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Reversions to quadrupedality in ornithischian dinosaurs
A new online paper:
Susannah C. R. Maidment, Donald M. Henderson & Paul M. Barrett (2014)
What drove reversions to quadrupedality in ornithischian dinosaurs?
Testing hypotheses using centre of mass modelling.
Naturwissenschaften (advance online publication)
The exceptionally rare transition to quadrupedalism from bipedal
ancestors occurred on three independent occasions in ornithischian
dinosaurs. The possible driving forces behind these transitions remain
elusive, but several hypotheses—including the development of dermal
armour and the expansion of head size and cranial ornamentation—have
been proposed to account for this major shift in stance. We modelled
the position of the centre of mass (CoM) in several exemplar
ornithischian taxa and demonstrate that the anterior shifts in CoM
position associated with the development of an enlarged skull
ornamented with horns and frills for display/defence may have been one
of the drivers promoting ceratopsian quadrupedality. A posterior shift
in CoM position coincident with the development of extensive dermal
armour in thyreophorans demonstrates this cannot have been a primary
causative mechanism for quadrupedality in this clade. Quadrupedalism
developed in response to different selective pressures in each
ornithischian lineage, indicating different evolutionary pathways to
convergent quadrupedal morphology.