The first fossils of animals are identified

Scientists have identified the first known animal in the geological archive.

It's a 558-million-year-old oval-shaped creature that could have a superficial resemblance to a segmented jellyfish.

The researchers found specimens of the creature, known as Dickinsoniawhich was so well preserved that they still contained cholesterol molecules.

This fat is a hallmark of animal life, reports the team in the journal Science.

Dickinsonia belongs to a group of life forms known as Ediacaran biota. They were the first complex multicellular organisms to appear on Earth.

But they were extremely difficult to categorize and their position on the tree of life was one of the biggest mysteries of paleontology.

Different teams of scientists have variously classified them as lichens, fungi, protozoa, evolutionary impasses and even as intermediate stage between plants and animals.

The new analysis of a specimen found in northwestern Russia Dickinsonia firmly in the animal kingdom.

"The fossil fat molecules we found prove that animals were large and abundant 558 million years ago, millions of years earlier than expected," said coauthor Jochen Brocks. , Associate Professor at the Australian National University (ANU). Canberra.

"Scientists have been fighting for over 75 years on what Dickinsonia and other weird fossils of Ediacaran biota were, "he explained, adding," 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. "

The Ediacaran biota appeared about 600 million years ago and flourished for tens of millions of years before the event called the Cambrian Explosion.

This massive diversification of life occurred about 541 million years ago; it is at this point that most large groups of animals appear in the fossil record.

The Ediacaran species disappears largely when the Cambrian explosion occurs. As such, they overlap an old age when the Earth was dominated by bacteria and an age of later domination by animals.

Most of the multicellular life leaves behind stable molecules called sterane hydrocarbons that can be kept in sediments for millions of years. The molecular structures and abundances of these compounds may be specific to particular types of organisms.

Ilya Bobrovskiy, a member of the ANU team, extracted and analyzed molecules from inside the fossil.

He found that Dickinsonia the fossils contained very high levels of cholesterol molecules – up to 93% – compared to surrounding sediments, where levels were about 11%.

In addition, fossils did not have the types of stable molecules that are sometimes left behind by fungi.

"The problem we had to overcome was to find Dickinsonia fossils that have preserved organic matter, "said Ilya Bobrovskiy.

"Most of the rocks containing these fossils, such as those in the Ediacara Hills in Australia, have been subjected to a lot of heat, a lot of pressure and they have been altered – the rocks that paleontologists have studied for decades, which is why why they were stuck on the question of Dickinsoniathe true identity. "

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