Stethacanthus

Stethacanthus was a prehistoric shark that lived during the late Devonian period 390-360 million years ago. Its fossils have been found in Europe and North America. Stethacanthus was an efficient marine predator that hunted small fish as well as other smaller sharks.

Stethacanthus had a strange protrusion on the back of the male sharks, often described as an "ironing board”. It is believed that this dorsal fin may have been used in mating rituals, or perhaps to frighten potential predators. Stethacanthus grew up to 6 feet long and weighed 100 pounds.