ScienceDaily (May 8, 2012) -- A basic tenet underpinning scientists' understanding of extinction is that more abundant species persist longer than their less abundant counterparts, but a new University of Georgia study reveals a much more complex relationship.

A team of scientists analyzed more than 46,000 fossils from 52 sites and found that greater numbers did indeed help clam-like brachiopods survive the Ordovician extinction, which killed off approximately half of Earth's life forms some 444 million years ago. Surprisingly, abundance did not help brachiopod species persist for extended periods outside of the extinction event.

Study co-author Steven Holland, a professor of geology in the UGA Franklin College of Arts and Sciences, said the seemingly paradoxical finding suggests that predicting which species are at risk of extinction is an extremely dicey endeavor.

"This study shows that extinction is much more complicated than generally realized," said Holland, whose findings appear in the current issue of the journal Paleobiology. "It turns out that a lot of extinction events are idiosyncratic; there are a specific set of circumstances that come together and dictate whether something goes or doesn't."