Predator-Induced Shell Damage in Bivalves from the Middle Devonian

The evolutionary importance of predator-prey interactions during the Paleozoic remains largely unknown for most taxonomic groups, geographic settings, and time intervals. Shell damage induced by durophagous (shell-breaking) predators has received less attention than traces of drilling predation. The main problem in identifying breakage-induced shell damage is its differentiation from other non-biological taphonomic processes. The presence of characteristic trace morphology and features of the repaired area (e.g., trace geometry, changes in growth line banding and loss or offsetting of ornamentation) are crucial in confirming a predatory origin of traces.

We report the oldest-known predator-induced shell damage in bivalves from a sample of 442 specimens of Middle Devonian bivalves from museum collections and field samples. These are primarily calcitic pterioids, such as, Ptychopteria, Actinopteria, Aviculopecten, and Pterinopecten, from central and western New York, which represent a conspicuous part of the epibenthos of the Hamilton fauna. All the studied genera lived either byssally attached or freely reclining on the soft substrate; specimens ranged between three and 10 cm in size. The overall repair frequency (total number of scars/ total number of shells in a sample) for our samples is 0.17, which is comparable to frequencies found among some modern bivalve species; for instance, the frequency of shell repair of modern bivalves ranges between an average of 0.13 for species with inflexible shell margins to 0.71 in pinnoids and pteriodean groups with flexible shell margins (Dietl and Alexander, 2005). Shell damage induced by durophagous predators of Paleozoic bivalves thus provides an untapped resource to evaluate the importance of ecological interactions in evolution set within the context of the “Paleozoic precursor to the Mesozoic marine revolution.”

Dietl, G.P., and Alexander, R.R. 2005. High frequency and severity of breakage-induced shell repair in western Atlantic Pinnidae (Bivalvia). Journal of Molluscan Studies 71(3):307-311.