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Euoplocephalus internal cranial morphology (with videos)
From: Ben Creisler
A new online paper:
Tetsuto Miyashita, Victoria M. Arbour, Lawrence M. Witmer & Philip J.
The internal cranial morphology of an armoured dinosaur Euoplocephalus
corroborated by X-ray computed tomographic reconstruction.
Journal of Anatomy (advance online publication)
Internal cranial anatomy is a challenging area to study in fossilized
skulls because of small sample sizes and varied post-mortem preservational
alterations. This difficulty has led to the lack of correspondence between
results obtained from direct osteological observation and from more
indirect reconstruction methods. This paper presents corroborating evidence
from direct osteological observation and from reconstruction based on
computed X-ray tomography (CT) on the internal cranial anatomy of the
ankylosaurid dinosaur Euoplocephalus tutus. A remarkable specimen of
Euoplocephalus preserves rarely observed internal cranial structures such
as vascular impressions in the nasal cavity, olfactory turbinates and
possible impressions of conchae. Comparison with fossils and CT models of
other taxa and other Euoplocephalus specimens adds osteological evidence
for the previously reconstructed nasal cavity in this dinosaur and revises
the previously described braincase morphology. A new interpretation of the
ethmoidal homology identifies a mesethmoid, sphenethmoid and ectethmoid.
These ethmoidal ossifications are continuous with the mineralized walls of
the nasal cavity. The location of the olfactory fenestra provides further
evidence that the olfactory regions of the nasal cavity are pushed to the
sides of the main airway. This implies that the function of the vascular
impressions in the nasal cavity and the looping of the cavity are not
related to olfaction. A byproduct of the elongate, looping airway is a
dramatic increase in surface area of the nasal respiratory mucosa, which in
extant species has been linked to heat and water balance. A role in
vocalization as a resonating chamber is another possible function of the
looping and elongation of the nasal cavity. Olfaction remains as a possible
function for the enlarged olfactory region, suggesting that multiple
functions account for different parts of the ankylosaurid nasal cavity that
underwent substantial modification. Cranial endocasts show negligible
variation within Euoplocephalus, which lends some confidence to
interspecific comparisons of endocranial morphology.
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