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'The Great Dying' May Not Have Been So Great

New findings suggest that the formerly agreed-upon rates of terrestrial extinctions may be inaccurate.
Rachel Pick
New York, US
Dicynodon lacerticeps. Image: Nobu Tamura

The end of the Permian geological period 252 million years ago is known colloquially as The Great Dying, as 96 percent of marine species and 70-75 percent of terrestrial species are estimated to have been killed off around that time. While the near-total extinction of aquatic life is still unquestioned—and may soon repeat itself, if we're not careful—new findings suggest that the formerly agreed-upon rates of terrestrial extinctions may be inaccurate.

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The changeover in the rock record from fossils of Dicynodon, a genus of therapsid that looks like a combination hippo and Komodo dragon, to Lystrosaurus fossils had previously been used to mark the dying-off of Permian-era species and the beginning of the Triassic period. But Dicynodon is now thought to have died out a million years before the extinction took place.

Researchers in South Africa's Karoo Basin found zircon crystals, formations that tend to produce reliable dating information for the surrounding rock. As Science News reports, the zircon crystals date to 253.48 million years ago, and were found 60 meters below a layer of rock showing the change from Dicynodon to Lystrosaurus. Using the rate of rock accumulation in the basin, the geologists determined that the 60-meter span took 200,000 to 300,000 years to form, placing the Dicynodon extinction approximately 1.3 million years before the date of the Permian extinction in the oceans.

The team's research states that "the currently accepted model of the terrestrial ecosystem response to the crisis, both in this basin and its extension globally, requires reevaluation." But others disagree. South African paleobiologist Jennifer Botha-Brink told Science News, "People forget that biology is messy. You can never draw a line of when the extinction was. It's an interval; it's a changeover." Botha-Brink points out that the accumulation of new rock isn't necessarily constant, and that could have skewed the team's findings in the wrong direction.

One thing is certain: it is crucial that we do further research into this chaotic period in the Earth's history, and how the planet recovered from it—because we are already in the middle of our own major extinction event.