New Fossils Threaten an Extinction Theory

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Recent discoveries of long-gone marine invertebrates call into question the occurrence of a catastrophic global extinction hundreds of millions of years ago. The loss of diversity wasn't as widespread and didn't last as long as paleontologists had previously thought, several researchers now suggest.

The extinction during the Late Devonian period is widely considered one of the five massive extinctions in Earth's prehistory. The die-off climaxed at the end of the period's Frasnian stage, which lasted from around 385 million to 375 million years ago. The extinction began an extended interval of low biodiversity known as the Famennian stage. Coral reef ecosystems collapsed at the Frasnian-Famennian transition, and their gradual recovery took about 20 million years, until the end of the Devonian, many researchers say.

New data, however, suggest that at least some marine organisms rebounded quickly during the Famennian. Johnny A. Waters of the State University of West Georgia in Carrollton and his colleagues searched for fossils of echinoderms, a class of marine invertebrates, at Famennian sites in Australia, China, Morocco, and elsewhere. Their intent was to flesh out a fossil record previously known mostly from Appalachian and Swiss Alps deposits. Records at these sites suggested that the Late Devonian saw a prolonged drop in echinoderm diversity consistent with a mass extinction.

Waters and his colleagues identified many more echinoderm taxa in Famennian sediments worldwide than other paleontologists had presumed were there. "The Famennian was a time of major evolutionary innovation for echinoderms," says Waters. He suggests that reefs in many parts of the world rebounded quickly from a brief Frasnian extinction, but a bias toward research in North America and Europe obscured that pattern.

Previously studied reef devastation may have been limited to only one of Earth's hemispheres, Waters says. …