But what were they? Some looked like tall fronds; others, such as Dickinsonia, were flat mats. They were so unlike the animals, plants, and other organisms we know today that one scientist described them as “strange as life on another planet, but easier to reach.” Some paleontologists, including Dickinsonia’s original discoverer, classified them as animals, precursors to the more familiar forms that arose later, during the Cambrian explosion. Others have taken them for giant amoebalike protists, lichens, colonies of bacteria, or even a completely extinct kingdom of life.

Bobrovskiy recently came up with a new way of resolving these debates. While looking at Ediacaran fossils under a microscope, he noticed distinctive dark films. These were the unmistakable signs of organic compounds that had been left behind when their owners’ bodies had decayed. Large, complicated molecules such as DNA or proteins don’t survive long after an organism’s death, but smaller and more stable molecules can. If Bobrovskiy could recover them, he could look for distinctive chemical signatures that distinguish animals from bacteria and other kingdoms of life. “[My supervisor] Jochen [Brocks] said we could try it, but he was always sure that it was a stupid idea,” Bobrovskiy says. “Even I thought it would fail. But it didn’t.”

Bobrovskiy dug up eight new Dickinsonia fossils from Lyamtsa, a location on the edge of Russia’s White Sea. He used solvents to extract any ancient organic molecules from those specimens, and then identified all the chemicals in the extracts. He was looking for traces of one particular group: the steroids.

The word steroid is most commonly associated with performance-enhancing drugs, but it refers to a much broader class of chemicals found in the cells of all complex creatures, including animals, protists, and fungi. These steroids come in different varieties, and each is diagnostic of a different group of organisms.

For example, Bobrovskiy found that the clay and sandstone sediments around the Dickinsonia fossils were rich in stigmasteroids, which are indicative of green algae. By contrast, the steroids in the actual fossils were almost entirely cholesteroids. That ruled out the possibility that Dickinsonia was a lichen or a protist (since these contain very different blends of steroids) or a colony of bacteria (since these don’t produce steroids at all). Indeed, only one group of organisms produces cholesteroids to the exclusion of anything else: animals. Dickinsonia was one of us.

Bobrovskiy almost sounded disappointed when I talked to him about it. “I was hoping that it would be something stranger, but animal is the only possible interpretation,” he said.

“The question of whether the Ediacara biota was a prelude to complex, animal-dominated ecosystems or a failed evolutionary experiment is fundamental to our efforts to understand the emergence of biological complexity on our planet,” says Lidya Tarhan from Yale. Bobrovskiy’s study doesn’t fully settle that question—it doesn’t say if Dickinsonia was a forerunner to any recognizable animals, or part of a group that went extinct. But it does suggest that the animal kingdom has deeper roots than many scientists appreciate.