A smaller shark, the Stethacanthus grew to just 3 feet (1 meter) long. Its name, which translates to “chest spike,” came from the flat protrusion on the backs of the male sharks.

It’s thought that they used it to attach themselves to female sharks when mating. It also slowed their movements considerably. The Stethacanthus were likely bottom-feeders rather than speedy predators.

They lived in North America, Asia, and Europe. The species died almost 300 million years ago.