Microfossils that show up in large quantities in ancient rocks deposited during Earth’s largest mass extinction are fungal spores, not algae as some recent studies had proposed, new research suggests.
About 251 million years ago, at the end of the Permian period, life on Earth had its closest call: In a geologically short period of time, a mass extinction claimed more than 95 percent of species in the oceans and 70 percent of those on land (SN: 2/1/97, p. 74). But a few species bucked the extinction trend and proliferated at the time — in particular, those in the genus Reduviasporonites, says Mark A. Sephton, a geochemist at Imperial College London. In some cases, 100 percent of the organic matter found in rocks from the end of the Permian comes from Reduviasporonites.
Although researchers originally proposed that the Reduviasporonites spores came from fungi that feasted on the sudden bounty of dead woody plants, some recent studies have suggested that those fossils are the remnants of massive algal blooms, Sephton says. Now, he and his colleagues say in the October Geology, new analyses discount the algal explanation.
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The researchers took samples of rock deposited during the late Permian extinctions, used strong acids to dissolve the minerals and then analyzed the organic matter that remained. Tests reveal that the organic residues, including copious amounts of Reduviasporonites, don’t contain any breakdown products derived from chlorophyll, which is found in algae. The analyses also detected organic molecules containing ring-shaped structures called furans, a class of compounds not typically found in algae.
Finally, the team’s isotopic studies provide strong evidence for Reduviasporonites’ fungal identity. The ratio of two particular nitrogen isotopes in the material falls slightly outside the ratios characteristic of algae but well within the range of isotopic ratios in fungi.
“The weight of evidence is pushing toward a fungal origin,” says Paul Wignall, a paleontologist at the University of Leeds in England. Figuring out what Reduviasporonites really was will help scientists interpret the environmental conditions at the end of the Permian and therefore shed light on why mass extinctions happened then.
Whether these fossils represent fungi or algae, the mass extinctions would have provided a plentiful buffet of dead plants and animals. And for a brief while, microbial life may have dominated both land and sea. “If these things were fungi, it was an exceptionally strange ecosystem,” Wignall notes.