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Re: Caudipteryx: MY Perspectives on the Skull [was: Details on....]



Jaime Headden wrote-

>   The accessory fossa here may be the same foramen located in
> the maxilla in Oviraptoridae. *Avimimus*, *Chirostenotes*, and
> *Erlikosaurus* don't seem to have this.

I find the configuration in oviraptorids hard to judge.  The crestless
oviraptorid ZPAL MgD-I/95 has four maxillary foramina/fenestrae, two inside
the antorbital fossa and two outside.  The Oviraptor philoceratops holotype
has no maxillary fenestrae inside its antorbital fossa.  GI 100/42, referred
to O. philoceratops, has a large maxillary fenestra and one or perhaps two
small fossae outside the antorbital fossa.  Conchoraptor seem to have no
antorbital fenestra at all, just an antorbital fossa.  I'm sure much of this
variation is due to preservation and illustration, but I don't know which
configurations are correct at this point.  Also, how do you know about the
maxilla of Avimimus, when it is unknown?

>   The long posterior process does not indicate fusion of the
> prefrontal: the elements are separate (for instance) in
> ornithomimids with a long posterior ramus of the lachrymal.
> Dromaeosaurids vary, but the prefrontal is also very small and
> ovate, and the region in oviraptorids is problematic, because of
> extensive fusion of braincase elements may have carried over
> here. Also, supraorbital elements in troodontids, *Avimimus,*
> *Erlikosaurus,* and possibly also oviraptorids may be being
> confused with prefrontals.

You're right regarding the elongate posterior process not indicating the
lack of a prefrontal.  There is also no element preserved in any of the
skulls that could be a prefrontal though.  What's this about supraorbital
elements
in theropods?  Although Carpenter and Currie (2000) say that an extra
element is involved in the skull roof of Giganotosaurus, I thought that for
the most part supraorbitals were exclusive to ornithischians.

>   One reason why Ji et al's postobital is probably not a
> quadratojugal: lack of a postoventral process for the quadrate
> articulation.

I think either short process could be the posteroventral quadratojugal
process.  The problem I see is that what would be the jugal process is too
short.

>   Unfortunately, my biggest beef is with the quadrate. In BPM
> 0001, it can be observed that both quadrates are present, one of
> which is disarticulated and flipped so that the medial surface
> is exposed externally. This allows us to observed both an
> articulated quadrate with exposed head (IVPP V12430), and a
> disarticulated quadrate in medial view. The proximal expansion
> of the head can be observed separate from the medial [squamosal]
> head, and as such, would articulate not with the squamosal, but
> more dorsally and laterally, with the postorbital. The medial
> head can be observed in both quadrates and is well emarginated
> from the lateral margin of the bone. Thus, the head is
> bicephalic.

Which element do you identify as the other quadrate in BPM 0001?  I only see
one.  Also, I would hardly call the quadrate of IVPP 12430 articulated, as
it is shifted about 15 mm ventrally, a few mm posteriorly and rotated
posteroventrally.  Interesting observation regarding the quadrate heads
though.  Although dorsal portion is hidden in NGMC 97-9-A and I see nothing
suggesting two heads in IVPP V 12430, a close inspection of the plate of BPM
0001 suggests you may be correct.  However, the authors state only one head
is present, which leaves me with doubts.

>   The element appears correspond to the anterior palatine or to
> the ectopterygoids, as I see it. The taper of one end is
> possibly the palatinovomeral process, the broader expanded end
> being the maxillary contact.

In addition to the possibility of it being the anterior palatine, perhaps
it's the posterior section of a tetraradiate palatine.  I suppose the
ectopterygoid is also possible, but I think the C-shaped elements are
correctly identified as this.

>   These are present in IVPP V12430 and NGMC 97-9-A (very
> slightly) and look like the medial (maxillary) processes of the
> premaxillae, contacting the vomers between them. The secondary
> palate as reconstructed between them would then appear to be
> shorter than the length of the premaxillae.

Although I see no evidence of their existence in NGMC 97-9-A or IVPP V 12430
(unless you're talking about the processes extending from beneath the nasals
in the latter specimen, which wouldn't be plausible palatal premaxillary
processes at all), I agree that that is the most probable identification.
Good call Jaime.

>   This C-shaped element in preserved in both named specimens
> Mickey has cited. However, the element does not correspond to
> the morphology of any palatal element I have seen to date, and
> Zhou et al.'s identification seems to be based on the hook-like
> lateral process of the reptilian ectopterygoid.

I think the element in NGMC 97-9-A is extremely similar to the theropod
ectopterygoid.  Even comparing it to Allosaurus shows remarkable
similarities.  I'll scan you the figure of Allosaurus' ectopterygoid in
dorsal view from Madsen (1976) if you want.  Very similar.  The element in
IVPP V 12430
is not nearly as similar, but does resemble the element in NGMC 97-9-A.

>   More of the vomer? Delicate thing, you know, in most
> theropods: broad shallow head succeeded posteriorly by two long
> vertical lamina.

Perhaps.  If this is true, then the very slender element directly anterior
to the lacrimal may be a palatine process of the vomer.  Then again, it
could be part of the ectopterygoid.

> <The surangular and dentary may be fused in these specimens,?
>
>   Pardon? They look quite well separate and defined. The
> paratype and BMP 0001 have disarticulated dentaries, even.

The lack of sutures in some areas of the lower jaws in confusing.  The
dentary, surangular and angular look separate in NGMC 97-9-A.  Although the
posterior jaw may look fused, I think the angular may be missing
posteriorly.  In BPM 0001, there is no dentary-surangular suture either
dorsally or ventrally on the right mandible.  However, the left dentary is
disarticulated and there is no hint of a surangular-angular suture medially
on the right mandible.  In IVPP V 12430, there is no suture between the
surangular and angular or the posterodorsal dentrary process and the
surangular on the left mandible.  There are sutures between the
posteroventral dentary process and the surangular-angular however.  This
matches with the free posteroventral process on the right dentary.  The
element directly below the left surangular might look like an unfused
angular articulated to the surangular.  However, there is a small tubercle
visible on it that matches a tubercle on the medial angular of BPM 0001,
suggesting it is an angular in medial view.  It's unfortunate so many of
these fusions are ambiguous, as it could phylogenetic utility when compared
to caenagnathids.

Mickey Mortimer