The actinopterygians are the group of fishes ancestral to all the ray-finned fishes. Everything from the seahorse up to tuna belongs to the ray-finned fishes, some 20,000 or more species.
The only actinopterygian found in the Middle Devonian sediments of Orkney is the species Cheirolepis trailli. This species is one of the earliest complete fishes collected from this group and described in several publications.
Cheirolepis was a slender fish with one dorsal fin and jaws with rows of tiny but sharp teeth.
Probably they had to share the lake with the other top predators the crossopterygians.
The head is covered with medium sized bony plates and the body is covered with bony scales with sharp ridges on the surface. The scales are generally smaller than one millimeter.