Gnathosaurus subulatus (von Meyer 1833, B St AS VII 369, No. 69 of Wellnhofer 1970; PTHE 1951.84 Mayr 1964, No. 70 of Wellnhofer 1970)~28 cm skull length, is known only from a mandible and referred skull. The mandible and skull were not associated and may not be related, but in the absence of competing data, the tradition of placing them together is followed here. Both are many times larger than in AMNH 5147.
The mandible was was originally considered a bizarre little crocodilian. The "matchin"g skull was described by Mayr (1964).
Distinct from AMNH 5147, the larger and longer skull of Gnathosaurus had a spoon-shaped premaxilla. The jaws were flanked by ~130 needle-like teeth oriented laterally. The lateral teeth project anterolaterally. The entire orbit was posterior to the mandibular articulation. The basispterygoids were in medial contact.
Several paleontologists, such as Christopher Bennett, have suggested that a purported tiny Pterodacytlus?micronyx? (CM 11 426), is likely a juvenile of Gnathosaurus. This is incorrect. Only one specimen, AMNH 5147, tested here nested with Gnathosaurus, and it was a tiny, more primitive adult. We know from Pterodaustro and the JZMP embryo that hatchlings of genera that had an elongated rostrum and small eyes also had an elongated rostrum and small eyes. They did not have a short rostrum and large eyes, like embryo mammals, birds and crocodilians did. Note that the IVPP embryo did have a short rostrum, but so did all of its adult sister taxa.
See more ctenochasmatids here. The dorygnathid tree is here. The pterosaur family tree is here.