The genus Gnathosaurus contains two species. There is the type G. subulatus and a second named G. macrurus from farther afield. Gnathosaurus seems to have been rather wide-ranging, with the type species found in the famed Solnhofen Limestone and the second found in England's Purbeck Limestone. The latter is a marine formation in Dorset with fossils from the very end of the Jurassic, and converging upon the very beginning of the Cretaceous.
It was another oceanic pterosaur from the Late Jurassic, similar to many other Solnhofen pterosaurs and its first fossils were thought to be a part of a marine crocodile. These finds were discovered in 1833, while the British remains were documented later. It was a filter-feeder like its contemporary Ctenochasma, and was a member of the same family. Its wingspan was nothing special, at around 1.75 meters across.