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Dickinsonia lived 558 million years ago in the ocean.

Dickinsonia lived 558 million years ago in the ocean. Image: Nature


The Inertia

In the late 1940s, scientists discovered the fossils of a weird, flat thing that looked like a cross between a pancake and a mushroom. Named Dickinsonia, they were in the oceans some 558 million years ago, and they were prolific. Now, nearly 70 years after their discovery, researchers have released a study that could change the way we believe life as we know it came into existence.

The Dickinsonia group was one of the most common residents in the ocean, but there was something odd about them—they were far larger than nearly everything else on Earth at the time. While most things grew to be at most just a few millimeters, fossilized Dickinsonia were found that measured nearly five feet. Scientists have been arguing about what, exactly, explains this strange size difference. According to Nature, they’ve “debated whether Dickinsonia were primitive animals, giant single-celled organisms called protists, bacterial colonies, or something else entirely” basically since they found them.

The Dickinsonia’s size has baffled scientists since its discovery. If you remember your high school biology class, you may be familiar with a time called the “Cambrian Explosion.” It was a period where basically everything on earth became plus-sized in a relatively short amount of time. Most of the major groups of animals we know today started, in some form or another, during that time. So why were scientists baffled about the size of the Dickinsonia group? Well, because they lived millions and millions of years before the Cambrian Explosion, which, even if they weren’t actually living animals, would be strange.

But the latest study, released on September 1 in Science, has answered the questions by doing something a little different. Instead of looking at the physical characteristics of the Dickinsonia, they analyzed chemical biomarkers that are almost impossible to find. See, for these biomarkers to exist, a creature needs to basically be mummified—researchers need to find preserved fat molecules called sterols. Normally, after millions of years, sterols are long gone, but in one particular place on the banks of Russia’s White Sea, an inlet of the Barents Sea, researchers were pleasantly surprised when they found a whole bunch of fossils stuck in a fossilized layer of algae. “It’s just incredibly lucky,” said Jochen Brocks, a paleo-biogeochemist at the Australian National University in Canberra. “They are, in principle, mummified Dickinsonians.”

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When the team looked at the biomarkers, they half expected to find that the Dickinsonia weren’t animals at all—the timeline, after all, is a few million years off. But what they found was that they were indeed animals that lived 17 million years before the Cambrian explosion. The finding led Nature to call the Dickinsonia the “world’s first animal,” which is a pretty heady title.

Of course, there was already evidence that the Dickinsonia was an animal, but not enough to say definitively. Fossil record indicated that they moved around and grew at a rate that’s relatively the same as we see today. The definitive finding throws a bit of a wrench in the history books bringing into question the whole Cambrian/Precambrian transition, which, as I said, is a bit of a starting point for life as we know it.