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Re: New references



Nitpicking, but Mickey and I disagree (what's new?) ...

Mickey Mortimer (Mickey_Mortimer111@msn.com) wrote:
 
<...Also, the maxillary "fenestra" is more of a fossa, as it does not
perforate the bone (besides the connection with the antorbital fenestra). 
Nor is it retained inside the antorbital fossa, as the interfenestral bar
is not recessed.>

  The left maxillary fenestra does penetrate the maxilla, however. It is
apparent in figures 9 and 10 that this is the case for both sides of the
skull, however that the lateral view of the right side seems to show a
smooth absence of fenestra. As described by Makovicky et al.: "The lateral
surface of the maxilla is perforated by two large, elongated antorbital
openings (figs. 2, 3). The maxillary fenestra is elliptical and extends
from below the external nares to the midway point between the
maxillary-premaxillary suture and the preorbital bar. This fenestra has an
osseous medial wall, which is perforated by a small hole in slightly
different positions on each side, but these holes may be weathering
artifacts. ... Anteriorly, the rostral end of the maxilla overhangs the
maxillary fenestra to form a large pocket." (pg. 7)

  It is this medial wall that Mickey apparently perceives as a continuous
surface of the maxillary wall, but it is a sharp-rimmed fenestra, and the
condition is corroborated in *Troodon formosus* by a personal
communication from Chris Brochu. That the condition is not apparent in
other taxa may be due to the absence of ossification of this medial wall
in other taxa. One sees extensive narial adaptations in *Pinacosaurus* and
oviraptorids, a condition possibly related to their desert environment,
and this would also seem to be an evolutionary feature in basal
troodontids. Without that medial wall, the fenestra would be said to be
fully perforated.

<Interestingly, the narial passage follows the top of the snout until it
exits on the anterodorsal corner of the antorbital fenestra, presumedly to
then curve ventrally through the posteriorly placed choanae.  This is much
like Paul's (2002) reconstruction of dromaeosaurids, but unlike the Oregon
team's endothermic reconstructions.>

  What is interesting is that the CT scanning shows TWO overlying
chambers, on of which is limited below by medial laminae from the maxilla
dorsal to the maxillary fenestrae and is continuous with the external
nares, and another below this, running above the maxillopalatine plate of
the secondary palate, also continuous with the external nares. One of
these presumably is the actual inspiratory nasal passage, but both may be
respiratory in function, as well as the "nasal" passage. Makovicky et al.
lable the dorsal one as the nasal chamber, and the ventral one as a
pneumatic chamber; both would be respiratory as in birds, in which both
are essentially pneumatic.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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