PREDATORY BORINGS PROVIDE NEW INSIGHTS ON THE PALEOECOLOGY AND SYSTEMATIC PLACEMENT OF HEDERELLIDS, COMMON ENCRUSTERS IN THE DEVONIAN OF OHIO

Hederellids are colonial encrusters found on marine hard substrates from the Silurian into the Permian. They are especially common in the Devonian, encrusting rugose corals, brachiopod shells, stromatoporoids, pebbles, cobbles, and hardgrounds. Some of the best preserved colonies are found in the Middle Devonian of upper midwestern North America, including northwestern Ohio. Hederellids look superficially like cyclostome bryozoans with long tubular zooids composed of non-porous calcite. This is, in fact, how they are often classified in paleoecological and systematic studies. However, unlike bryozoans, their maximum zooidal diameter (1.5 mm) is relatively large (in bryozoans is it less than 0.5 mm), zooidal budding occurs from a stolonal tube in many species, and their fibrous wall structure contrasts with the lamellar microstructures of Paleozoic bryozoans. Like most encrusters, the hederellids were undoubtedly suspension feeders, probably employing tentaculate feeding organs to capture plankton.

We have recently found small predatory borings drilled into some species of hederellids in the Middle Devonian of Ontario, New York and Ohio. We know these elliptical holes, about 0.2 to 0.3 mm in diameter with beveled edges, penetrated the skeletons of living zooids because they were often repaired from the inside using skeletal patches. These patches resemble repairs found in a modern cheilostome bryozoan, Microporella hyadesi (Jullien) from the South Atlantic.

Based on their skeletal morphology, microstructure, and response to drilling predation, we suggest that the hederellids were neither bryozoans nor corals (another group to which they have been assigned in the past). Instead, it seems possible that they were phoronid-like invertebrates with retractable lophophores.