Stethacanthus (Latin: Stethacanthus) is a genus of whole-headed fish that lived 370-345 million years ago in the seas of what is now North America, Europe, and Russia. Outwardly, the Stethacanthus resembled a shark 70-200 cm long. The dorsal fin of this fish had a modified shape, resembling an ironing board. On it, as well as on the head, there were small spines - modified skin denticles that are present in modern sharks. Most likely, this modified fin served to attract attention or scare off larger predators.