Isotelus (Trilobita) “hunting burrow” from Upper Ordovician strata, Ohio

Abstract

Recurring associations of the trilobite ichnogenus Rusophycus with various “worm” burrows suggest an interaction between the two tracemakers, specifically, capture of the worm by the trilobite. An exceptional ichnofossil from the Upper Ordovician of southwestern Ohio shows characters consistent with previously described “trilobite hunting burrows” from Cambrian and Silurian strata. Preserved in convex hyporelief is R. carleyi, attributable to the trilobite Isotelus, on which is superimposed the case of a worm burrow of the ichnogenus Palaeophycus. The cast of the worm burrow appears to have been truncated by the digging activities of the trilobite, suggesting its predation of the worm. The exquisite preservation of ventral axial morphology of the trilobite distinguishes this Rusophycus from simpler bilobate forms attributable to filter-feeding behavior. Congruency in the preservation of worm and trilobite trace supports the conclusion that both were created at the same time, as the trilobite exited the intrastratal burrow. This is the first report of a trilobite hunting burrow from the Ordovician, and the first evidence for predatory behavior for the trilobite genus Isotelus.