Helicoprion is an extinct genus of cartilaginous fish. Almost all fossil specimens are of spirally arranged clusters of the individuals' teeth, called tooth whorls, which in life were embedded in the lower jaw. As with most extinct cartilaginous fish, the skeleton is mostly unknown. It is one of the most popular sharks of all time. It was always assumed that the "Helicoprion" was a shark, but it is more closely related to ratfish.