The researchers also found a slight increase in the frequency of drill holes on brachiopods in middle-to-late Paleozoic times and a second modest increase sometime after the end of the Paleozoic Era. Those findings hint at how the whole food chain was changing over time.

"These subtle increases in drill holes on brachiopods, from less than one percent in the early Paleozoic era to several percent today, suggest that predators have become increasingly abundant and active through the history of life," said Michal Kowalewski, an associate professor of geobiology at Virginia Tech. Over time, "the basic food supply in the oceans---phytoplankton---increased significantly, organisms up the food chain became more meaty, and predators---bony fish, snails and crustaceans---increased in frequency and diversified," he said. As predators specialized in attacking their shell-protected victims, prey groups also diversified and became better armored. As a result, the authors hypothesize, interactions between drilling predators and less desirable prey, such as brachiopods, became more frequent or more lethal.

"In a sense," Baumiller said, "we're using brachiopods as a dipstick to gauge the process of escalation."

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16-Jun-2005