Researchers say the fossils were made by an animal that existed more than 500 million years ago, before the Cambrian Period. The animal was soft and watery, and it may have looked something like a slug or jellyfish.
Scientists believe they have confirmed that some strange looking fossils were made by an animal, according to a paper released Thursday by the journal Science.
First discovered in 1947, the fossils date back more than 500 million years. They are oval in shape with internal lines, and look somewhat like a leaf imprint densely packed with veins.
Such fossils have been found in Russia and Australia and vary in size, with some as small as a fingernail and others measuring 1.22 meters long.
They have been a source of debate among scientists for decades but, after analyzing the contents of a fossil found off cliffs near the White Sea in northwestern Russia, researchers discovered molecules of cholesterol, a type of fat.
The discovery of the fat confirms that the creature, dubbed "Dickinsonia," is the Earth's earliest known animal, according to the paper.
'The Holy Grail of paleontology'
"Scientists have been fighting for more than 75 years" over the nature of these "bizarre fossils," said associate professor Jochen Brocks from the Australian National University Research School of Earth Sciences.
"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 creature was part of the Ediacara Biota that lived on Earth during a time when bacteria dominated, between 542-635 million years ago.
The Ediacaran Period came about 20 million years before modern animal life — a period known as the Cambrian explosion.
But scientists are still unsure what Dickinsonia actually looked like.
"We have no clue," Brocks told news agency AP. "We do know it was soft and flexible … Maybe like a slug, but less watery than a jellyfish," he added.
Previous research had also pointed in the direction of the fossils having being made by an animal.
In September 2017, British researchers said they were certain it was an animal, based on a study of multiple fossils. In 2015, another team of researchers concluded that it was a relatively advanced type of animal because of the way its body grew differently than plants or mushrooms.
law/rc (AFP, AP)