Approximately 252 million years ago, about 90% of the creatures that lived on Earth disappeared. It is, for now, the most serious extinction event in history and, for this reason, it is known as the “Great Dying”. A new study concludes that the animals that first recovered from the catastrophe, both in number and in biodiversity, were those that feed on the organic matter found at the bottom of the ocean, such as earthworms and shrimp . These creatures are known as reservoir feeders.
Tank feeders were followed much later by suspension feeders, that is, those that ingest organic matter that, instead of being at the bottom, is found on the surface of the water. Knowing this has been possible thanks to a detailed dating of the traces and burrows of the seafloor of southern China. The analysis found a large number of ichnofossils or trace fossils , which are not animal remains as such, but remains of animal activity.
“We were able to look at trace fossils from 26 sections throughout the entire series of events, representing a crucial 7 million years of time,” says paleontologist Michael Benton of the University of Bristol in the UK. “Showing details across 400 sample points, we finally reconstructed the recovery stages of all animals, including benthos, nekton, as well as these soft-bodied, ocean-burrowing animals.”
These types of trace fossils are vital to understanding how soft-bodied animals lived , as they have no bones to leave behind. The researchers have also worked with body fossils to find out how other species began to recover once deposit feeders became established.
“The end-Permian crisis – which was so devastating to life on Earth – was caused by global warming and ocean acidification, but animals that feed on traces can be selected by the environment in a different way. that skeletal organisms were not,” says paleoecologist Xueqian Feng of the China University of Geosciences. “Our fossil data reveals the resistance of soft-bodied animals to elevated CO2 and warming. These ecosystem engineers may have played a role in the recovery of benthic ecosystems after severe mass extinctions, for example, trigger evolutionary innovations and radiations in the early Triassic.”
To measure recovery, scientists have looked at a number of metrics: diversity (different types of an animal), disparity (how varied those types are), how they use space, and how habitats were changed by animals.
After the “Great Dying” it is believed that life returned to the deep waters first. Most of the deposit-eating organisms were recovered first. Much later would come the brachiopods, bryozoans and bivalves, which are usually rooted to the bottom. Later the corals would still return. The soft-bodied settlers of the sediments took about 3 million years to return to pre-extinction levels.
“Perhaps the reservoir feeders fouled the seafloor so much that the water became contaminated with mud, the churning mud caused the suspension feeders to not settle properly on the seafloor, or the muddy water produced by those reservoir feeders just clogged filter structures of suspension feeders and prevented them from feeding effectively,” says Alison Cribb of the University of Southern California.
The Permian-Triassic extinction known as the “Great Dying” wiped out 80-90% of our planet’s marine life, so it’s not surprising that recovery took a long time to happen. By adding data from trace fossil records along with body fossils, scientists can learn more about what happened after the extinction.
Climate change, global warming, declining oxygen and increasing ocean acidification are believed to have been responsible for the “Great Dying”. The findings of this study may give us insight into how these creatures might survive the current warming period , and which species might be the most resilient.
Referencia: Feng, X. et al. 2022. Resilience of infaunal ecosystems during the Early Triassic greenhouse Earth. Science Advances. DOI: 10.1126/sciadv.abo0597.
