THE BRAINCASE OF A 3D PRESERVED PTEROSAUR FROM THE JURASSIC OF PATAGONIA

CODORNIÚ, L.S.; POL, D.; RAUHUT, O.W.; PAULINA CARABAJAL, A.

San Juan

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

The braincase of the specimen MPEF PV 3613, a pterosaur from the Middle Jurassic of the Cañadón Asfalto Formation, Chubut Province (Codorniú et al., 2010) is well- preserved and almost undistorted. No sutures are discernible between the braincase elements. The use of CT scans revealed aspects of the pneumaticity of the braincase that is affecting the paired frontals, supraoccipital, and basisphenoid. The parietal is approximately 60% the length of the frontal (excluding the nasal processes). The nuchal crest is almost at the same level with the skull roof in lateral view and is V-shaped in dorsal view. The supratemporal fossae are deeply excavated on the parietals, separated by a narrow sagittal crest. The frontal is mostly a flat element in the skull roof and the frontal postorbital processes are strongly projected laterally, each one having a large oval foramen posteroventrally that communicates internally with a pneumatic cavity. The occiput is mainly formed by the supraoccipital and the exoccipitals. Dorsolateral to the foramen magnum there is a large dorsal head vein foramen, and more laterally is a smaller postemporal fenestra. The paroccipital processes are dorsoventrally high, but short transversely. The metotic foramen for cranial nerves (CN) IX-XI open ventrolaterally to the occipital condyle and a single foramen for CN XII open just under and slightly lateral to the occipital condyle. The occipital condyle is smaller than the foramen magnum, subspherical, posteroventrally directed and has not a constricted neck. The basal tubera are anteroposteriorly elongate but transversely narrow structures. Ventrally, the basisphenoid is rhomboidal in outline, with a tapering anterior end. It has a moderately deep, elongate basisphenoid recess along its midline. The basipterygoid processes are slender, long and narrow, anteroventrally projected and separated over their entire length. In lateral view, the basipterygoid processes diverge at an angle of approximately 45° from the dorsal skull roof. The CN V foramen is oval and 4 mm diameter. The postorbital process of the laterosphenoid is a narrow triangular projection adjacent to the posteroventral side of the postorbital process of the frontal. A ventral and narrow projection of the laterosphenoid is probably forming the anterior margin of the CN V foramen. Comparisons with the braincases of other pterosaurs, reveal a mosaic of characters in the Argentinean specimen, which shares some traits with “rhamphorhynchoids” but also with pterodactyloids taxa. Preliminary phylogenetic analysis places the taxon in a polytomy with the recently described Darwinopterus (Lü et al., 2010) at the base of the Pterodactyloidea (Codorniú et al., 2010).