A DUNKLEOSTEUS SUBORBITAL FROM THE CLEVELAND SHALE, NORTHEASTERN OHIO, SHOWING POSSIBLE ARTHRODIRE-INFLICTED BITE MARKS: EVIDENCE FOR AGONISTIC BEHAVIOR, OR POSTMORTEM SCAVENGING?

The Cleveland Shale Member (Late Devonian, Fammenian) of the Ohio Shale in northern Ohio is a well-known vertebrate Konservat-Lagerstätten whose most famous taxon is arguably the giant arthrodire Dunkleosteus terrelli. Collected from the Cleveland Shale in 1925, the Cleveland Museum of Natural History’s specimen CMNH 5302 is an isolated left suborbital from D. terrelli that possess several notable modifications to the bone. A series of gouges and scratches are present on the lateral surface of the plate. There is a large hemi-spherical break posteriorly at which the largest surficial gouge terminates. The position of this gouge and the morphology of the break are consistent with the actions associated with a puncture made by the anterior bite margin of a Dunkleosteus infragnathal. This break and the other surficial gouges are best interpreted as bite marks inflicted by another large arthrodire, likely another Dunkleosteus. Additionally, the surficial gouges are aligned in two separate sets of orientations, suggesting that they were applied to the bone during at least two distinct biting events.

Any physical evidence of intraspecific interaction in the fossil record is potentially of great importance, as these instances provide the only unequivocal evidence for intraspecific behavior in extinct organisms. CMNH 5302 can be interpreted as evidence of intraspecific aggression and possible intraspecific predation in Late Devonian arthrodires. Conversely, the gouges may be taphonomic in nature, inflicted postmortem before the Dunkleosteus was buried in the anoxic bottom sediments.