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.