After the most severe known mass extinction in Earth’s history, living marine ecosystems could recover in just a million years, researchers report in the journal Science from February 10. This is millions of years earlier than previously thought. Evidence contained in a diverse treasure trove of pristine fossils discovered near the city of Guiyang in southern China may represent the first foundations of modern ocean ecosystems.
According to paleontologist Peter Rupnarin of the California Academy of Sciences in San Francisco, who was not involved in the study, the ocean was thought to have been dead for millions of years after this mass extinction. “Well, that’s not true. Ocean [був] very much alive.”
The Great Extinction, or Permian-Triassic mass extinction, occurred about 251.9 million years ago, at the end of the Permian period, after a series of powerful volcanic eruptions.
“The oceans have warmed significantly, and there is evidence of acidification, deoxygenation [що викликає широкі мертві зони], as well as poisoning,” says Rupnarin. “A lot of toxic elements like sulfur ended up in parts of the ocean.”
Life in the seas suffered. More than 80 percent of marine species have become extinct. Some researchers even suggest that entire trophic levels—castes in an ecosystem’s food web—may have disappeared.
Determining how long it took to fully recover from all this loss was difficult. In 2010, researchers studying the fossils of the Luoping biota in China suggested that complex marine ecosystems had fully recovered within 10 million years. Later, other fossil finds, such as the Paris biota in the western United States and the Chaohu biota in China, led scientists to suggest that marine ecosystems recovered in just 3 million years.
Then in 2015, a serendipitous discovery narrowed the gap again. Paleontologist Xu Dai, then a student at the China University of Geosciences in Wuhan, was studying Early Triassic rocks on a field trip near the city of Guiyang when he cracked a piece of black shale. In the rock, he discovered a surprisingly well-preserved fossil of what would later be identified as a primitive lobster.
The impeccable condition of the arthropod caused a series of return trips. From 2015 to 2019, Dye, now at the University of Burgundy in Dijon, France, and his colleagues discovered a bricolage of fossilized life: predatory fish as long as baseball bats. Ammonoids in twisted shells. Eel-shaped conodonts. Early shrimp. Sponges Bivalves Fossilized feces.
And the prizes kept coming. Both under and within the Guiyang biota, Dai and his colleagues discovered layers of volcanic ash. Analysis of the uranium and lead content of the ash indicated that the Guiyang biota contains fossils from about 250.7–250.8 million years ago. The dating was also confirmed by the types of fossils found and the analysis of different forms of carbon in the rocks.
Finding a medley of life from this era suggests that marine ecosystems recovered quickly after the Great Dying, within just 1 million years or so, Dye says.
Alternatively, it could mean that the extinction event failed to wipe out entire trophic levels, says paleontologist William Foster of the University of Hamburg in Germany, who was not involved in the study. “You have this ecologically stressed world, but some former marine ecosystems have survived.”
Despite this, it is clear that these ecosystems were resilient. Due to the movement of tectonic plates, the community preserved in the Guiyang biota was located in the tropics at the beginning of the Triassic. At the time, the sea surface temperature was nearly 35⁰ Celsius, and past research has shown that many organisms could migrate to escape the heat. But the discovery of the Guiyang biota challenges that, Foster said. Sea creatures “somehow tolerate it, they adapt.”
According to Dye, the fossils may be evidence that the roots of modern marine ecosystems took hold shortly after the Great Dying. “These groups are related to modern fishes, lobsters and shrimps, their ancestors,” he says. “The earliest time we can find seafood similar to today’s — [за часів] biota of Guiyang”.
But Roopnarine is skeptical. According to him, it remains to be found out exactly how Guiyang’s biota is related to modern ecosystems. The fossil assemblage may represent an ephemeral collective of life rather than a stable community, he adds, pointing out that ammonoids and conodonts became extinct.
Dai says further work will help resolve many of the questions raised about Guiyang’s biota. He and his colleagues plan to return to the field this summer for the first time since 2019. When asked if he would look at another lobster, he says, “Sure.”
