STUDY: A Fossil Trove in China Provides a Rare Window Into a Mass Extinction Event That Happened More Than 500 Million Years Ago

Ace History Desk – Paleontologists have identified thousands of animal species that lived soon after the Cambrian explosion ended

When considering mass extinctions, people often think of the asteroid strike that wiped out all non-avian dinosaurs. But life on Earth has experienced many extinction events.

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Now, a trove of fossils found in southern China could shed light on the aftermath of one of these deadly episodes: the Sinsk event. Researchers describe thousands of the site’s remarkably preserved creatures, dated to around 512 million years old, in a study published January 28 in the journal Nature.

About 513.5 million years ago, the Sinsk mass extinction ended a period of animal evolution called the Cambrian explosion. But an incomplete fossil record, specifically of organisms with fast-decaying soft bodies, has made it difficult for paleontologists to study the Sinsk event’s impacts.

What spurred the Sinsk event?

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Researchers suspect the mass die-off occurred because of declining oxygen levels, but they’re not sure what led to the decrease. A study published in 2024 suggests that geologic activity increased the amount of greenhouse gases, such as carbon dioxide, in the atmosphere, which warmed it. Climate change then caused the circulation of ocean water to slow, resulting in oxygen-poor water.

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However, from 2021 to 2024, researchers conducted fieldwork at a phenomenal fossil deposit in the Renkupo quarry in China’s Hunan province. The site is “extraordinary,” study co-author Han Zeng, a paleontologist at the Chinese Academy of Sciences, tells Agence France-Presse.

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“We have collected over 50,000 fossil specimens from a single quarry that is 12 meters high, 30 meters long and 8 meters wide,” he says. “Many fossils show soft parts, including gills, guts, eyes and even nerves.”

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Zeng and his colleagues have officially classified 8,681 specimens, identifying 153 animal species among them—nearly 60 percent of which were previously unknown. The creatures lived in a marine ecosystem, which the researchers call the Huayuan biota.

Some of the recovered animals include sponges, molluscs, sea squirts, jellyfish relatives called cnidarians and arthropods, a group that includes modern spiders and scorpions. The roughly 30-inch-long arthropod Guanshancaris kunmingensis—which was an apex predator—was the largest of the fossilised animals identified so far, reports New Scientist’s James Woodford.

What’s more, “we found that the extinction mainly destroyed the shallow-water environment, and the deep-water environment at the edge of the continental shelf, where the Huayuan biota is situated, was less affected,” Zeng tells the outlet. 

Study co-author Maoyan Zhu, also a paleontologist at the Chinese Academy of Sciences, tells Reuters’ Will Dunham that this fossil deposit is the first to open a window into how the Sinsk event affected animals in deeper waters.

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The site’s diversity of creatures and level of preservation “vaults Huayuan into the top tier of Cambrian fossil sites,” says Joe Moysiuk, curator of paleontology and geology at the Manitoba Museum in Canada who was not involved in the study, to New Scientist.

Additionally, the team was surprised to spot animals that had previously been recovered only from the Burgess Shale biota, a famous Canadian fossil site dating back to the Middle Cambrian Epoch, around 520 million to 512 million years ago. “The best explanation of these shared taxa shall be that the larvae of early animals were capable of spreading by ocean currents since the early days of animals in the Cambrian,” Zeng tells Reuters.

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