Scientists identify earliest known animal 558 mn years ago
22 Septembre, 2018, 05:10 | Auteur: Therese Cote
"The fossil fat now confirms Dickinsonia as the oldest known animal fossil, solving a decades-old mystery that has been the Holy Grail of palaeontology".
Dickinsonia belonged to a group of now-extinct life forms called the Ediacaran biota.
Previous samples of the animal were not as well preserved to keep organic matter from degrading.
The Cambrian Explosion, around 541 million years ago, was a period when a wide variety of animals burst onto the evolutionary scene.
A team of scientists, including from the Australian National University, have made the breakthrough discovery they're calling "the holy grail of paleontology", after finding molecules of fat in perfectly-preserved fossils mined from a desolate and remote corner of Russian Federation. Most of the Dickinsonia fossils we have are from the Ediacara Hills in Australia, and have endured a lot of heat, pressure and weathering, the researchers said, leaving no organic matter behind.
"The fossil fat molecules that we've found prove that animals were large and abundant 558 million years ago, millions of years earlier than previously thought", said Associate Professor Jochen Brocks from the ANU Research School of Earth Sciences in a statement. The fossil is said to be the "the key" linking the old world of bacteria and the new world of larger animals that came after the "Cambrian explosion" of life around 540 million years ago. Previously, the oldest macroscopic animal in the geological record was the mollusc-likeKimberella from 555 million years ago.
Dickinsonia is part of the Ediacaran biota, a class that includes other soft-bodied organisms similar to jellyfish, sea anemones, or worms. Scientists have typically studied the creatures by physically analyzing their ancient imprints.
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Bobrovskiy found the fossils in the middle of the White Sea cliffs, approximately 200 to 330 feet high.
Bobrovskiy and his colleagues extracted molecules known as sterane hydrocarbons (Rincon notes that traces of these molecular structures can linger for millions of years) from the fossils and found they contained cholesterol levels of up to 93 percent, as opposed to the 11 percent seen in surrounding sediment.
"I had to hang over the edge of a cliff on ropes and dig out huge blocks of sandstone, throw them down, wash the sandstone and repeat this process until I found the fossils I was after", he added.
Bobrovskiy then developed a special technique to test the Dickinsonia remnants for cholesterol. Finding this particular specimen was a grueling task, said Ilya Bobrovskiy, co-author of the paper and a PhD student at ANU.
As soon as Bobrovskiy showed the findings to Brocks, he immediately realized what he saw, noting they were a game changer and he "immediately saw the significance". "But applying biomarkers removes a large part of this uncertainty".
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