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Alioramus braincase in PLoS ONE



From: Ben Creisler
bh480@scn.org

New in PLoS ONE (free pdf):

Bever, G.S., Brusatte, S.L., Balanoff, A.M., & Norell, M.A. (2011) 
Variation, Variability, and the Origin of the Avian Endocranium: Insights
from the Anatomy of Alioramus altai (Theropoda: Tyrannosauroidea). 
PLoS ONE 6(8): e23393. 
doi:10.1371/journal.pone.0023393
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0023393

The internal braincase anatomy of the holotype of Alioramus altai, a
relatively small-bodied tyrannosauroid from the Late Cretaceous of
Mongolia, was studied using high-resolution computed tomography. A number
of derived characters strengthen the diagnosis of this taxon as both a
tyrannosauroid and a unique, new species (e.g., endocranial position of the
gasserian ganglion, internal ramification of the facial nerve). Also
present are features intermediate between the basal theropod and avialan
conditions that optimize as the ancestral condition for Coelurosauria?a
diverse group of derived theropods that includes modern birds. The
expression of several primitive theropod features as derived character
states within Tyrannosauroidea establishes previously unrecognized
evolutionary complexity and morphological plasticity at the base of
Coelurosauria. It also demonstrates the critical role heterochrony may have
played in driving patterns of endocranial variability within the group and
potentially reveals stages in the evolution of neuroanatomical development
that could not be inferred based solely on developmental observations of
the major archosaurian crown clades. We discuss the integration of
paleontology with variability studies, especially as applied to the nature
of morphological transformations along the phylogenetically long branches
that tend to separate the crown clades of major vertebrate groups.


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