Description of the skull of a Ctenochasma (Pterosauria) from the latest Jurassic of eastern France, with a taxonomic revision of European Tithonian Pterodactyloidea

ABSTRACT

A Ctenochasma specimen from the latest Jurassic of eastern France is described in detail and referred to Ctenochasma sp. The preserved braincase of this specimen has a bird-like lateral position of the optic lobes, with proportionally a smaller size than in birds, the bones surrounding it being thick and hollow.

An original biometric analysis, based on skull length and tooth number, has been performed using a selection of Late Jurassic Pterodactyloidea of Europe. This study suggests that Ctenochasma gracile and Ctenochasma porocristata are senior synonyms of Pterodactylus elegans and Pterodactylus antiquus of Pterodactylus kochi. It also reveals that Pterodactylus elegans may be transferred to Ctenochasma. These results obtained with biometric analyses are confirmed by morphological observations. This study could not determine if Pterodactylus micronyx is a juvenile of C. roemeri, the Ctenochasma of Saint Dizier or Gnathosaurus subulatus. Because this species is only composed of juveniles, more data are needed to determine its adult morphology. The genus Ctenochasma is thus represented by three species, C elegans, C. roemeri and C. sp., and Pterodactylus by two, P. antiquus and P. longicollum, all from the Late Jurassic of Germany and France. This study points out a biological anomaly: all the teeth are not present in a hatching pterosaur, but their number increase progressively during growth, with new teeth erupting from the front of the jaws. This phenomenon is particularly spectacular in Ctenochasma elegans, where the tooth number increases progressively from 60 to more than 400 teeth during growth.