Abstract
The inclination of the scapular blade and the resting pose of the forelimb in dinosaurs differ among reconstructions and among skeletal mounts. For most dinosaurian taxa, no attempt has previously been made to quantify the correct resting positions of these elements. Here, we used data from skeletons preserved in articulation to quantify the resting orientations of the scapula and forelimb in dinosaurs. Specimens were included in the study only if they were preserved lying on their sides; for each specimen the angle between forelimb bones at a given joint was included in the analysis only if the joint was preserved in articulation. Using correlation analyses of the angles between the long axis of the sacrum, the first dorsal centrum, and the scapular blade in theropods and Eoraptor, we found that vertebral hyperextension does not influence scapular orientation in saurischians. Among examined taxa, the long axis of the scapular blade was found to be most horizontal in bipedal saurischians, most vertical in basal ornithopods, and intermediate in hadrosauroids. We found that in bipedal dinosaurs other than theropods with semilunate carpals, the resting orientation of the elbow is close to a right angle and the resting orientation of the wrist is such that the hand exhibits only slight ulnar deviation from the antebrachium. In theropods with semilunate carpals the elbow and wrist are more flexed at rest, with the elbow at a strongly acute angle and with the wrist approximately at a right angle. The results of our study have important implications for correct orientations of bones in reconstructions and skeletal mounts. Here, we provide recommendations on bone orientations based on our results.
Highlights
Interpretations of the resting positions of dinosaurian scapulae and forelimbs are inconsistent among museum mounts and illustrations
Even in dromaeosaurid and oviraptorosaurian theropods, which are often depicted with the scapular blade dorsal to the ribcage with its flat internal surface subhorizontal as in extant birds [4,5,6], specimens preserved in articulation show that the scapulae are instead oriented as in other dinosaurs [7,8,9,10,11,12] (Fig 1C)
That does not reveal the angle at which the long axis of the scapular blade was held with respect to the horizontal
Summary
Interpretations of the resting positions of dinosaurian scapulae and forelimbs are inconsistent among museum mounts and illustrations. Dinosaur skeletons that are preserved in articulation can be used as a first estimate of the resting poses of scapulae and forelimbs Such specimens show that the scapular blade is positioned along the sides of the ribcage with its flat internal surface subvertical and the glenoid facing ventrally (Figs 1, 2 and 3). Even in dromaeosaurid and oviraptorosaurian theropods, which are often depicted with the scapular blade dorsal to the ribcage with its flat internal surface subhorizontal as in extant birds [4,5,6], specimens preserved in articulation show that the scapulae are instead oriented as in other dinosaurs [7,8,9,10,11,12] (Fig 1C). That does not reveal the angle at which the long axis of the scapular blade was held with respect to the horizontal
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