A METRIORHYNCHID CROCODYLIFORM BRAINCASE FROM NORTHERN CHILE.

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

JOURNAL OF VERTEBRATE PALEONTOLOGY

SOC VERTEBRATE PALEONTOLOGY

Año: 2011 vol. 31 p. 369 - 377

0272-4634

A three-dimensionally preserved metriorhynchid braincase from theOxfordian of northern Chile is described. The specimen is referred to the metriorhynchidMetriorhynchus cf. M. westermanni. The excellent preservation provides clear sutures and adetailed description, and X-ray computed tomographic (CT) scanning provides internalanatomical details. The general pattern of the orbitotemporal region is consistent with thatof the basal thalattosuchian Pelagosaurus typus as described recently. The specimen fromnorthern Chile shares with other metriorhynchids (e.g., Cricosaurus araucanensis,Metriorhynchus westermanni, M. casamiquelai, and Dakosaurus andiniensis) a dorsallyexposed laterosphenoid, a laterosphenoid-prootic suture forming a blunt crest separating thesupratemporal fenestra into two fossae for muscular attachment, and the quadrateincompletely sutured to the braincase. Thus, these features characterize not only basal butderived Thalattosuchia, as suggested by previous authors. The main difference in theorbitotemporal region is that in the specimen described herein, and in the othermetriorhynchids examined, the trigeminal fossa is developed mainly caudal to thetrigeminal foramen, whereas in P. typus the fossa is developed rostral and caudal to thetrigeminal foramen. CT scanning indicates the presence of enlarged dorsal dural venoussinuses overlying the brain, as it has been described recently in Steneosaurus pictaviensis,and a well developed sinus within the quadrate. The large foramen ventrolateral to theoccipital condyle, which characterizes metriorhynchids, is confirmed as the entry for theinternal carotid artery.