Fat Molecules Confirm Mysterious Fossil Was an Early Animal, Rewriting the Origins of Animal Life

For more than seven decades, scientists have debated the true nature of Dickinsonia, a strange, quilted-looking fossil dating back 558 million years. Now, groundbreaking molecular research has definitively placed it within the animal kingdom, identifying it as Earth’s oldest known animal.

The study, published in Science and led by researchers at the Australian National University (ANU), found traces of cholesterol-like fat molecules in the fossilized remains—biochemical evidence that confirms Dickinsonia was, indeed, an animal and not a lichen, amoeba, or some other non-animal lifeform.

A Fossil That Stumped Scientists for 75 Years

Discovered in 1947 on cliffs near the White Sea in Russia, Dickinsonia belongs to a group of mysterious life forms known as the Ediacaran Biota, which lived on Earth between 635 and 541 million years ago—before the Cambrian explosion, the period traditionally considered the dawn of modern animal life.

For decades, Dickinsonia defied classification. Its ribbed, oval-shaped body had no mouth, gut, or clear signs of organs. Hypotheses about its nature included:

• A single-celled giant amoeba

• A fungus or lichen

• A failed evolutionary experiment

• Or a primitive animal ancestor

Molecular Clues Reveal Animal Identity

The scientific breakthrough came from chemical analysis. The research team extracted molecular fossils—traces of ancient fat molecules—from Dickinsonia samples preserved in rocks over half a billion years old.

“The fossil fat molecules that we’ve found prove that animals were large and abundant millions of years earlier than we previously thought,” said Jochen Brocks, ANU professor and co-author of the study.

These fat molecules, specifically cholesterol, are hallmarks of animal tissue, definitively ruling out other forms of life such as algae or fungi.

Implications for the Tree of Life

The findings push back the timeline for complex animal life on Earth by at least 20 million years—well before the Cambrian explosion, which has long been thought to mark the beginning of animal evolution.

It also lends weight to the idea that the Ediacaran period hosted a rich array of complex multicellular life, much of which remains poorly understood due to the soft-bodied nature of its fossils.

“Scientists have been fighting for more than 75 years over what Dickinsonia and other bizarre fossils of the Ediacaran Biota were,” said Brocks. “This study settles the debate.”

What Was Dickinsonia?

Though Dickinsonia remains enigmatic in many ways, its identification as an animal provides key evolutionary context:

• Lived: ~558 million years ago during the late Ediacaran period

• Size: Ranged from a few millimeters to over a meter long

• Shape: Oval body with symmetrical rib-like segments

• Lifestyle: Likely absorbed nutrients directly through its body while living on the seafloor

Its body plan is vastly different from modern animals, underscoring the diversity of evolutionary experimentation in Earth’s early biological history.