Piratosaurus (meaning "Multiplied pirate lizard") is a dubious genus of plesiosaur possibly belonging to the Polycotylidae[1] that is known exclusively from the type species P. plicatus, named and described by Joseph Leidy in 1865.[2] It is known only from the holotype, USNM V 1000, a tooth, discovered in Late Cretaceous-aged rocks in the Red River basin of Manitoba; at least one researcher erroneously assumed it was found in Minnesota.[3]