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Dinosaur Scapulae and Forelimbs Resting Orientation

Ben Creisler

New in PLoS ONE:

Phil Senter & James H. Robins (2015)
Resting Orientations of Dinosaur Scapulae and Forelimbs: A Numerical
Analysis, with Implications for Reconstructions and Museum Mounts.
PLoS ONE 10(12): e0144036.

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.