Sauropod shoulders

[Guy Leahy <xrciseguy@sbcglobal.net>]

Anat Rec (Hoboken). 2007 Jan;290(1):32-47.

Novel reconstruction of the orientation of the
pectoral girdle in sauropods.Schwarz D, Frey E, Meyer
CA. 
Naturhistorisches Museum Basel, Basel, Switzerland.
daniela.schwarz@bs.ch

The orientation of the scapulocoracoid in sauropod
dinosaurs is reconstructed based on comparative
anatomical investigations of pectoral girdles of
extant amniotes. In the reconstruction proposed here,
the scapula of sauropods stands at an angle of at
least 55 degrees to the horizontal plane in mechanical
coherence with the sternal apparatus including the
coracoids. The coracoids are oriented cranioventrally
to the rib cage and the glenoid is directed
mediolaterally, which allows the humerus to swing in a
sagittal plane. The inclination of the scapula to the
horizontal plane is reconstructed for Diplodocus
(60-65 degrees), Camarasaurus (60-65 degrees), and
Opisthocoelicaudia (55-65 degrees). The inclination of
the scapulocoracoid has consequences for the overall
body posture in Camarasaurus and Opisthocoelicaudia,
where the dorsal contour would have ventrally declined
toward the sacrum. Scapulocoracoid mobility depends on
the arrangement of clavicles, the reconstruction of a
coracosternal joint, and the reconstructed musculature
of the shoulder girdle. In a crocodylian model of the
shoulder musculature, m. serratus profundus and
superficialis form a muscular sling, which suspends
the trunk from the shoulder girdle and would allow a
certain mobility of the scapulocoracoid. An avian
model of the shoulder musculature would also mean
suspension by means of the m. serratus complex, but
indicates a closer connection of the scapula to the
dorsal ribs, which would lead to more restricted
movements of the scapulocoracoid in sauropods.