid characteristic of animals, supporting the identification of this organism as the oldest animal discovered to date, a long-sought finding in palaeontology.

These molecules could not be identified in fossils from the Ediacara region because those rocks had been subjected to high pressures and temperatures over the hundreds of millions of years between the organisms’ deaths and the discovery of their remains.

This is one of the most significant palaeontological discoveries of recent years. It demonstrates that animals were abundant millions of years earlier than previously thought, substantially changing our understanding of the history of life on Earth.

Sources: phys.org, Scientific American, Science Daily