But it doesn't always happen that way, and investigating systems in which prey don't respond to predation by upping the ante can be as informative as studying the more typical sort, said University of Michigan paleontologist Tomasz Baumiller. In a report in the June 17 issue of Science, Baumiller and collaborators at Virginia Tech describe how they used fossil shells of animals called brachiopods to shed light on ancient ecological interactions.
Brachiopods, also known as lampshells, were plentiful in Earth's oceans 550 million years ago to 250 million years ago. Today the shelled creatures, which look something like clams, are still around but less prevalent. One way of assessing rates of predation or parasitism on brachiopods and other fossil shellfish is to look for round holes drilled into their shells by their enemies. The researchers studied more than 40,000 specimens from 18 museums, as well as field-based estimates from the literature.
"We wanted to determine at what frequencies drilling had occurred, whether that had changed through time, and what sorts of lessons we could learn from the patterns that we found," Baumiller said. What they found was that attacks on brachiopods were rare, but widespread and continuously present through the entire Paleozoic Era, suggesting that brachiopods were not locked in an arms race with drilling predators. Instead, predators probably picked on brachiopods only when they mistook them for something else or when there was nothing better to eat, the researchers believe.
"The reason is, they're not terribly nutritious---they have a relatively low amount of meat between their shells," which also may explain why you never see brachiopod c