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Basal ornithischian muscles and locomotion in new JVP



From: Ben Creisler
bh480@scn.org

The new issue (November 2011) of the Journal of Paleontology is available
online. 

http://www.tandfonline.com/toc/ujvp20/current

There are number of articles about archosaurs and archosauromorphs, but
only one strictly about dinosaurs:


Susannah C. R. Maidment & Paul M. Barrett (2011)
The locomotor musculature of basal ornithischian dinosaurs.
Journal of Vertebrate Paleontology 31(6):, 1265-1291
DOI:10.1080/02724634.2011.606857
http://www.tandfonline.com/doi/abs/10.1080/02724634.2011.606857

The earliest ornithischian dinosaurs were small bipeds that possessed the
derived, retroverted pubis that is synapomorphic for the clade. Their
forelimbs were modified for grasping. Subsequently, ornithischians radiated
into numerous body shapes and sizes. Three lineages independently evolved
large size and quadrupedality, requiring profound changes to the osteology
and myology of the locomotor apparatus. Using comparisons with extinct
archosaurian outgroups, as well as extant birds and crocodilians, we
reconstruct basal ornithischian limb musculature in order to determine the
sequence of musculoskeletal changes that occurred prior to and during the
early evolution of Ornithischia. The musculoskeletal anatomy of basal
ornithischian forelimbs was probably more similar to that of the crown
group archosaur common ancestor and crocodilians than it was to birds.
Reduction or loss of the clavicle resulted in migration of the clavicular
deltoid onto the proximal scapula and development of a distinct acromial
process. The coracobrachialis brevis and supracoracoideus probably
protracted the humerus, whereas the scapulohumeralis caudalis and
deltoideus scapularis probably retracted it. The deltoideus clavicularis
was likely a humeral abductor. In the hind limb, the elongate preacetabular
process indicates lateral migration of important femoral protractors to the
ilium from an inferred ancestral location on the dorsal vertebrae. The
puboischiofemoralis externus was greatly reduced or possibly lost due to
pubic retroversion. The reconstruction of basal ornithischian myology
provides a baseline for determining the musculoskeletal changes associated
with different locomotor modes in ornithischians, and a foundation for
biomechanical studies of dinosaur locomotion.



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