How we came to be: Scientists get first look at the evolution of early complex animals - AP News

How we came to be: Scientists get first look at the evolution of early complex animals

A massive fossil discovery in southwest China has shifted our understanding of when complex animals first appeared on Earth. Researchers from Oxford University and Yunnan University found that many animal groups evolved much earlier than previously believed, moving the timeline back by at least four million years.

This November 2023 photo provided by Gaorong Li shows a Haootia-like fossil at Yunnan University in Kunming, China. (Gaorong Li via AP)

WASHINGTON (AP) — Newly discovered fossils have given scientists their first real glimpse of when Earth made a crucial transition from plants and unrecognizably simple animals to the complex creatures that took over the world and would eventually lead to us.

And it happened millions of years earlier than researchers thought.

More than 700 fossils found in southwestern China’s Yunnan province offer a window into life from 539 million years ago, during the waning end of the Ediacaran period, a time of simple but strange animals that lived two-dimensionally in the oceans, never going up or down, researchers said.

But a study in Thursday’s journal Science said many of the fossils in this trove are remnants of more complex animals that lived three-dimensional lives, traveling up through the water and eating. Those are traits that had been thought to only spring to life at least 4 million years later in the Cambrian period, during what was called the Cambrian explosion of complex and recognizable animal life.

“This really is the first window we have into how basically the modern animal-dominated biosphere was formed and developed and came through this weird Ediacaran transitional interlude,” said co-author and paleontologist Frankie Dunn of the Museum of Natural History at Oxford University. “We go from a two-dimensional world, and within the geological blink of an eye, animals have diversified. They’re everywhere. They’re doing everything, and they’re changing biogeochemical cycles. They’ve changed the world.”

The new finds were a short distance from a United Nations Chengjiang world natural heritage site for other fossils in an exposure along a roadside that’s not glamorous, but has different layers “where you can literally walk through time, geological time, in a landscape,” Dunn said. And one of those areas provides a “snapshot” where evolution brings forces together.

Complex animals with symmetry developed

In that spot, Dunn said, the group of fossils includes both bizarre examples of life that existed in earlier periods and disappeared, along with early examples of organisms that would evolve into modern animals. What’s important in those more modern animals are that their bodies are mostly the same on the left and right.

Nearly all of the animal life on Earth now have similar features on left and right sides, as well as a head and an anus. Before the fossils discovered in China, scientists saw traces of this symmetric body type in fossil tracks, but not the critters themselves.

“Now we know what’s making them because we have those fossils for the first time,” said study co-author Ross Anderson, also of Oxford’s Museum of Natural History.

Help in settling ‘rocks versus clocks’ debate

Until now, there was a conflict in the field of paleontology. Genetic analysis of how fast traits mutated and evolved suggested that humans and starfish had their earliest common ancestor in the Ediacaran period, but the fossils or rocks weren’t there to show it happening, Dunn said. It was called a debate of “rocks versus clocks,” she said.

“What our new fossil site tells us is that actually perhaps the rocks and the clocks are in closer agreement than we thought,” Dunn said.