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



Mickey_Mortimer (Mickey_Mortimer@email.msn.com) wrote:

<A single maxillary fenestra is present; there does not seem to
be much of an antorbital fossa.>

  In fact, the antorbital fossa (everything from the margin of
the fenestra forward to the lateral surface of the maxilla) is
longer than 50% of the maxillary length. Only one antorbital
fenestra, but this is like birds, oviraptorosaurs (not
corroborated in *Chirostenotes*, possible absence there), and
some other odds and ends (pardon me, I'm away from my
references, right now).

<BPM 0001 and IVPP V 12430 have an elongate anterior portion
with a pneumatic fossa, while NGMC 97-9-A is blunt anteriorly
without accessory fossae.>

  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.

<The lacrimal is triradiate, with an elongate posterior process,
suggesting the prefrontal is fused to it.>

  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. The entire orbital rim in *Troodon
formosus*, for instance, in comprised on a single element;
rather than propose this is a prefrontal, which may be fused to
the lachyrmal, this can merely be identified as a "supraorbital
element" that may correspond to an os palpedrale, os
supraorbitale, or os prefrontale. This is a region of theropod
anatomy that should be investigated: I cannot find much in the
literature regarding this, despite extensive works on
maniraptoriforms and carnosaurs that I've been reading lately.

<There is a large pneumatic lacrimal foramen, but no rugosities
or horns are evident.>

  Or lachrymal canal.

<The triradiate postorbital is much larger in BPM 0001 and IVPP
V 12430 than in NGMC 97-9-A.>

  As Mickey suggests later, the element proposed by Ji et al. as
the postorbital in the paratype (NGMC 97-9-A) is not a
postorbital (it looked like a jugal to me, at first) but
possibly corresponds to a palatal bone, in this case the only
element that migh bifurcate in that manner is a pterygoid
contact on the palatine (concave and deep in *Avimimus* and
oviraptorids, hence the identification), or an ectopterygoid.

<The squamosal is also poorly preserved, but has an elongate
tapered ventral process and a hooked posterior process that
exposes the quadrate head laterally.>

  The morphology of the squamosal seems to be similar in both
*Avimimus* and *Caudipteryx.* The squamosal, however, almost
nearly always covers the proximal end of the quadrate,
suggesting (first off) that the element in eroded. Investigation
may reveal fracture or erosion ... or not.

<The quadratojugal is not triradiate and has a dorsal process
more elongate than the anterior process.>

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

<The quadrate is single-headed, with a gently concave posterior
margin and a deep notch ventrally.  It is vertical and not
pneumatic.>

  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. 

<The braincase is visible in BPM 0001 and NGMC 97-9-A, but shows
no details besides several large foramina.>

  Unfortunately, no fractures can be clearly distinguished as
intra-elemental sutures, but this may also suggest the braincase
was fully fused, as is seen in birds, and partly in
*Archaeopteryx,* oviraptorids, *Erlikosaurus,* and
*Chirostenotes*.

<The broad posterior portion of the pterygoid is preserved in
BPM 0001, contacting the quadrate.  Another similar element is
unidentified in IVPP V 12430.  An L-shaped element, tapered on
one end and slightly expanded on the other, is identified as a
possible pterygoid in IVPP V 12430.  I can't see how this can be
a pterygoid (although my grasp of three-dimensional palates is
poor) and think it resembles a quadratojugal more.>

  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 BPM 0001, there are two pointed elements projecting
posterodorsally from the anteroventral margin of the external
naris that Zhou et al. identify as vomers.  If that is true,
they are very short compared to other theropods, as they extend
only halfway past the external nares.>

  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.

<A thin, C-shaped element in IVPP V 12430 is identified as an
ectopterygoid.  This is dissimilar from both the dumb-bell
shaped ectopterygoids of oviraptorids or the hook-shaped ones of
most theropods, although it is most similar to the latter.  The
ectopterygoid of NGMC 97-9-A is more robust, with the usual
thickened portion seen in most theropods.>

  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. 

<Several other cranial elements are also difficult to identify. 
Two elongate elements preserved in the snout of IVPP V 12430
could be vomers or vomeral processes of the palatines.>

  The latter is my bet, unless they are very strange
ceratobranchials and the other element of the hyoid is an
ossified ceratohyal....

<A vertical strap-like element, wider than the lacrimal and
found in the antorbital fenestra, defies identification but is
present in all three specimens.>

  Vomer?

<A small element in the naris of BPM 0001 is very similar to a
coronoid, but its position makes this identification suspect.>

  More of the vomer? Delicate thing, you know, in most
theropods: broad shallow head succeeded posteriorly by two long
vertical lamina. Proximally, they form a single, shallow lamina
that tapers to the head. The fusion of the posterior (pterygoid)
processes will cause this to occur much more caudally, as well.
 
<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.

<A ventral surangular process crosses the external mandibular
fenestra in BPM 0001 and extends partway into it in NGMC 97-9-A,
but not in IVPP V 12430.>

  This appears to be a small ventral portion of the this
blade-like bones in the upper cavity of the skull, and in the
bones themselves, I can't see this process being part of the
surangular ... it is not present in the type, paratype, or other
dentaries besides the one (IVPP V12430) that Zhou et al identify
it in.

[...]

  Regarding medial mandibular bones:

  both splenial and prearticular appear to be present, in some
cases loose from the dentary, and both are long and shallow, not
dorsally expanded. This is in keeping with the morphology of the
jaw in caenagnathoids.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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