Signs of boring predation on Middle Devonian hyolithids from the Michigan Basin

A large number of specimens (∼500) of the hyolithid Hallotheca cf. aclis (Hall) were collected from the Middle Devonian Arkona Shale at Hungry Hollow, Ontario, Canada. This is an unusually large sample for Devonian hyolithids and only the second record of hyolithids from the Michigan Basin. Furthermore, the conchs of seven specimens are bored, and the holes are single, complete, circular in plan view, and with their long axes perpendicular to the walls of the conch. These traits and the fact that the holes are stereotyped with respect to the side of the conch—all occur on the venter—are consistent with a predatory origin of the holes. Although bored specimens represent only ∼1% of the sample, this record expands the taxonomic breadth of bored prey during the middle Paleozoic, a time previously recognized as characterized by intensification of predator-prey interactions.