Some 635 million years ago, as the Earth shook off massive shrouds of glacial ice, an alien world blossomed on the ocean floors.

No complex animals prowled the seas of the Ediacaran Period. Instead, the depths held microbial mats and strange, frond-like creatures that resembled nothing alive today. Paleontologists have suggested that this was a sort of Garden of Eden, a simple ecosystem wiped away by the more vibrant fauna of the following Cambrian Period.

But recent research is complicating this view, suggesting that Ediacaran ecosystems were more complex than previously thought. Fossils also hint at the beginnings of a massive shift: scavenging that later evolved into predation.

“It’s the beginning of a major change in the ecosystem of the Earth, an irrevocable change,” said Mary Droser, a paleobiologist at the University of California, Riverside. “The ability to eat another animal is a big deal, and is a major ecological and biological innovation.”