Novel reconstruction of the orientation of the pectoral girdle in sauropods

Abstract

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 558 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 (60-658), Camarasaurus (60-658), and Opisthocoelicaudia (55-658). 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. Anat Rec, 290: 32-47, 2007. 2006

The Articulation of Sauropod Necks: Methodology and Mythology

“…Again, it is not sufficient to simply cite examples of this behavior in extant vertebrates to support the speculation that sauropods did as well. Osteological correlates, fortunately, have been identified in avian and crocodilian cervical and dorsal morphology [94], [117], [15], [46], [118], [119], [120] which allow an EPB-based inference that at least some sauropods suspended their necks in front of the body. It does not necessarily follow, however, that the neck were held in ONP.…”

“…But the modern interpretation of the pectoral girdles [cf. 32], [ 46] elevates the anterior dorsal column to approximately horizontal (Figure 6c, d), and this is naturally reflected in higher head heights. The ‘straight’ sauropod neck was subsequently reconstructed clearly horizontal or upward sloping, and when the less-than-avian 1999 estimates of diplodocid neck flexibility are applied to the revised bauplan, the 2005 studies [31]–[32] clearly showed that even the diplodocids could reach high enough that their feeding envelopes overlapped vertically with some other sympatric sauropod taxa regarded as ‘high browsers’.…”

“…Importantly, studies of sauropod forelimbs and pectoral girdles [32], [49], [50] is resulting in the reconstruction of diplodocids and camarasaurids as much taller at the shoulder [31]–[32], [46] than when first described [26], [37], [45] (Figure 6). With their anterior dorsal columns no longer depicted as steeply descending, but instead horizontal or slightly rising through the shoulders, their heads would rise accordingly, and consequently even ‘low browsers’ such as Diplodocus could have engaged in an ecospace that many would consider as ‘high browsing’ [32] – see Figure 7.…”

Osteology ofRebbachisaurus garasbaeLavocat, 1954, a diplodocoid (Dinosauria, Sauropoda) from the early Late Cretaceous–aged Kem Kem beds of southeastern Morocco

“…We hypothesize that the scapula was oriented in life such that the chord of the glenoid formed by the scapula and coracoid is approximately horizontal. See Wilhite (2005) and Schwarz et al (2007) for alternative interpretations.…”

Clavicles, interclavicles, gastralia, and sternal ribs in sauropod dinosaurs: new reports from Diplodocidae and their morphological, functional and evolutionary implications

“…; Schwarz et al. ,b; Remes, ). Putative clavicles are predicted to connect the scapulae dorsal to the coracoids but, until recently, no articulated pair had been reported in sauropods (Remes, ; but see Galiano & Albersdörfer, for an articulated specimen).…”