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Pleurocoels in Some Maniraptoriforms



I wrote:

<<Sacral pleurocoels are known in many
maniraptoriformes, and full sacral pluerocoely is
described only in caenagnathids (Sues, 1998) and
*Ornithodesmus*? [I cannot recall, and the relevant
paper has disappeared].>>

Mickey Mortimer wrote:

<In Ornithodesmus, the first two sacrals have
pleurocoels, but the posterior ones are to poorly
preserved to tell. As far as I know, oviraptorids are
also supposed to have full sacral pleurocoely, as does
the Brazilian "oviraptorosaur".>

  About that specimen, SMNS 58023, the condition is
not fully determinable, because of lack of
preservation of the sacrum. Frey and Martill (1995)
show that the last sacral had a pleurocoel, and thus
"all sacrals" may have been pleurocoelous, not what I
would determine without seeing the other sacrals,
which may or may not have been pleurocoelous. These
vertebrae are apparently the most posterior of the
series, and the last sacral has the largest
pleurocoel, the others have tiny little slits, which
suggests a differential morphology, though not
divergent of the oviraptorosaur condition. Complete
sacral pleurocoely is present in ornithomimosaurs
(*Gallimimus*, Osmolska et al., 1972) so the
identification of oviraptorosaur? should be changed to
maniraptoriform?

  Found the other references, or at least the ones
commented on earlier.

  Interesting things, too. The cervicodorsals of
*Avimimus*, according to Kurzanov (1981), are
playcoelous and do not perserve either the neural
arches, or any indication of pleurocoels (pg: 42-43)
[please note: I am using the Russian version, not a
translation, so I may have something in error;
regardless of how I may come across, I'm not perfect].
Norman (1990) reillustrates figures from Kurzanov
(1987), and these indicate more midseries cervicals
with pleurocoels, and dorsals with pleurocoels.

  Additionally, *Beipiaosaurus* (Xu, Tang, and Wang,
1999) lacks cervical pleurocoels, but possesses a
lateral central depression (pg.: 351). This would
suggest that the Liaoning form secondarily closed the
cervical pleurocoels; that therizinosaurs and
oviraptorosaurs acheived their pleurocoely seperately;
or that the Liaoning form was not on the road to
pleurocoely, so to speak, that it lies outside the
Alxa+Ovi clade, whatever that would be, and is more
basal than all. I find this totally unlikely.

  Lastly, checked Russell and Dong, 1993, and indeed,
to my error, there is a single lateral pleurocoel on
the cervicals, or at least one of them (pg.: 2113) in
*Alxasaurus*.

  It is my impression that pleurocoely was never a
good definition for diagnosis in this group, or
outgroups, because of the plastic means by which
recent theropods have been shown to exhibit vertebral
pleurocoely (sauropods but not prosauropods,
*Achillobator*, dorsals and sacrals in ornithomimes,
partially sacral and dorsal pleurocoely in troodonts?,
etc...) to an extensive degree, and so-called
oviraptorosaur/therizinosaur theropods like *Avimimus*
or *Caudipteryx*. The Patagonian cervical (Frankfurt
and Chiappe, 1999) has a single pleurocoel;
*Microvenator* has an axial pleurocoel, but not more
posterior cervicals (Makovicky and Sues, 1998 - I said
1997 previously) but has "depressions"; NMV P186302 (a
dorsal) from Australia (Currie, Rich, and
Vickers-Rich, 1996) has extensive internal
pneumatization and a pleurocoel; the Brazilian sacrum
(Frey and Martill, 1995) has larger more posterior
central pleurocoels than anterior, and the
anteriormost sacrals may not even have any
pleurocoely.

  Such a complex at the base of the tree with
fragmentary fossils and incomplete data suggests that
little resolution can be made without much more of the
vertebral series in each form.

=====
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

Qilong---is temporarily out of service.
Check back soon.

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