What Was Eating Clams And Brachiopods 250 Million Years Ago, Before Modern Predators?

Alan Hoffmeister of Cincinnati, Ohio, a geological sciences student at Virginia Tech, will present his research at the 50th annual meeting of the Southeastern Section of the Geological Society of America (GSA), April 5-6 in Raleigh, N.C.

Hoffmeister is studying a collection of fossils from the late Paleozoic (290 to 250 million years ago), which was gathered from the Glass Mountains in West Texas over a 40-year period by G. Arthur Cooper. The collection is housed at the Smithsonian. So far, out of 3,140 brachiopod specimens, Hoffmeister has identified 58 unquestionable drill holes. Of 654 clams, 23 had definite drill holes. This is the earliest finding of drilling in clams and the first time either group has been studied in a quantitative way in Permian rocks, Hoffmeister says. The finding has evolutionary and ecological implications, he says. "This data may support the hypothesis of escalation, proposed in the mid 1980’s by Gary Vermeij. The hypothesis says that when a species is subject to predation, it evolves defenses, such as a thicker shell or ornamentation, to combat being eaten. The predator may then evolve strategies to overcome these defenses," Hoffmeister explains. "This is a major interactive force in benthic marine ecosystems today."

Ecologically, the drilling represents a new type of pressure on organisms that lived millions of years ago. "But it also expands the use of potential food resources within the ecosystem. Drilling represents a novel method of predation and gives us a good indication of individual interaction. You don't often see evidence of this kind of interaction from millions of years ago. But here you see a hole in the victim. It's a record that helps expand ecological understanding."

At Raleigh, Hoffmeister will present his findings in the context of subsequent instances of drilling, pointing out that drilling increased from less than 2 percent from the late Paleozoic to more than 30 percent in more recent Miocene deposits, only seven million years old. In this time frame clams replaced brachiopods as the dominant bivalved organism in the marine ecosystem. He points out that brachiopods don't offer much nourishment for the energy required to drill them.

Therefore, Hoffmeister conjectures that brachiopod drilling may be a result of parasites that had attached in order to snag crumbs as the brachiopod suctioned and filtered its own dinner. Co-authors of the paper, "Evidence for predatory drilling in late Paleozoic brachiopods and mollusks from West Texas," are Michal Kowalewski and Richard Bambach, faculty members in geological sciences at Virginia Tech, and Tomasz Baumiller of the Museum of Paleontology at the University of Michigan. The talk will be at 9:20 a.m. April 6 in the Sheraton Capital Center Hotel in Raleigh.