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Quadrupedal dinosaur forearm posture and mobility

From: Ben Creisler

New in PLoS ONE:

Collin S. VanBuren & Matthew Bonnan (2013)
Forearm Posture and Mobility in Quadrupedal Dinosaurs.
PLoS ONE 8(9): e74842.

Quadrupedality evolved four independent times in dinosaurs; however,
the constraints associated with these transitions in limb anatomy and
function remain poorly understood, in particular the evolution of
forearm posture and rotational ability (i.e., active pronation and
supination). Results of previous qualitative studies are inconsistent,
likely due to an inability to quantitatively assess the likelihood of
their conclusions. We attempt to quantify antebrachial posture and
mobility using the radius bone because its morphology is distinct
between extant sprawled taxa with a limited active pronation ability
and parasagittal taxa that have an enhanced ability to actively
pronate the manus. We used a sliding semi-landmark, outline-based
geometric morphometric approach of the proximal radial head and a
measurement of the angle of curvature of the radius in a sample of 189
mammals, 49 dinosaurs, 35 squamates, 16 birds, and 5 crocodilians. Our
results of radial head morphology showed that quadrupedal
ceratopsians, bipedal non-hadrosaurid ornithopods, and theropods had
limited pronation/supination ability, and sauropodomorphs have unique
radial head morphology that likely allowed limited rotational ability.
However, the curvature of the radius showed that no dinosaurian clade
had the ability to cross the radius about the ulna, suggesting
parallel antebrachial elements for all quadrupedal dinosaurs. We
conclude that the bipedal origins of all quadrupedal dinosaur clades
could have allowed for greater disparity in forelimb posture than
previously appreciated, and future studies on dinosaur posture should
not limit their classifications to the overly simplistic extant