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Alligator forelimb walking kinematics

From: Ben Creisler

A recent non-dino paper that may be of interest:

David B. Baier & Stephen M. Gatesy (2013)
Three-dimensional skeletal kinematics of the shoulder girdle and
forelimb in walking Alligator.
Journal of Anatomy (advance online publication)
DOI: 10.1111/joa.12102

Crocodylians occupy a key phylogenetic position for investigations of
archosaur locomotor evolution. Compared to the well-studied hindlimb,
relatively little is known about the skeletal movements and mechanics
of the forelimb. In this study, we employed manual markerless XROMM
(X-ray Reconstruction Of Moving Morphology) to measure detailed 3-D
kinematics of the shoulder girdle and forelimb bones of American
alligators (Alligator mississippiensis) walking on a treadmill.
Digital models of the interclavicle, scapulocoracoid, humerus, radius
and ulna were created using a 3-D laser scanner. Models were
articulated and aligned to simultaneously recorded frames of
fluoroscopic and standard light video to reconstruct and measure joint
motion. Joint coordinate systems were established for the
coracosternal, glenohumeral and elbow joints. Our analysis revealed
that the limb joints only account for about half of fore/aft limb
excursion; the remaining excursion results from shoulder girdle
movements and lateral bending of the vertebral column. Considerable
motion of each scapulocoracoid relative to the vertebral column is
consistent with coracosternal mobility. The hemisellar design of the
glenohumeral joint permits some additional translation, or sliding in
the fore-aft plane, but this movement does not have much of an effect
on the distal excursion of the bone.