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Paleontology

Getting Over an Extinction Crisis

extinction crisis

© G. Escarguel /CNRS Photothèque

While different groups of ammonites coexisted during the Permian (red), only one group, ceratites (green), survived the Permo-Triassic mass extinction.




Over the course of millions of years, the Earth regularly undergoes extinction crises during which biodiversity plummets. Then, a few species that survive the disaster diversify again. A group of laboratories in France and Switzerland, bridging decades of past data with extensive fieldwork and statistical modeling, has shown that this revival can happen astonishingly fast.1
The team found that in the wake of the Permo-Triassic mass extinction2 (252.6 million years ago), ammonites,3 an extinct group of marine animals, rebounded in merely one million years, and not in tens of millions of years as previously thought. “Relatively soon after the crisis, biodiversity started up again, and new species rapidly appeared in the oceans in masses, resuming levels of diversity comparable to those just before the event,” says Gilles Escarguel from the PEPS laboratory4 in Lyon, who worked on the project.
Researchers believe a single species, among the two or three that survived, is at the origin of the post-crisis diversification. They indexed 860 ammonite genera5 from 77 different past oceanic basins all over the world.
Some of the fossil samples were already present in databases from previous studies, and the remainder were collected over the past seven years mainly from the US and southern China (Guangxi). The field investigation is still taking place in Tibet and Pakistan. The specimens were hard to gather, since these mollusks typically do not fossilize during a crisis-event, due to the ocean's severely deteriorated conditions.
“Surprisingly, living beings actually regenerate much more quickly than the ocean retrieves its physical and chemical balance,” explains Escarguel.
This finding helps predict what might follow the sixth major extinction phase that our biosphere has currently entered. Recovery after a downfall spans tens of thousands of human generations, but is remarkably sturdy. According to Arnaud Brayard from the Biogeosciences laboratory6 in Dijon, who based his PhD work on this topic, “life always manages to survive somewhere and to rediversify, even if we're not sure exactly how this happens. It may take a long time, but it will eventually reappear.”

Melisande Middleton

Notes :

1. A. Brayard et al., “Good Genes and Good Luck: Ammonoid Diversity and the End-Permian Mass Extinction,” Science, 2009. 325: 1079-80.
2. Documented as the largest mass extinction over the past 550 million years, killing more than 90% of marine species.
3. Ammonites are fossil mollusks related to present-day octopus, squid, and cuttlefish.
4. Paléoenvironnement et paléobiosphère (CNRS / Université Lyon-I).
5. A genus is a set of closely related species.
6. Biogéosciences (CNRS / Université de Bourgogne).

Contacts :

Gilles Escarguel,
PEPS, Lyon.
gilles.escarguel@univ-lyon1.fr
Arnaud Brayard,
Biogéosciences, Dijon.
arnaud.brayard@u-bourgogne.fr


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