Sphenosuchus acutus (Haughton 1915) Early Jurassic ~195 mya, ~1.4m in length, was the first of the quadrupedal crocodylomorphs. Sphenosuchus was derived from a sister to SMNS 12352 and phylogenetically preceded Saltoposuchus and Dibothrosuchus.
Distinct from Terrestrisuchus, the skull of Sphenosuchus was much smaller relative to the rest of the body. The jawline was deeper and ventrally convex with a premaxilla/maxilla kink. The antorbital fenestra was deeper than a slit. The squamosal shelf was downturned posteriorly. Anterior to the vomers the maxillae produce a medial shelf that includes a new premaxillary fenestration at the suture.
The neural spines were taller. The coracoid is stem-shaped, not disc-shaped as in more primitive taxa. Whereas in Cosesaurus the coracoid became stem-like at the onset of bipedalism, here it occurs at the return to quadrupedalism. The coracoid still slides. It is not socketed, as in fenestrasaurs/pterosaurs and birds.
The pubis is extremely elongated. The femur and tibia were similar in length to the humerus. |
