A well preserved skull of Cymatosaurus (Reptilia: Sauropterygia) from the uppermost Buntsandstein (Middle Triassic) of Germany

摘要

A sauropterygian skull from the uppermost Buntsandstein (earliest Anisian, uppermost R?t-Formation, C?lestinschichten) of Wogau (Thuringia, eastern Germany) is described in detail and assigned to a new species of Cymatosaurus, Cymatosaurus erikae. Cymatosaurus erikae n. sp. differs from all other species of the genus by a unique combination of dental and cranial features, including nasals that do not reach the external naris or the anterior margin of the orbit, frontals that do not enter the orbital margin and closely approach but do not enter the temporal fenestra, at least two maxillary teeth anterior to the fangs, a long parietal that extends up to the orbit and narrows posteriorly without forming a sagittal crest, unfused vomers, narrow and elongate palatines, and inclined quadrates and quadrate condyles. The new specimen shows a completely closed palate as in nothosaurids, but retains an open occiput. A small lacrimal (recorded here for the first time in Cymatosaurus) is probably present. These features are plesiomorphic for sauropterygians. This combination of features makes it conceivable that Cymatosaurus might actually be a stem-nothosaur rather than a stem plesiosaur, as previously suggested. A phylogenetic analysis of Cymatosaurus species indicates that C. erikae is the sister-taxon of C. latifrons and C. fridericianus. Cymatosaurus gracilis (Schrammen, 1899) is reconsidered and re-established as a valid species of the genus, contrary to previous suggestions.