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Caudipteryx: My Reflections on the Postcranium [was: Details on....]



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

<An element labeled "?" by Zhou et al. located behind the skull
of IVPP V 12430 looks like an atlantal neurapophysis to me.>

  It is my understanding (forgive me if I've missed a form or
other that defies thisw morphology) but that when the atlas is
fused into a neural arch, the neural spine is never larger than
about 10% the length of the neurapophysis, in reptiles (sensu
stricto), even birds. This suggests that the pair of trapezoidal
neural spines pertain to the axis and third cervical neural
arches.

<There are five sacral vertebrae, unfused in IVPP V 12344.>

  Not in a single specimen, even those with disarticulated ilia,
do the sacra show up well. You get one or two that are exposed,
but that's it. Those exposed have centra with strongly expanded
epiphyses, and no pleurocoels. The neural arches are not fused
to the centra that I see. Furthermore, the centra seem to form
more or less a strait line from the first to the last, as
suggetsed by the lack of bevelling of the faces in exposed
centra.

<The last chevron is after the seventeenth caudal. 
Dorsoventrally elongate chevrons are present until after the
tenth caudal, all but the first are distally expanded.  No
dromaeosaur-like highly elongated prezygopophyses or chevrons
are present.>

  One thing I noted is that the type and paratype (NGMC 97-4-A
and 97-9-A, respectively) and the type of *C. dongi* (IVPP V
12344) have slender distal chevrons that are seldom
craniocaudally longer than they are deep, yet in BPM 0001 and
IVPP V 12430, they resemble the condition in *Nomingia,* where
they are shallower, longer craniocaudally, and resemble the
ventral blade that Barsbold et al., (2000a, b) describe.

<The glenoid seems to point mostly posteroventrally.>

  In the refered specimens, the coracoid forms a deep, nearly
90deg angle with the scapula. However, this angle appears to me
to be artificial, rather than actual, as most of the
scapulocoracoid suture on the scapula is exposed, but the
morphology of the coracoid suggests that it resembled the
condition in *Deinonychus* instead, and was shallowly angled,
perhaps only 20degs down from the dorsal margin. This makes the
glenoid face mostly ventrally, and correcting for the curved of
the ribs, a little laterally. I do, however, note that there
seems to be a slight recess between the elements on the dorsal
margin where the projecting acromion would overlie a small
pseudo- triosseal canal, much less derived than the condition in
*Velociraptor* (Norell and Makovicky, 1999)

<The carpus consists of a large semilunate, triangular radiale
and small rounded ulnare.>

  In addition, the type, and most refered specimens preserve a
small bone proximal to the third metacarpal which is insent from
the second metacarpal proximally, which would correspond to the
distal carpal III. I advocate a four-carpal manus, but this
element does not seem to offer any mechanical assistance.

<The ilium ...> 

  ... also appears to bear several striations and logitudinal
ridges on its lateral surface, as does *Microvenator.* These
ridges are present on _all_ specimens.

<The pubis is nearly straight and has an anterior foot much
larger than the posterior.>

  Well, I'd say slightly curved, concave cranially, but that's
my eye!

=====
Jaime A. Headden

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

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