Saurosuchus galilei Reig, 1959

Nesbitt, Sterling J., 2011, The Early Evolution Of Archosaurs: Relationships And The Origin Of Major Clades, Bulletin of the American Museum of Natural History 2011 (352), pp. 1-292 : 33-35

Saurosuchus galilei Reig, 1959 (fig. 11D–E)

AGE: Late Carnian, Late Triassic ( Rogers et al., 1993, adjusted for the new Triassic timescale of Muttoni et al., 2004).

OCCURRENCE: Ischigualasto Formation, Argentina.

HOLOTYPE: PVL 2062, nearly complete skull, posteriormost portion missing.

REFERRED MATERIAL: PVL 2198, partial maxilla, left ilium, both ischia, nine articulated dorsal vertebrae and fragments, part of the dermal armor, associated ribs and teeth; PVL 2557, two dorsal vertebrae, both sacrals, nine caudal vertebrae, right ilium and ischium, partial pubis, parts of right femur, tibia, fibula, complete right tarsus and foot, associated ribs and chevrons; PVSJ 32, skull and partial skeleton.

REMARKS: Saurosuchus galilei was named from a nearly complete skull ( Reig, 1959) from the Ischigualasto Formation, and isolated material from this unit has been referred to the taxon since ( Sill, 1974). The holotype represented the first relatively complete skull material of any rauisuchian to date and stands as one of the most complete skulls of a ‘‘rauisuchian.’’ Of all the specimens referred to the taxon, only PVSJ 32, a complete skull and presacral vertebral column, can be confidently assigned to Saurosuchus galilei because all the autapomorphies of the taxon lie in the skull (see Alcober, 2000). Most of the isolated postcranial material from the Ischigualasto Formation was assigned to Saurosuchus without much explanation. Moreover, at least one other large paracrocodylomorph, Sillosuchus , is known from the Ischigualasto Formation. The absence of a coherent, supported assignment of the isolated material to Saurosuchus has led to confusion. For example, the cervical vertebra (PVL 2472) assigned to Saurosuchus belongs to a gigantic specimen of Sillosuchus (see above). Furthermore, there are proportional differences between the metatarsals of two pedes (PVL 2557 and PVL 2267) assigned to Saurosuchus . Moreover, metatarsal V of PVL 2557 is short and possesses a clear facet for articulation with a phalanx, whereas PVL 2267 possesses a long, tapered metatarsal V without a clear facet for articulation with a phalanx. The ilium found with PVL 2267 shares synapomorphies (e.g., elongated preacetabular process, concave ischial peduncle) with Sillosuchus and other poposauroids. Interestingly, the specimens that are possibly referable to Sillosuchus , along with the holotype of the taxon, are found in the lowest one-third of the Ischigualasto Formation ( Sill, 1974; Alcober and Parrish, 1997), whereas Saurosuchus is from the upper two-thirds of the formation. The following examples demonstrate that all the material assigned to Saurosuchus may not belong to the taxon. Therefore, I score the cranial material, osteoderm, and axial column from the holotype (PVL 2062) and PVSJ 32 and score a few additional characters from PVL 2198 and the hind limb of PVL 2557.

Saurosuchus was only recently utilized in explicit phylogenetic analyses. It was found closely related to Prestosuchus and Ticinosuchus by Parrish (1993) and Benton (2004) and to lie outside a clade containing Postosuchus kirkpatricki , Tikisuchus , Batrachotomus , aetosaurs, and crocodylomorphs by Gower and Walker (2002) based on braincase characters. In all analyses, Saurosuchus was found as a crocodylian-line archosaur.

The following autapomorphies listed by Alcober (2000) are accepted here: sculptured skull roof and maxilla; ventral process of the lacrimal forms a slender pillar that abuts the jugal laterally; development of a crista on the dorsal supraoccipital; development of a robust, laterally expanded, capitate process of the laterosphenoid.

Alcober (2000) also listed three autapomorphies focused on the frontal and surrounding bones (reduced postfrontal hidden in dorsal view, thickening of the border of the frontal at the level of the orbital fenestra, and presence of a lateral process of the posterolateral frontal). All three of these characters are not unique among crocodylian-line archosaurs once the large bone dorsal to the orbit is reidentified as a palpebral fused to the frontal. A similar frontal-palpebral relationship is found in Postosuchus kirkpatricki (TTU-P 9000) and Polonosuchus silesiacus (ZPAL Ab III/563).

KEY REFERENCES: Reig, 1959; Sill, 1974; Alcober, 2000.