The earliest known animal to exist on Earth did so 558 million years ago – millions of years earlier than thought.

A study published in the journal Science confirms that a mysterious and much debated fossil species, called Dicksonia, was unequivocally an animal, and not an ancient lichen or giant amoeba as previous analyses have suggested.

The discovery – which researchers have dubbed “the Holy Grail of palaeontology” – was made after Ilya Bobrovskiy from the Australian National University discovered an extremely well preserved Dicksonia fossil near the White Sea in northwest Russia.

Dicksonia date to the Ediacaran period, which predates the so-called “Cambrian explosion” by 20 million years. It was during the Cambrian period that complex animals – such as worms and molluscs – were thought to have emerged.{%recommended 7313%}

The new analysis, however, shows that bona fide animals, and not just plants, fungi and unicellular bacteria, were already well established.

Dicksonia was by no means a tiny creature. The specimen discovered by Bobrovskiy and his colleagues was up to 1.4 metres in length. Flattened by the fossilisation process, it presents as roughly oval, with a large number of fine ridges radiating either side of a clearly visible centre-line.

The species has been known for around 75 years. Most examples, however, have been discovered in the Australia fossil beds known as the Ediacara Hills (from which the period derives its name) and were poorly preserved.

Bobrovskiy located his example in a very different part of the world – halfway up a 100 metre-high cliff above the White Sea.

The fossil was exquisitely preserved, so much so that it still contained fat molecules. The researchers were able to isolate these and identify them conclusively as cholesterol – a fat type found only in animals.

It is a finding that will rewrite the ancient history of 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,” explains co-author Jochen 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.”