The oldest known animal in history has been discovered thanks to some well-preserved animal fat that’s been sitting in northwest Russia for the past 558 million years. The find expands the confirmed existence of animals by three million years.
The ancient animal is a Dickinsonia, which looks more like a creature from a sci-fi movie than something you’d expect to run into on Earth. Dickinsonia were oval-shaped creatures spread flat like pancakes that could grow up to four and a half feet long. Previously, the oldest macroscopic animal in the geological record was the mollusc-like Kimberella from 555 million years ago.
We already knew that Dickinsonia existed because of fossil imprints that show the animals’ eerily symmetrical, rib-like segments all over their bodies. Many of these fossils are found in southern Australia. But Ilya Bobrovskiy, a PhD student at Australian National University, had to travel to a cold, remote area near the White Sea to find ones that still had preserved fat.
“These fossils were located in the middle of cliffs of the White Sea that are [195 to 330 feet] high,” Bobrovskiy said in a university press release. “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.”
Before his discovery, it wasn’t clear that Dickinsonia were animals—i.e., that they belonged to Animalia, the same biological kingdom as humans. Dickinsonia are a type of Ediacaran biota, a group of organisms that emerged during the Ediacaran Period between 635 million and 541 million years ago. These organisms predated the “Cambrian explosion” of animal life over the next nine million years.
“Scientists have been fighting for more than 75 years over what Dickinsonia and other bizarre fossils of the Edi[a]caran Biota were: giant single-celled amoeba, lichen, failed experiments of evolution or the earliest animals on Earth,” said Jochen Brocks, a lead senior researcher at Australian National University, in the press release.
The Dickinsonia fossil tissue Bobrovskiy found contains cholesterol molecules; and because this type of fat is present in all animal tissues, it settles the debate. “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,” Brocks continued.
Bobrovskiy and Brocks’ collaborated with scientists from the Russian Academy of Sciences in Moscow; the Max Planck Institute for Biogeochemistry in Jena, Germany; and the University of Bremen in Bremen, Germany. They published their results in the journal Science.
“However alien they looked,” the authors write, the discovery of large Dickinsonia animals “reveals that the appearance of the Ediacara biota in the fossil record is not an independent experiment in large body size but indeed a prelude to the Cambrian explosion of animal life.”