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Cranial anatomy of A. atokensis and its implications for the phylogeny of Allosauroidea

Dear DMLers,
a new interesting paper was published yesterday:

Eddy, D. R. & Clarke, J. A. 2011. New Information on the Cranial
Anatomy of Acrocanthosaurus atokensis and Its Implications for the
Phylogeny of Allosauroidea (Dinosauria: Theropoda). PLoS ONE 6(3):

Allosauroidea has a contentious taxonomic and systematic history.
Within this group of theropod dinosaurs, considerable debate has
surrounded the phylogenetic position of the large-bodied allosauroid
Acrocanthosaurus atokensis from the Lower Cretaceous Antlers Formation
of North America. Several prior analyses recover Acrocanthosaurus
atokensis as sister taxon to the smaller-bodied Allosaurus fragilis
known from North America and Europe, and others nest Acrocanthosaurus
atokensis within Carcharodontosauridae, a large-bodied group of
allosauroids that attained a cosmopolitan distribution during the
Early Cretaceous.

Methodology/Principal Findings
Re-evaluation of a well-preserved skull of Acrocanthosaurus atokensis
(NCSM 14345) provides new information regarding the palatal complex
and inner surfaces of the skull and mandible. Previously inaccessible
internal views and articular surfaces of nearly every element of the
skull are described. Twenty-four new morphological characters are
identified as variable in Allosauroidea, combined with 153 previously
published characters, and evaluated for eighteen terminal taxa.
Systematic analysis of this dataset recovers a single most
parsimonious topology placing Acrocanthosaurus atokensis as a member
of Allosauroidea, in agreement with several recent analyses that nest
the taxon well within Carcharodontosauridae.

A revised diagnosis of Acrocanthosaurus atokensis finds that the
species is distinguished by four primary characters, including:
presence of a knob on the lateral surangular shelf; enlarged posterior
surangular foramen; supraoccipital protruding as a double-boss
posterior to the nuchal crest; and pneumatic recess within the medial
surface of the quadrate. Furthermore, the recovered phylogeny more
closely agrees with the stratigraphic record than hypotheses that
place Acrocanthosaurus atokensis as more closely related to Allosaurus
fragilis. Fitch optimization of body size is also more consistent with
the placement of Acrocanthosaurus atokensis within a clade of larger
carcharodontosaurid taxa than with smaller-bodied taxa near the base
of Allosauroidea. This placement of Acrocanthosaurus atokensis
supports previous hypotheses of a global carcharodontosaurid radiation
during the Early Cretaceous.

It can be downloaded here: http://dx.doi.org/10.1371/journal.pone.0017932

Daniel Madzia
web: www.wildprehistory.org
mail: daniel.madzia@gmail.com
skype: danielmadzia