TERROR IN MINIATURE: TROPHIC INTERACTIONS IN A SHELLY FAUNA OF THE PENNSYLVANIAN OF SOUTHERN OHIO

Fossil evidence of predation provides important clues to ancient trophic relationships. However, small-bodied predators and their victims are often overlooked in the fossil record. In a large fossil sample from the Middle Pennsylvanian Vanport Shale of southern Ohio, examples of shell damage from both predation and parasitism are common, as originally described by Dr. R. D. Hoare and others in 1980. This fauna includes numerous small animals (<15 mm) showing shell damage, including the brachiopod Composita, the nautiloid Pseudorthoceras knoxense, and the gastropod Microdoma conicum. Damage includes pitting, apertural breakage, and boreholes, all believed to have formed while the victim was alive.

To better characterize and examine these types of shell damage, selected specimens of brachiopods, nautiloids, and gastropods were digitally imaged and/or photographed under an Hitachi S-2700 scanning electron microscope. Examples of modern sponge boring and predatory gastropod drilling were also photographed for comparison with the fossil material. The images reveal details about the pits and borings, including morphology and severity, and highlight some similarities in the types of damage. The parasitic or epibiont pits are semi-organized into clusters; each pit is relatively shallow, with one end deeper and more steep-sided than the other, very rough sides, and a more ovular shape. These pits may have been produced by algae, hydroids, or some other unknown soft-bodied epibiont, attached at an angle to the shell. Numerous specimens of Composita sp. and five of approximately 600 (0.8%) M. conicum specimens show classic predatory boring--single, round, smooth-sided holes that penetrate perpendicular to the shell. The holes resemble those produced by the gastropod Platyceras, although other potential predators cannot be ruled out. The damaged shells provide a tantalizing glimpse into the trophic interactions of these tiny animals.