Shrimp and worms among the first animals to recover from the greatest mass extinction

Researchers studying ancient seabed tombs and trails have found that benthic animals were among the first to return after the late Permian mass extinction.

In a new study, published today in the journal Researchers progressScientists from China, the United States and the United Kingdom reveal how marine life recovered after the event, which killed more than 90% of the Earth’s species, from their observations of fossil tracks.

Life was destroyed by the mass extinction at the end of Perm 252 million years ago, and the restoration of life on Earth took millions of years for biodiversity to return to pre-war levels. But by exploring the paths and caves on the seabed in southern China, the international team was able to put together the revival of marine life by identifying what animal activity took place and when.

Professor Michael Benton of the School of Earth Sciences at the University of Bristol, a contributor to the new paper, said: “The late Permian mass extinction and early Triassic restoration of life is very well documented throughout southern China.

“We were able to study trace fossils from 26 sections across the entire series of events representing a crucial seven million years, showing details of 400 test points, we finally reconstructed the recovery stages of all animals, including benthos, nectons, as well as the soft animals that dig themselves into the sea. “

Dr. Xueqian Feng from China University of Geosciences in Wuhan led the study, focusing on ancient caves and paths. He explained: “Traces of fossils such as paths and caves document mainly soft animals in the sea. Most of these soft animals had no or no skeletons.

“There are amazing sites in southern China where we find a large number of beautifully preserved track fossils, and the details can show engineering behavior in the fauna ecosystem as well as their feedback effects on skeletal biodiversity.”

Professor Zhong-Qiang Chen, head of the study, said: “Traces of fossils show us when and how soft digging animals thrived in this early Triassic greenhouse world.

“For example, high temperatures and prolonged anoxia coincided with low values ​​of behavioral and ecological diversity across the border between Permian and Triassic, and it took about 3 million years for ecological recovery of soft-bodied animals. Equivalent to pre-extinction levels.”

Professor David Bottjer, collaborator in the study from the University of Southern California, added: “One of the most notable aspects of the data from southern China is the extent of ancient environments that we were able to sample.

“Differentiated responses from infaunal ecosystems to varying environmental controls may have played an important but hitherto unappreciated evolutionary and ecological role in the recovery of the warm seas of the early Triassic.”

Dr. Chunmei Su, another contributor, said: “Mass extinction has killed over 90% of the species on Earth and we see this in the catastrophic reduction in the ecological function of surviving animals in the sea.

“In the beginning, there were only a few survivors, and the recovery started on deeper water. The necton recovery took place at the same time as the full recovery of engineering activities for wild ecosystems.”

Alison Cribb, a collaborator on the University of Southern California study, added: “The first animals recovered were pawn feeds such as worms and shrimp. Recovery of suspension feeds such as brachiopods, mosses and many mussels took much longer.

“Perhaps the depositors made so much mess in the seabed that the water became contaminated with mud, the ground mud meant that the suspension feeders could not settle properly on the seabed, or the muddy water produced by these deposit feeders simply clogs the filtration structures of suspension feeders and forbids them to feed. effectively. “

Professor Chen added: “And some animals, like corals, were completely gone. The coral reefs only returned much later.”

Dr. Feng concludes: “Why is it important to understand these great mass extinctions from the geological past?

“The answer is that the late Permian crisis – which was so devastating to life on Earth – was caused by global warming and ocean acidification, but sporadic animals can be selected by the Earth’s environment.” A way that skeletal organisms were not.

“Our fossil trace data reveals the resistance of soft animals to high CO2 and heating. These ecosystem engineers may have played a role in restoring the benthic ecosystem after severe mass extinctions, which could potentially trigger, for example, the evolutionary innovations and radiation of the early Triassic.

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