Recent work by paleontologists Tomasz Baumiller of the University of Michigan and Forest Gahn of the Smithsonian's National Museum of Natural History offers new insights into the process. A report on their research appears in today's issue of Science.
Biologists long have speculated that predators and prey play a game of evolutionary one-upsmanship, in which an adaptation on the part of one---say, sharper teeth in a predator---prompts a "go-you-one-better" response in the other---tougher hide in the prey, for instance.
Hints that this has occurred are scattered throughout the fossil record, but not evenly, Baumiller said. During one part of the Paleozoic Era known as the Middle Paleozoic Marine Revolution, for example, the diversity of shell-crushing predators increased explosively. Around the same time, some 380 million years ago, mollusks and other shell-bearing marine animals developed better protective devices, such as more spines or more tightly-coiled shells.
Apparently, the prevalence of shell-crushers prompted development of better defenses against them. But simply finding evidence of changes in both predators and prey doesn't prove that one caused the other, Baumiller noted. "You have to provide evidence that they, in fact, were interacting."
To search for such evidence, Baumiller and his former graduate student Gahn, studied fossil crinoids, a group of marine animals related to starfish and sea urchins. Crinoids, also called sea lilies, have feathery arms that they extend to catch bits of plankton or detritus passing by in the current.
Like their starfish cousins and other animals in the group known as echinoderms, crinoids are capable of regenerating lost body parts. Because modern day crinoids usually lose---and regenerate-
Contact: Nancy Ross-Flanigan
University of Michigan