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Re: Rauhut's Thesis
Mickey Mortimer (Mickey_mortimer11@msn.com) wrote (citing
Rauhut's 2000 PhD thesis):
<<Seven additional synapomorphies were found (premaxillary body
in front of external nares longer than body below the nares, and
angle between anterior margin of the premaxilla and alveolar
margin less than 70 degrees; presence of a constriction between
the articulated premaxillaries and maxillaries;>>
David Marjanovic (email@example.com) wrote:
<Are these three related to the subnarial gap?>
Only one: "presence of a constriction between the articulated
premaxillaries and maxillaries"; the first is a matter of
premaxillary elongation or narial retraction, the second is what
is called the "premaxillary angle" (Kirkland et al., 1993:
Hunteria 2(4), *Utahraptor*) and can be of phylogenetic
importance, but I feel that this is more a functional character
than anything else, certainly related to the length of the first
tooth, and extent of the roots or their orientation.
Please also note that the subnarial gap in coelophysids +
*Dilophosaurus* and *Liliensternus* is different than the gap in
spinosaurids, in the essential arrangement of the three
principle bones: maxilla, premaxilla, and vomers. In the
non-tetanurans, the premaxillae send small caudal processes
between the maxillae, and are constricted as such, as well as
this process being turned dorsally at the premaxillomaxillary
contact; the vomers insert as a small set of flanges at this
point, but form a distinct unit different from the rest of the
snout; the contact is not firmly set, and has led Welles (1976,
1984) and later Welles & Madsen (2000) to surmise that
*Dilophosaurus* had a mobile premaxilla, which is certainly
possible, though in agreement with Rowe (1989) I would say that
the mobile premaxilla does not make the jaw "weak" but can in
fact imply great structural capability.
In spinosaurids, the vomers and maxillae form a pair of
tightly appressed (no slot between them) rods that extend below
the premaxilla, and the premaxillae do not have the caudal
processes insert between the maxillae, but dorsal to them, and
all spinosaurid snouts known have at least two interdigitating
prongs that match up to slots and quite firmly lock the
premaxilla to the snout.
<I've often seen "no fanglike teeth in the dentary" used as an
apomorphy of Tetanurae, implying that their presence is
plesiomorphic. Where does this attitude come from?>
The enlarged third dentary tooth is a archosaur thing, among
other taxa, which some taxa loose. Many tetanurans often have
larger proximal teeth, with the third as big as the second, or
smaller than the second or third, or subequal in size with its
neighbors, but not larger.
<I can't judge that, but these characters sound pretty weak,
<<cervical vertebrae strongly opisthocoelous;>>
<Would this add rigidity or flexibility?>
Flexibility. Stiffer dorsal series in coelurosaurs and even
further rigidification of the trunk as we get closer to birds
parallels the avian respiration hypothesis of airsacs, etc.
<This sounds a lot like PDW (where Yangchuanosaurus was lumped
Yah, but while it is possible *Yangchuanosaurus* is synonymous
with *Metriacanthosaurus,* as Paul surmised, there are enough
reasons to retain the two species of *Sinraptor* as distinct,
and they themselves distinct from the one valid species of
*Yangchuanosaurus* (*Y. shangyouensis*, as *Y. magnus* appears
to be a mature individual of the first species).
<I'm already waiting that Dryptosaurus becomes a ceratosaur...>
I hope you're joking....
Jaime A. Headden
Where the Wind Comes Sweeping Down the Pampas!!!!
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