New Study Revises Estimate Of The Greatest Mass Extinction

Metalegoceras, which is a cephalopod related to the living chambered nautilus. Credit: Falls of the Ohio State Park, Clarksville, Indiana

A study published in the Proceedings of the National Academy of Sciences by Steven Stanley, paleontologist at University of Hawaiʻi at Mānoa, School of Ocean and Earth Science and Technology, revised estimates of the largest mass extinction to have taken place since animals appeared on Earth. It is undisputed that more than 250 million years ago, during the end-Permian “great dying” as it is commonly called, the number and diversity of marine species dropped catastrophically.

Stanley’s article introduces new methods for calculating the size of mass extinctions, that is, the percentage of species that died out during these crises. He devised a way to estimate the magnitude of background extinction—the extinction scattered throughout any mass extinction interval but having nothing to do with the mass extinction. Once Stanley had that number, he subtracted it out of the total to get a more accurate estimate of species loss.

“Most of these crises turn out to be less severe than previously believed, largely because people have calculated their magnitudes incorrectly by including background extinction,” said Stanley.

Cyclocrinites, a crinoid in the phylum Echinodermata suffered during the ‘great dying’ but survived and re-expanded. Credit: Fossils (Smithsonian Handbooks) by David Ward.

End-Permian crisis

There are several mass extinctions that stand out as having been extremely severe, and paleontologists have long recognized that the end-Permian crisis was the largest of all. A misleading scientific publication appeared in 1979 which mistakenly lumped together two mass extinctions and concluded that between 88% and 96% of marine species died out at the end of the Permian. This led to widespread claims that life nearly died out at the end of the Permian.

“Separating out the extinctions that actually occurred in the latest Permian, I have now estimated that the terminal Permian crisis eliminated only about 81% of marine species,” said Stanley. “About 90 orders and more than 220 families of marine persisted into the Mesozoic Era, the ‘Age of Dinosaurs,’ and they embodied an enormous amount of morphological, physiological and ecological diversity. Many of those species went on to diversify substantially. Life did not nearly disappear at the end of the Permian, as has often been claimed.”

This new study provides a more accurate picture of the history of life on Earth.