Saurosuchus galilei (Alcober, 2000)

Gower, David J., 2002, Braincase evolution in suchian archosaurs (Reptilia: Diapsida): evidence from the rauisuchian Batrachotomus kupferzellensis, Zoological Journal of the Linnean Society 136 (1), pp. 49-76 : 64

SAUROSUCHUS GALILEI

Saurosuchus galilei Reig is known from the Upper Triassic Ischigualasto Formation of Argentina. Braincase elements were not among the original material described by Reig (1959) or in two subsequent descriptive accounts ( Reig, 1961; Sill, 1974), but a good and largely complete braincase was preserved in the specimen figured and described in detail by Alcober (2000). In overall form, the braincase of S. galilei resembles that of B. kupferzellensis rather more than that of the rauisuchians Postosuchus kirkpatricki and Tikisuchus romeri , in that the parabasisphenoid is fairly short from its dorsal to ventral edges (plesiomorphic condition). S. galilei braincase characters that are plesiomorphic for crown-group archosaurs include the absence of a semilunar depression and parabasisphenoid intertuberal plate, a lateral position on the parabasisphenoid for the entrance of the cerebral branch of the internal carotid artery, and a metotic foramen (i.e. an undivided metotic fissure). The lateral edge of the exoccipital bears a subvertical ridge, but this is not as prominent as in B. kupferzellensis . This ridge lies posterior to the single external foramen for the hypoglossal nerve, and there is some indication (left side of Alcober’s fig. 7A) that it extends down onto the dorsal part of the basioccipital. The posterior surface of the braincase shows a large unossified gap between the basal tuber of the basioccipital, ventral ridge of the opisthotic, and parabasisphenoid. The opposite exoccipitals and prootics meet along the midline. The pila antotica was ossified by prootic and parabasisphenoid, so that there is no contact between laterosphenoid and parabasisphenoid. Alcober’s fig. 8 shows that the base of the cultriform process of the parabasisphenoid bears a groove on its lateral surface, in an equivalent position to that described for B. kupferzellensis and interpreted as indicating the route of the palatine branch of the facial nerve and perhaps the palatine artery.

Alcober identified the presence of a ‘presphenoid’ in S. galilei , articulating with the laterosphenoid and prootic anterior to the single undivided opening for the middle cerebral vein and trigeminal nerve. Indeed, the limits of this element were identified as including a border to the trigeminal opening. Examination of Alcober’s figures shows the ‘presphenoid’ to be in a position occupied by the anteroventral portion of the laterosphenoid in a wide range of other Triassic archosaurs. Thus the suture between laterosphenoid and ‘presphenoid’ might alternatively represent a break in the (incomplete) posterior portion of laterosphenoid, extending from a potential zone of weakness at the trigeminal foramen. Fractures in this position have been observed in some Triassic archosaurs, but the pattern described by Alcober is consistent on both sides of the specimen, and I have not examined the material first hand.