It was oval and flat with a kind of central dorsal, measured several tens of centimeters in length and lived at the bottom of the oceans, without mouth, intestines or anus, half a billion years ago.

Thousands of Dickinsonia fossils have been found for 75 years on the planet, but its belonging to the animal kingdom – one of the great kingdoms of life, with plants, fungi … – was debated in the scientific community. Was it a lichen? An amoeba? An ancient extinct kingdom?

Researchers at the Australian National University (ANU) have provided what they believe is decisive evidence that the creature was indeed one of the earliest animals to have lived, or at least the oldest ever confirmed. They described their method Thursday in the prestigious journal Science.

Until now, paleontologists studied the morphology of a fossil to deduce its type.

Ilya Bobrovskiy, a doctoral student at the Australian university, instead analyzed remnants of molecules recovered from fossils found on a cliff in northwest Russia, in the White Sea region.

Another team had concluded in 2015 that they were animals, relatively advanced, because of the way their bodies grew, unlike plants or fungi.

But it is the very nature of scientific research to confirm a hypothesis over the years, multiple times and using different methods.

“The paper overstates the existing controversy a bit,” says paleobiologist Doug Erwin at the Smithsonian Institute in Washington. But, he says, “it’s a good paper.”

“This is the first time biological markers have been used for Ediacaran fossils,” he notes.

The Ediacaran is the period (-635 to -542 million years) preceding the era that marks, according to scientists, the rapid appearance of all major groups of animals on Earth: the famous Cambrian event, relatively short from a geological perspective, between 30 and 40 million years.

This is precisely why the confirmation that animals have existed before is so important.

“For a long time, there were questions about whether the event was real, or whether we had failed to find older fossils,” says David Gold, a geobiologist at the University of California-Davis, and one of the authors of the 2015 study.

“This paper provides another very good piece of evidence that animals are much older than the Cambrian,” he adds.

Dickinsonia-like species would therefore be “the ancestor of many of today’s animal life forms,” he continues. This has not yet been verified, but he suggests that worms and insects may be descended from them.

The work published Thursday also marks a kind of “renaissance” in paleontology, with the use of tools that make it possible to find organic compounds that are hundreds of millions of years old.

Under the right conditions, scientists can now find proteins or pigments to identify the color of dinosaurs, says David Gold. Or, in this case, cholesterol, a carbon-based molecule.

Proving that Dickinsonia was an animal does not mark the end of the mystery. We still don’t know how it fed (without a mouth) or reproduced.

Above all, statistical calculations on DNA suggest that the animal kingdom dates back 720 million years. This leaves a gap of some 160 million years until the appearance of this flat, oval creature. Visit our website HERE