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Tawa (theropod from Late Triassic of New Mexico) forelimb myology

Ben Creisler

A new online paper:

Sara H. Burch (2014)
Complete forelimb myology of the basal theropod dinosaur Tawa hallae
based on a novel robust muscle reconstruction method.
Journal of Anatomy (advance online publication)
DOI: 10.1111/joa.12216

The forelimbs of nonavian theropod dinosaurs have been the subject of
considerable study and speculation due to their varied morphology and
role in the evolution of flight. Although many studies on the
functional morphology of a limb require an understanding of its
musculature, comparatively little is known about the forelimb myology
of theropods and other bipedal dinosaurs. Previous phylogenetically
based myological reconstructions have been limited to the shoulder,
restricting their utility in analyses of whole-limb function. The
antebrachial and manual musculature in particular have remained
largely unstudied due to uncertain muscular homologies in archosaurs.
Through analysis of the musculature of extant taxa in a robust
statistical framework, this study presents new hypotheses of homology
for the distal limb musculature of archosaurs and provides the first
complete reconstruction of dinosaurian forelimb musculature, including
the antebrachial and intrinsic manual muscles. Data on the forelimb
myology of a broad sample of extant birds, crocodylians, lizards, and
turtles were analyzed using maximum likelihood ancestral state
reconstruction and examined together with the osteology of the early
theropod Tawa hallae from the Late Triassic of New Mexico to formulate
a complete plesiomorphic myology for the theropod forelimb.
Comparisons with previous reconstructions show that the shoulder
musculature of basal theropods is more similar to that of basal
ornithischians and sauropodomorphs than to that of dromaeosaurids.
Greater development of the supracoracoideus and deltoideus musculature
in theropods over other bipedal dinosaurs correlates with stronger
movements of the forelimb at the shoulder and an emphasis on
apprehension of relatively large prey. This emphasis is further
supported by the morphology of the antebrachium and the intrinsic
manual musculature, which exhibit a high degree of excursion and a
robust morphology well-suited for powerful digital flexion. The
forelimb myology of Tawa established here helps infer the ancestral
conformation of the forelimb musculature and the osteological
correlates of major muscle groups in early theropods. These data are
critical for investigations addressing questions relating to the
evolution of specialized forelimb function across Theropoda.