had also unearthed several fossil specimens in the Chalk Formation, in which he assigned them as Pterodactylus compressirostris during its description. Owen later unearthed many fossil specimens from a different fossil site called the Cambridge Greensand, he then assigned these specimens into a new species called Pterodactylus simus. With the naming of this new species, British paleontologist Harry Govier Seeley created a new separate genus called Ornithocheirus (from Ancient Greek "ὄρνις", meaning "bird", and "χεῖρ", meaning "hand"), due to the notion of the time, in which pterosaurs were the direct ancestors of birds. In 1870, Seeley then also reassigned Pterodactylus cuvieri into a new species called Ornithocheirus cuvieri. This species is now considered to belong to the genus Cimoliopterus. Back in 1874 however, controversies between the naming of species and genera of these pterosaurs started, with the paleontologists Harry Seeley and Richard Owen fighting over reassignings of different species as well as genera. Owen therefore created two new genera: Coloborhynchus (meaning "maimed beak") and Criorhynchus (meaning "ram beak"), in reference to their unique convex "keeled" crests on top, and underside of their snout. Owen then created a type species for Coloborhynchus, C. clavirostris, and sunk three species which were assigned previously to Ornithocheirus, and Criorhynchus consisted entirely of former Ornithocheirus species. Later in 1881 however, Seeley disagreed with Owen's conclusions, and he therefore assigned the species he named Ornithocheirus simus as the type species of Ornithocheirus. The naming of the different pterosaur species, as well as the genus Ornithocheirus in England resulted in further research in other places. In the United States, American paleontologist Othniel Charles Marsh led an expedition to the Smoky Hill Chalk deposits in western Kansas in 1870. Marsh unearthed the first ever specimens of pterosaur from North America (specimens YPM 1160 and YPM 1161), which now belong to the genus Pteranodon, and consisted of partial wing remains and a tooth of the fish Xiphactinus, which Marsh had once believed that it belonged to Pteranodon. In 1871, he assigned these specimens to a new species called "Pterodactylus oweni" (meaning "Owen's wing finger"), in honor of Sir Richard Owen, but he realized that the name he had chosen had already been used for a different European pterosaur species described by Harry Seeley, so he renamed his discovery as Pterodactylus occidentalis (meaning "Western wing finger"), in reference to the location where it was found. American paleontologist Edward Drinker Cope