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Ornithischian dinosaur locomotion with 3-D computational modeling

From: Ben Creisler

A new online paper:

Susannah C. R. Maidment, Karl T. Bates, Peter L. Falkingham, Collin
VanBuren, Victoria Arbour and Paul M. Barrett (2013)
Locomotion in ornithischian dinosaurs: an assessment using
three-dimensional computational modelling.
Biological Reviews (advance online publication)
DOI:  10.1111/brv.12071

Ornithischian dinosaurs were primitively bipedal with forelimbs
modified for grasping, but quadrupedalism evolved in the clade on at
least three occasions independently. Outside of Ornithischia,
quadrupedality from bipedal ancestors has only evolved on two other
occasions, making this one of the rarest locomotory transitions in
tetrapod evolutionary history. The osteological and myological changes
associated with these transitions have only recently been documented,
and the biomechanical consequences of these changes remain to be
examined. Here, we review previous approaches to understanding
locomotion in extinct animals, which can be broadly split into
form–function approaches using analogy based on extant animals,
limb-bone scaling, and computational approaches. We then carry out the
first systematic attempt to quantify changes in locomotor muscle
function in bipedal and quadrupedal ornithischian dinosaurs. Using
three-dimensional computational modelling of the major pelvic
locomotor muscle moment arms, we examine similarities and differences
among individual taxa, between quadrupedal and bipedal taxa, and among
taxa representing the three major ornithischian lineages (Thyreophora,
Ornithopoda, Marginocephalia). Our results suggest that the ceratopsid
Chasmosaurus and the ornithopod Hypsilophodon have relatively low
moment arms for most muscles and most functions, perhaps suggesting
poor locomotor performance in these taxa. Quadrupeds have higher
abductor moment arms than bipeds, which we suggest is due to the
overall wider bodies of the quadrupeds modelled. A peak in extensor
moment arms at more extended hip angles and lower medial rotator
moment arms in quadrupeds than in bipeds may be due to a more columnar
hindlimb and loss of medial rotation as a form of lateral limb support
in quadrupeds. We are not able to identify trends in moment arm
evolution across Ornithischia as a whole, suggesting that the bipedal
ancestry of ornithischians did not constrain the development of
quadrupedal locomotion via a limited number of functional pathways.
Functional anatomy appears to have had a greater effect on moment arms
than phylogeny, and the differences identified between individual taxa
and individual clades may relate to differences in locomotor
performance required for living in different environments or for
clade-specific behaviours.