Appendicular skeleton of Simosuchus clarki (Crocodyliformes: Notosuchia) from the Late Cretaceous of Madagascar

Abstract

ABSTRACT The notosuchian crocodyliform Simosuchus clarki from the Late Cretaceous of Madagascar, originally known from a single specimen preserving primarily the skull, lower jaw, and anterior postcranial skeleton, is now known from three additional partial skeletons that collectively preserve nearly the entire appendicular skeleton. Although typically crocodyliform in overall morphology, the appendicular skeleton of Simosuchus preserves a number of derived features of phylogenetic and functional significance. Notable features of the pectoral girdle and forelimb include an anteroposteriorly broad, tripartite scapular blade; a laterally directed scapular prominence; a proximally expanded humerus with a shallow deltopectoral crest; a distinct, semi-ellipsoidal glenohumeral condyle; a tightly articulating radius and ulna; and a relatively foreshortened manus with robust distal unguals. Notable features of the pelvic girdle and hind limb include a distinct, spur-like projection of the anterior process of the ischium; a femur with a distinctive anterior flange; and a relatively foreshortened pes. Generally, characteristics of the appendicular skeleton are consistent with a terrestrial lifestyle and provide insight into the behavior and locomotion of Simosuchus. The robust limb morphology observed in Simosuchus, together with expanded areas for insertion of pectoral and pelvic musculature in the proximal humerus and femur, is consistent with non-cursorial terrestrial locomotion in a relatively stout-bodied crocodyliform. Characteristics of the hind limb indicate a primarily semi-erect posture, in contrast to the erect posture inferred for other notosuchians.