A METRIORHYNCHID CROCODYLIFORM BRAINCASE FROM NORTHERN CHILE

FERNÁNDEZ, M., PAULINA CARABAJAL, A., GASPARINI, Z., HERRERA, Y., CHONG, G.

Pittsburgh, USA

Congreso; 70th Annual Meeting of the Society of Vertebrate Paleontology; 2010

Metriorhynchids were a group of Mesozoic crocodyliforms completely adapted to a marinelifestyle. Although there are a large number of metriorhynchid skulls, mainly fromthe Middle and Upper Jurassic from the European margins of the Western Tethys, most ofthem have collapsed into a single layer. This has confounded accurate braincase descriptions.A three-dimensional metriorhynchid braincase of Metriorhynchus cf. westermannifrom the Oxfordian of northern Chile has excellent preservation and shows details of thesutures. X-ray computed tomographic (CT) scanning provides internal anatomical details.The general pattern of the orbitotemporal region is consistent with that described by otherauthors in the basal thalattosuchian Pelagosaurus typus. The specimen from northern Chileshares with other metriorhynchids (Cricosaurus araucanensis, Metriorhynchus westermanni,M. casamiquelai and Dakosaurus andiniensis) a dorsally exposed laterosphenoid, alaterosphenoid-prootic suture that forms a blunt crest separating the dorsotemporal fenestrainto two muscular fossae, and a quadrate that is incompletely sutured to the braincase. Themain difference in the orbitotemporal region is that in the Chilean specimen, and the othermetriorhynchids examined, the trigeminal fossa is mainly positioned caudal to the trigeminalforamen, whereas in Pelagosaurus typus it is rostral and caudal to the trigeminal foramen.The CT scans reveal the presence of enlarged dorsal dural venous sinuses overlying thebrain, a paired tube-like cavities connecting the cranioquadrate passage to the dorsal duralvenous sinus, and a well developed sinus within the quadrate. The large foramen ventrolateralto the occipital condyle, characteristic for metriorhynchids, is confirmed as the openingfor the internal carotid artery.