Isotelus maximus Locke, 1838 trilobite with healed bite mark from the Arnheim Formation (Upper Ordovician) of southwestern Ohio’s Flat Run Trilobite Lagerstätte (public display, Orton Geology Museum, Ohio State University, Columbus, Ohio, USA).

Trilobites are important and common fossils in Paleozoic rocks, especially in the Cambrian. Much is known about their paleobiology, ontogeny, evolutionary patterns, etc. One of the less well known aspects of trilobitology is the significance of malformations, or deformities in the preserved exoskeleton. One category of trilobite malformation is healed bite marks, which can be seen here.

This large outstretched specimen has a healed injury on the right side of the cephalon (head). The exoskeleton has partially regenerated and a small, anomalous genal spine has started growing. The regenerated exoskeleton indicates that the injury was not lethal - the bite mark is evidence of unsuccessful predation.

This trilobite specimen, plus the large enrolled Isotelus specimen shown elsewhere in this photo album, have healed bite marks on their right sides. Published census information of bitten trilobites has shown that a statistically significant percentage of specimens have bite marks on their right sides. This is a great example of “handedness” (behavioral lateralization) in the fossil record.

Note: Examination of this specimen by the trilobite research Danita Brandt has resulted in a re-interpretation of the malformation present on the right side. This may be a healed injury sustained during molting, rather than a healed predatory bite mark.

Classification: Arthropoda, Trilobita, Polymerida, Asaphidae

Stratigraphy & age: Flat Run Trilobite Lagerstätte, near-top Sunset Member, mid-Arnheim Formation, lower Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician

Locality: Flat Run Trilobite Quarry, far-southern Clay Township, far-southwestern Highland County, just E of Sicily, E of Mt. Orab, southwestern Ohio, USA.

Collected & prepared by Dan Cooper.

Published references on bitten and malformed trilobites:

Babcock & Robison (1989) - Nature 337: 695-696.

Babcock (1993) - Journal of Paleontology 67: 217-229.