A snapshot of life on a muddy sea bed 518 million years ago has been revealed at what is being described as a “stunning new locality” in central China. The Qingjiang fossil bed rivals the famous Burgess Shale formation in the Canadian Rocky Mountains, a site where sheets of rock were first split apart in 1909, revealing a wealth of exposed soft-bodied fossils.
The first detailed analysis of the Qingjiang biota, published in the journal Science, describes a diverse ecosystem of plants and animals from the early Cambrian.
The extraordinary find was the result of years of targeted explorations looking for Burgess Shale-type rock formations, and sheer luck.
On a particularly hot day in 2007, palaeontologist Xingliang Zhang and a group of students were scouting for promising rock formations in Hubei province in central China.
“We were walking along the road, trying to find some cool place for our lunch,” recalls Zhang. “We walked down to a riverbed and the rocks were washed by the water and you could clearly see the texture. I recognised that that kind of rock is the right rock we’re searching for. We started to split rocks and very soon found many fossils.”
That moment of scientific serendipity has yielded a stunning array of specimens from the dawn of complex life on Earth, entombed during an event more than half a billion years ago as known as the Cambrian explosion.
All animals alive today can trace their origins to the complex body forms that suddenly appeared in the fossil record during the period, which lasted from 541 to 485 million years ago.
The fossil record from that time is unique in having preserved animals with soft body parts. Few fossils with soft tissues exist from periods before or after the Cambrian period.
Dozens of Burgess Shale-type sites have been found around the world, but the Qingjiang site is unparalleled in the quality of specimens it contains.
“I never expected in my career to witness the discovery of a site as good as this one in the Cambrian,” says Allison Daley, a palaeontologist from the University of Lausanne in Switzerland who describes the “stunning new locality” in an accompanying commentary article.
“The quality of the fossils is outstanding,” she says.
Publication of the work has been eagerly anticipated. Zhang’s team has been giving its colleagues tantalising glimpses of what the Qingjiang rocks hold at scientific conferences over recent years.
John Paterson, a palaeontologist from the University of New England in Armidale, Australia, who works on Cambrian fossils, recalls a presentation at a 2016 meeting in the city of Adelaide.
“You could actually hear people gasping as [first author Dongjing Fu] put up different slides of these fossils,” he says.
Like Paterson, Daley had heard about the site at scientific conferences. But, she says, “to see the work of the paper, how thoroughly they’ve analysed the sediments, and the quality of the fossils, it really blew my mind.”
Unlike other formations from the Cambrian, the fossil-bearing layers at the Qingjiang site have not undergone metamorphosis in the millennia following their burial. Metamorphosis occurs when intense heat and pressure result in chemical changes in the fossilised bodies and their surrounds.
This “overprinting” of the original chemistry – as occurred in the Burgess Shale – limits what scientists can learn of the original ocean and sea floor chemistry of the captured ecosystem, says Paterson. That’s hasn’t happened at this new site.
An analysis of more than 4000 specimens from the original site at the Danshui River and nearby localities reveals that the ecosystem was diverse. More than half of the animals are completely new to science.
A remarkable 85% of the specimens are entirely soft-bodied animals, preserved in exquisite detail.
“I saw the photos, and you think ‘that is a jellyfish, no doubt about it, that’s a jellyfish, and that’s a sea anemone.’ It’s incredible to see these animals preserved,” says Daley.
Jellyfish, indeed, were particularly abundant at the site. Rare kinorhynchs, or “mud dragons”, sub-millimetre worm-like creatures usually undetectable to the naked eye in modern-day sediments, are also represented by new species, some up to four centimetres in length.
More than 30,000 specimens have been excavated from the Qingjiang site so far, says Zhang. The meticulous work of describing all of them is now underway.
“All these specimens need to be described, need to be worked on,” he says.
Daley expects the biota to shed light on some of the burning questions about how animals with different body forms evolved and spawned the complex tree of life we see today.
“At the base of the animal tree, there are still debates about exactly how things are related to each other,” says Daley.
That work could re-write the textbooks on animal evolution, says Paterson. “It’s going to be a case of ‘watch this space’,” he adds.
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