A 558 milion-year-old fossil has been identified as the world's oldest known animal, according to scientists.
Researchers, who published their findings in the journal Science on Friday, were able to extract cholesterol fat — a hallmark of animal life — from a particularly well-preserved fossil of a creature known as Dickinsonia. It was found near the White Sea in the northwest of Russia.
The oval-shaped creature, which had rib-like segments running along its body and grew up to be to 1.4 metres in length, belongs to a group of organisms known as the Ediacaran biota which lived on Earth from 635 to 540 millions years ago.
These particular life forms had until now evaded classification as scientists were stumped over their place in the evolutionary tree.
But the latest discovery places them firmly within the animal kingdom and dates the presence of animals of Earth 20 million years earlier than previously thought.
"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," lead senior researcher, Jochen Brocks, from the Australian National University said in a statement.
"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 evoution 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," he added.