Falcatus is a Carboniferous shark. It is known as a unicorn shark. It may hunted smaller fish that lived in the ocean. However, in 1985, fossils of a new type of condrichthyan from Montana were described that displayed a high degree of sexuel dimorphism. The same spines that were previously named P. falcatus were found on one of the morphs, identified as the male due to the presence of valvae.