From Ohio History Central
Acanthodians were among the earliest fishes with jaws and are found in Silurian through Permian rocks. Their fragmentary remains are found in Devonian, Mississippian, and Pennsylvanian rocks in Ohio. These remains consist of shiny, rhomboid-shaped scales and fin spines. Fin spines of a comparatively large acanthodian, Machaeracanthus, are found in the Columbus Limestone.