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Re: Evolution of quadrupedalism in ornithischian dinosaurs



From: Ben Creisler
bcreisler@gmail.com

Here's a link to the press release from the Natural History Museum:


http://www.nhm.ac.uk/about-us/news/2012/june/muscle-reconstruction-reveals-how-dinosaurs-stood111815.html

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Susannah C. R. Maidment and Paul M. Barrett (2012)
Does morphological convergence imply functional similarity? A test
using the evolution of quadrupedalism in ornithischian dinosaurs.
Proceedings of the Royal Society B (advance online publication)
doi: 10.1098/rspb.2012.1040
http://rspb.royalsocietypublishing.org/content/early/2012/06/15/rspb.2012.1040.abstract




Convergent morphologies are thought to indicate functional similarity,
arising because of a limited number of evolutionary or developmental
pathways. Extant taxa displaying convergent morphologies are used as
analogues to assess function in extinct taxa with similar
characteristics. However, functional studies of extant taxa have shown
that functional similarity can arise from differing morphologies,
calling into question the paradigm that form and function are closely
related. We test the hypothesis that convergent skeletal morphology
indicates functional similarity in the fossil record using
ornithischian dinosaurs. The rare transition from bipedality to
quadrupedality occurred at least three times independently in this
clade, resulting in a suite of convergent osteological
characteristics. We use homology rather than analogy to provide an
independent line of evidence about function, reconstructing soft
tissues using the extant phylogenetic bracket and applying
biomechanical concepts to produce qualitative assessments of muscle
leverage. We also optimize character changes to investigate the
sequence of character acquisition. Different lineages of quadrupedal
ornithischian dinosaur stood and walked differently from each other,
falsifying the hypothesis that osteological convergence indicates
functional similarity. The acquisition of features correlated with
quadrupedalism generally occurs in the same order in each clade,
suggesting underlying developmental mechanisms that act as
evolutionary constraints.