UCSB researcher leads worldwide study on marine fossil...(/p We only count it where we've actu...)

"We only count it where we've actually got it," Alroy said. "Say you're doing biomedical research and you want to know about the prevalence of a disease, say some kind of cancer."

The difference between the old and the new research, he said, would be like "the difference between checking medical records willy-nilly, and computing percentages with a standardized sample."

While the research of other scientists showed eventual recoveries in the diversity of fossils after periods of extinction - especially the extinction 250 million years ago between the Permian and Triassic periods (also known as the "mother of all mass extinctions") - Alroy said this report shows that the number of species comes back up quickly - at least on a geological time scale - and then stays relatively flat.

The data are also interesting, Alroy said, because they document that there have been only three truly major mass extinctions in the fossil record.

"For many years, our community has been saying that there have been five major mass extinctions, and it's gotten into the public consciousness that there's been a 'Big Five,' " Alroy said. "This (the last major spike in fossil diversity records) is supposed to be the sixth major extinction. This is really conventional wisdom, but it's not supported by the new data at all."

Instead, the new results suggest it's only the fourth one over the last half-billion years.

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