A researcher calls it "a decades-old mystery that has been the Holy Grail of paleontology": What, exactly, Dickinsonia was. It's one of a group of lifeforms called the Ediacaran biota, which the BBC describes as the "first complex multi-cellular organisms to appear on Earth." But for decades they've defied definitive classification, with scientists suggesting they could be everything from lichen to giant single-celled amoeba to "evolutionary dead-ends." Now, an answer: Dickinsonia is an animal that dates back 558 million years, making it the earliest confirmed one in the geological record. That conclusion comes thanks to fat, reports Phys.org. Ilya Bobrovskiy of Australian National University discovered a Dickinsonia fossil in 300-foot-high cliffs along the White Sea in northwest Russia, in a place so remote she reached it via helicopter.
The fossil was superbly preserved, so much so that its tissue had cholesterol molecules present in it. "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," says ANU professor Jochen Brocks, co-author of the paper on the discovery, which was published in Science. The Cambrian explosion that gave rise to modern animal groups didn't happen for another 20 million years or so. As for the oval Dickinsonia's appearance, the BBC describes it as possibly bearing "a superficial resemblance to a segmented jellyfish." National Geographic delves into the difficulty of studying Ediacarans, who had no shells or bones to leave behind and whose "squishy bodies have long since decayed." Read more on how the team overcame that here. (Read more discoveries stories.)