The braincase of a 3D preserved pterosaur from the Jurassic of Patagonia

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

San Juan

Congreso; IV Congreso Latinoamericano de paleontología de vertebrados; 2011

Museo de Ciencias Naturales, Universidad Nacional de San Juan

The braincase of the specimen MPEF PV 3017, a pterosaur from the Middle Jurassic of the Cañadón Asfalto Formation, Chubut Province (Codorniú et al., 2010) is well-preserved and almost undistorted. The use of CT scans revealed aspects of the pneumaticity of the braincase that is affecting the paired frontals, supraoccipital, and basisphenoid. No sutures are discernible between the braincase elements. The parietal is 60% the length of the frontal (excluding the nasal processes). The nucal crest is tall and 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. Dorsolaterally to the foramen magnum there is a large dorsal head vein foramen, and more lateral is a smaller postemporal fenestra. The paroccipital processes are dorsoventrally high, but short transversely. The metotic foramen and a single foramen for CN XII open 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. The ventral side of 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 separate 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 cranial nerve V foramen. Comparisons with the braincases of other pterosaurs, reveal a mosaic of characters in the Argentinean specimen, which shares some traits with rhamphorhynchid but also with pterodactyloid taxa. A preliminary phylogenetic analysis of the specimen, locates it as the sister taxon of pterodactils.