Fossil of earliest known animal discovered

Scientists have discovered an ancient fossil of the earliest animal on geological record -- a strange oval creature with rib like segments running along its body that lived on Earth 558 million years ago.

The animal called Dickinsonia, which grew up to 1.4 metres in length, was part of the Ediacara Biota that lived on Earth 20 million years prior to the 'Cambrian explosion' of modern animal life.

Researchers from Australian National University (ANU) found the 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 'Cambrian explosion' was when complex animals and other macroscopic organisms -- such as molluscs, worms, arthropods and sponges -- began to dominate the fossil record.

"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 Jochen Brocks from the ANU.

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

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, he said.

The team developed a new approach to study Dickinsonia fossils, which hold the key between the old world dominated by bacteria and the world of large animals that emerged 540 million years ago during the 'Cambrian explosion'.

"The problem that we had to overcome was finding Dickinsonia fossils that retained some organic matter," said Ilya Bobrovskiy, a PhD scholar at ANU.

"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," she said.