Sask. researchers help crack mystery 518 million years in the making

A fossilized worm found in the Chengjiang Biota. (Xiaoya Ma)

A new paper co-authored by University of Saskatchewan researchers shows the creatures responsible for one of the world's oldest and most complete fossil records lived more turbulent lives than previously thought.

The group of fossils — known as the Chengjiang Biota — deposited in Yunnan, China is 518 million years old.

The fossils are considered "the most complete snapshot of Earth's initial diversification, the Cambrian Explosion," says the paper, recently published in Nature Communications.

The marine fossils provide a glimpse into a time when life on Earth was undergoing dramatic changes.

"What we have here is sort of a snapshot of those really diverse communities that were evolving in shallow marine environments, around 520 million years ago," University of Saskatchewan geology professor Luis Buatois said in a phone interview.

Buatois is one of the paper's co-authors.

"We can call them worms in general, then there is a wide variety of arthropods, including trilobites, that were extremely common in what we call the Early Palaeozoic," he said.

"Even some of the earliest vertebrates were there; so what we are talking about here is what we call the Cambrian Explosion — which is the rapid appearance of the basic body parts of most animals."

While the fossils themselves have been extensively studied, the researchers focused on the environment where the creatures lived, previously believed to be a relatively stable, deep-water environment.

However, the researchers found this was far from the case.

By analyzing a core sample from the area, the research team found the animals were instead swept deep into the ocean from a river delta — a more challenging, unpredictable habitat, according to Buatois.

"They had to be able to survive there and that's kind of a big departure from previous ideas," Buatois said.

"The animals have to live with a series of stress factors, like for example, very rapid sedimentation, discharges of freshwater, or water turbidity."

The research team's findings offer fresh insight into the lives of animals that were entombed long before dinosaurs ever walked the Earth.

"When you are working with fossils, you need to first understand where they are preserved and then you have to evaluate if they have been transported or not," Buatois said.

"It seems these animals that we have always thought were adapted to a very stable low-energy environment — they were actually living closer to the shoreline."

The international team responsible for the paper also included researchers from Yunnan University, the University of Exeter, the Chinese Academy of Sciences, the University of Lausanne, and the University of Leicester.

By applying the team's methods, Buatois said long-held notions about other fossil sites could be upended as well.

"I don't think that we will end up reinterpreting everything as shallower water, but the picture that is emerging is that these sort of (animals) were actually living in a wide variety of environments."