Scientists have found what appears to be the earliest confirmed animal in the geological record.

The strange creature called Dickinsonia lived on Earth 558 million years ago, growing up to 1.4 metres in length, oval shaped with rib-like segments running along its body.

It was part of the Ediacara Biota that lived on Earth 20 million years prior to the 'Cambrian explosion' of modern animal life.

The Dickinsonia fossils could hold the key between the old world dominated by bacteria and the world of large animals that emerged 540 million years ago.

ANU researchers found a Dickinsonia fossil so well preserved in a remote area near the White Sea in the northwest of Russia that the tissue still contained molecules of cholesterol, a type of fat that is the hallmark of animal life.

“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 ANU’s Associate Professor Jochen Brocks.

“Scientists have been fighting for more than 75 years over what Dickinsonia and other bizarre fossils of the Ediacaran Biota were: giant single-celled amoeba, lichen, failed experiments of evolution or the earliest animals on Earth. 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.”

The team developed a new approach to study the fossil.

The challenge was to find Dickinsonia fossils that retained some organic matter.

“Most rocks containing these fossils such as those from the Ediacara Hills in Australia have endured a lot of heat, a lot of pressure, and then they were weathered after that - these are the rocks that palaeontologists studied for many decades, which explained why they were stuck on the question of Dickinsonia's true identity,” said researcher Ilya Bobrovskiy.

Mr Bobrovskiy extracted and analysed molecules from inside the Dickinsonia fossil found in ancient rocks in Russia to make the breakthrough discovery.

“I took a helicopter to reach this very remote part of the world - home to bears and mosquitoes - where I could find Dickinsonia fossils with organic matter still intact,” Mr Bobrovskiy said.

“These fossils were located in the middle of cliffs of the White Sea that are 60 to 100 metres high. 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.”

The full study is accessible here.