Orientation of the pectoral girdle and forelimb posture in Neuquensaurus (Sauropoda, Titanosauria)

ALEJANDRO OTERO

Punta del Este, Uruguay

Congreso; 9th International Congress of Vertebrate Morphology; 2010

Society of Vertebrate Morphology

The reconstruction of the pectoral and forelimb musculoskeletal system of the titanosaur sauropod Neuquensaurus australis (Lydekker) is given herein. Soft tissue inferences and orientation of limb bones were based on the anatomy of extant crocodiles and birds, which both constitutes the Extant Phylogenetic Bracket of the preset study. Extant elephants were used as functional analogs for inferring the forelimb posture in sauropods because the columnar-graviportal arrangement of their limbs. When the glenoid fossa is oriented ventrally, the scapular blade of Neuquensaurus is inclined at an angle of 40º to the horizontal plane, which is much more inclined respect to other non-titanosaur sauropods. The crescent-shaped sternal plates are inferred to contact each other at the rib cage midline through a synchondrotic contact. The sternal-coracoid contact is given over the sternal anterolateral margins. Neuquensaurus does not present clavicles; however that structure has a primitive presence within Sauropodomorpha and is also present in one of the extant bracket taxa. Hence, a clavicular arrangement is given herein under two models: the “V” model, in which both clavicles contact each other at the midline of the rib cage; and the ‘non-bracing model’, where there is no contact of the clavicles. The scapular-coracoid contact determines a gleonid fossa of 90º which allows Neuquensaurus to a wide range of humeral protraction/retraction movements. The presence of a prominent olecranon process of the ulna, which is a reversal within Sauropoda, have permitted Neuquensaurus a wide range of flexion/extension movements respect to other sauropods.