Chinese fossils force major rethink of 'Great Dying' rebound
Long before the first dinosaurs roamed the Earth - and then suddenly did not - there was another, far bigger mass extinction.
The "Great Dying" 252 million years ago wiped out massive swathes of life on Earth, including more than 80 per cent of marine species, in what scientists call the Permian-Triassic mass extinction.
It is generally believed that the event was caused by intense global warming that heated the oceans, causing the metabolisms of sea creatures to speed up. Eventually, there was not enough oxygen for ocean animals to breathe.
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Despite the scope of the eradication, life eventually rebounded during the following Early Triassic period.
Scientists have long been trying to trace the recovery of marine life during this crucial time when evolutionary changes exploded, eventually laying the foundation for the ecosystems that dominate our oceans today. The problem, until recently, has been a lack of fossils.
"The lobster drew our attention," said Dai Xu, a palaeontologist from the school of Earth sciences at the China University of Geosciences, and an author of a new study that resets the time when marine life recovered from the extinction event.
Dai is part of an international team of researchers who have spent eight years at a field known as the Guiyang Biota, the remnants of an ancient seabed unearthed near the capital of the Guizhou province in southwestern China.
The area is rich in fossils of diverse marine ecosystems that feature the earliest records of lobsters and shrimp, and even an early fish called a coelacanth - a living fossil that still exist today.
In 2015, researchers unearthed pieces of an ancient lobster fossil in the area, a rare find among early Triassic fossils, which led to other discoveries that helped them piece together the ecosystem puzzle. Fossils of the lobsters and shrimps predated the previous oldest reports by 1.5 million years, they found.
"We carried on with field work around Guiyang for years to accumulate [fossil records] and gradually unfolded a tip of the iceberg in the Guiyang Biota," said Dai, who added they will continue excavating around the area.
The picture that emerged would reset long-held assumptions about the recovery of life after the cataclysm of the Great Dying.
From their extensive fossil collection uncovered in the area, the scientists concluded that marine life on Earth recovered 1 million years after the Great Dying - much earlier than previously thought.
The researchers from Canada, China, France, Switzerland and the United States published their findings in the peer-reviewed journal Science on Friday.
The Guiyang Biota, which is near the equator, indicates "a rapid rise of modern-type marine ecosystems after the Permian-Triassic mass extinction, despite global sea-surface temperatures remaining high", the researchers said in the article.
Until recently, it was thought that the full re-establishment of complex marine ecosystems had not occurred until around 10 million years after the mass extinction, as represented by fossils from the Luoping Biota in the neighbouring province of Yunnan.
The team said the Guiyang Biota contained representatives of all levels in a food web - from primary producers, such as algae, to primary consumers like foraminifers (microscopic single-celled organisms) and sponges, and mesoconsumers such as bivalves (shellfish) and brachiopods.
There are also predatory invertebrates, such as ammonoids and decapods (including shrimp and lobsters), as well as predatory fish and reptiles.
Lead author Song Haijun, a professor of geobiology at the China University of Geosciences, said international collaboration was key for the extensive analysis, from age dating to identifying animals.
"We were fortunate to have found zircon from volcanic ash in the area. The mineral is ideal for precise age determination. We worked with the world's top dating scientists to report on the age of the biota," he said, referring to peers in Canada and Switzerland.
The Chinese palaeontologists also worked with researchers from other Chinese institutes, as well as France and the US, who specialise in different animal groups, such as fish, shrimp and invertebrates, to identify the specimens, some of which are extinct.
This article originally appeared on the South China Morning Post (SCMP).
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