The "fat" traces confirm that the strange fossils were the first animals

Washington (AFP) – A strange fossil that looks a bit like a giant leaf or coffee-sized footprint has intrigued scientists for decades.

Thousands of fossils have been discovered over the last seven decades, revealing that it lived on the bottom of the oceans, without mouth, intestines or anus, half a billion years ago.

Was it a mossy plant? A giant unicellular amoeba? A failed experiment in evolution? Or the first animal on Earth?

After digging one of these fossils on a cliff in Russia and analyzing its contents, researchers discovered molecules of cholesterol, a type of fat.

This confirms that the creature, known as Dickinsonia, is the earliest known animal on Earth, the journal said Thursday in the journal Science.

"Scientists have been fighting for over 75 years" about the nature of these "weird fossils," said Associate Professor Jochen Brocks of the Australian National School of Earth Sciences Research.

"The fossil fat now confirms Dickinsonia as the oldest known animal fossil, solving a decades-old mystery that has been the holy grail of paleontology."

– Cliff edge –

Dickinsonia contained vein-like segments along the length of his oval shaped body, varying in size and up to 4.4 feet (1.4 meters).

The analysis showed that animals were plentiful 558 million years ago, millions of years earlier than expected, according to Brocks.

The creature was part of the Ediacara biota that lived on Earth at a time when bacteria reigned, 542-635 million years ago.

The Edicarian period was about 20 million years before the emergence of modern animal life – a period known as the Cambrian explosion.

"The question was, is it real – is it an event that has occurred in the history of the Earth – or have we not found the oldest fossils?" David Gold, a geobiologist and assistant professor at the University of California, told AFP.

"This article is another very good source of evidence to support the idea that it is actually an animal, and that the animals are much older than the Cambrian."

Dickinsonia could be an ancestor of "many forms of animal life today," including worms and insects, added Gold, which was not part of the current study.

Scientists have struggled to find Dickinsonia fossils that still contain organic matter.

Many known fossils were found in Australia and had been exposed to too many elements over millions of years.

The fossil of the current study comes from cliffs located near the White Sea in northwest Russia.

"I took a helicopter to reach this very remote region of the world – where bears and mosquitoes live – where I could find Dickinsonia fossils whose organic matter was still intact," said Ilya Bobrovskiy, researcher at l & # 39; ANU.

"These fossils were located in the middle of the White Sea cliffs, which are between 60 and 100 meters high, I had to hang ropes from large blocks of sandstone, throw them, wash the sandstone and repeat this process until they reached the end. to find the fossils I was looking for. "

– Ancestor of the worms? –

Other researchers have already claimed to have solved the mystery of the animal.

In September 2017, British researchers said they were certain that it was an animal, according to a study of several fossils.

Another team of researchers, including Gold, also concluded in 2015 that it was a relatively advanced type of animal because of the way its body grew differently from the plants. and mushrooms.

Although the case is not fully resolved, paleobiologist Doug Erwin said, "I think the consensus of the majority of people who have been working on these fossils for a decade or so is animal related. "

The Australian team "is trying to make more controversy than I think it is, and paper is still a good article," he told AFP.

"This is a new line of evidence that is certainly welcome."

In this sense, the report represents the first time that biomarkers have been used to determine that a fossil of the Edicarian period is an animal instead of something else.

"This is part of a renaissance in the field of paleontology," Gold said.

"As we discover that our tools and technologies are improving, we are seeing that there are actually all kinds of organic matter – proteins, fats, different carbon compounds – things that we believe could not survive. such a long period of time, "he added.

"Because of this, we can find things like preserved pigments to see the colors of the dinosaurs, or in this case, the cholesterol content of a fossil 500 million years old."