A METRIORHYNCHID CROCODYLIFORM BRAINCASE FROM NORTHERN CHILE.

FERNANDEZ M. S.; PAULINA CARABAJAL, A.; GASPARINI, Z.; HERRERA, Y.; CHONG, G.

Pittsburg

Otro; Society of Vertebrate Paleontology annual meeting; 2010

Society of Vertebrate Paleontology

Metriorhynchids were a group of Mesozoic crocodyliforms completely adapted to a marine lifestyle. Although there are a large number of metriorhynchid skulls, mainly from the Middle and Upper Jurassic from the European margins of the Western Tethys, most of them are preserved compressed and confounded accurate braincase descriptions. A three dimensionaly preserved metriorhynchid braincase from the Oxfordian of Northern Chile, referred to Metriorhynchus cf. westermanni, is described. The excellent preservation provides accurate sutures and a detailed description. X-ray computed tomographic (CT) scanning provided internal anatomical details. The general pattern of the orbitotemporal region is consistent with that described by other authors in the basal thalattosuchian Pelagosurus typus. The specimen from Northern Chile shares with other metriorhynchids compared (Cricosaurus araucanensis, Metriorhynchus westermanni; M. casamiquelai and Dakosaurus andiniensis) a dorsally exposed laterosphenoid, the laterosphenoid-prootic suture forming a blunt crest separating the dorsotemporal fenestra into two muscular fossae, and the quadrate incompletely sutured to the braincase. The main difference in the orbitotemporal region is that in the specimen described herein, and the other metriorhynchids examined, the trigeminal fossa is developed mainly caudal to the triageminal foramen, whereas in P. typus the fossa is developed rostral and caudal to the trigeminal foramen. Internal exploration indicates the presence of enlarged dorsal dural venous sinuses overlying the brain and a well developed sinus within the quadrate. The larged foramen ventrolateral to the occipital condyle, that characterizes metriorhynchids, is confirmed as the entry for the internal carotid artery during life.