On Conchoraptor?

["Jaime A. Headden" <qilongia@yahoo.com>]

>From _Naturwissenscheften_, available online pre-press, is a new paper on an
oldie but goldie oviraptorid, *Conchoraptor*. That's what the title says,
anyway.

http://www.springerlink.com/content/t37036v812v7m021/?p=2d9d9538d9f44f278c82ca1012d6dd82&pi=0

[the link may be cut off and wrapped, so I recommend cutting and pasting if
this continues]

  Kundrát, M. In Press. Avian-like attributes of a virtual brain model of the
   oviraptorid theropod *Conchoraptor gracilis*. _Naturwissenschaften_ Online
   First. DOI: 10.1007/s00114-007-0219-1

Abstract:
  "An almost complete adult endoneurocranium of *Conchoraptor gracilis*
Barsbold
   1986 (Oviraptoridae; ZPAL MgD-I/95), discovered at the Hermiin Tsav locality
   (the Upper Cretaceous) in Mongolia, is analyzed. A virtual model of the
   endoneurocranial cavity was derived from CT scans and represents the most
   complete maniraptoran endocast to date. It displays reduced olfactory bulbs,
   large cerebral hemispheres in contact with the expanded cerebellum, an
   epiphysial projection, optic lobes displaced latero-ventrally, presumptive
   cerebellar folia, enlarged cerebellar auricles, and a deep medulla oblongata
   with a prominent ventral flexure. Contrary to *Archaeopteryx*, the shortened
   olfactory tract and cerebellum overtopping cerebral hemispheres of
   *Conchoraptor* resemble conditions in modern birds. Calculating brain mass
   relative to body mass indicates that *Conchoraptor* falls within the range
of
   extant birds, whereas *Archaeopteryx* occupies a marginal position. Most of
   the endoneurocranial attributes, however, have a less birdlike appearance in
   *Conchoraptor* than do corresponding structures in *Archaeopteryx* and
modern
   birds in which 1) postero-laterally expanded hemispheral domains broadly
   overlap the optic lobes, 2) the epiphysis projects to the posterior
cerebrum,
   3) lateral extension of the optic lobes substantially decreases a brain
   length-to-width ratio, 4) optic lobe and anterior hindbrain are superposed
in
   lateral view, and 5) cerebellar and midbrain compartments are in distinct
   superposition. The endoneurocranial characteristics of *Conchoraptor*, taken
   together, suggest that the animal had a keen sense of vision, balance, and
   coordination. The data presented in this study do not allow an unambiguous
   assessment whether the avian-like endoneurocranial characteristics of the
   flightless *Conchoraptor* evolved convergently to those of avian theropods,
   or indicate a derivation of oviraptorosaurs from volant ancestors."

  The skull being used, of course, is one of the first skulls avaialble from
the Polish expeditions to Mongolia, ZPAL MgD-I/95, a tiny little thing less
than three inches long, and about the same size as the type skull of *C.
gracilis*, GIN 100/21. Kundrát reconstructed the virtual endocast using scans
of the skull and tracing them out, then reassembling them in layers, developing
a 3D look inside the skull.

  The abstract really tells much of the story. In comparing the edocasts
between Concho, Archie, and an ostrich, Kundrát finds that the oviraptorid
brain is much more like that of the ostrich than is Archie's, implying it
derived from volant ancestors. This is, of course, assuming that Archie didn't
develop flight independantly from main-line, modern birds. Kundrát also argues
that the brain-size to body-weight ratio is much higher in Concho than it is in
even *Troodon* skulls analyszed by Currie and Zhao in 1994 (cited 1993), but I
find it difficult to estimate body size since the specimen analyzed is an
isolated skull; specimens of *Conchoraptor*, including the type and original
referred specimen GIN 100/22A, including postcranial material, and these reveal
a relatively small-headed animal. However, Kundrát doesn't cite his comparative
math, nor does he refer to which specimens are being measured. Moreover, he
uses rhea as a comparative body size to estimate body mass, and this seems
particularly odd, as Concho is not a rhea, or even remotely similar (for
example, the robust arms and tail, relative head size, neck shorter, and torso
less compact with large pelvic anatomy, broad rather than conserved pes, etc.).

  The big story of the paper, though, is the tale of secondary flightlessness,
where the brain is clearly derived from an avian-form, to which even
*Archaeopteryx* is basal compared to birds. Here, we have a birdy brain in a
not-so-birdy body, while in Archie we have a bird-sih brain in a very birdy
body, telling us that Archie is conserved regarding body plan, and Concho and
friends are much more derived and ended up loosing the power of flight. This
argues without an analysis or referrenced phylogeny and any explicit means to
determine which phylogeny is more correct, though to be honest most publish
coelurosaurian phylogenies place Archie closer to birds than are oviraptorids.
The paper was also looked over by the esteemed Mrs. Osmólska and Maryañska
[forgive the tilde, ASCII keyboards have a difficulty -- as in, inability --
making the acute-n sign], and I have no reason to expect that the intended
phylogeny is the one presented by the latter and supported by the former in the
past 5 years, placing oviraptorids closer to birds than Archie and
dromaeosaurids. This is to say, not that I disagree with them, but to put the
phylogenetic context into place. Kundrá cites both works by Elzanowski (1999)
and Maryanska et al. (2002) in favor of this placement of oviraptorosaurs, and
one study, Xu et al. (2002), in favor of the alternative. Since there have been
many, many other studies to support Xu et al. (albeit much of them by Xu et
al.), it seems odd to incipiently tilt the analytical favor towards the more
recent theory, which at least here (Mickey's tireless doggedness at perusing
matrices) have been shown to be at least somewhat flawed in their results.

  Nonetheless, what we have now is a complement to the ongoing attempts to
brainscan all theropods, on the heels of Franzosa's thesis, which also
CT-scanned the type skull of *Citipati osmolskae*, among other maniraptorans.

  Yet, a question surfaces when I read this paper. This is the first time I
have seen this specimen attributed to *Conchoraptor*. Indeed, it was originally
placed in *Oviraptor* as *).* sp. (as mentioned in the paper), but has later
been usually granted as the poster child of *Ingenia*, given it was the first
crestless oviraptorid skull found in Mongolia. Kundrát's justification is
brief:

  "ZPAL MgD-I/95 was described as *Oviraptor* sp. by Osmólska (1976) but is now
   diagnosed as *Conchoraptor* Barsbold 1986."

  I suspect this has to do with the registry in the ZPAL and the views of
Osmólska and/or Maryañska on the matter. I would beg to differ, but I have seen
less skulls and in less detail than they, so I will not quibble too much except
to compare the skulls themselves, to the best of my ability.

  Both GIN 100/21 and ZPAL MgD-I/95 are very nearly the exact same size, and
have the same essential orbital diameter as one another, given the shape and
placement of the orbital rim of the frontal, and the length of the
maxilla/premaxilla relative to one another. This aids direct comparison hugely.
GIN 100/21 is, unlike the Polish specimen, mediolaterally crushed by about 30%,
with the right side displaced caudally and ventrally. Despite this, the left
side shows the dorsal surface of the nasal and frontal is inflated and the
surface bears numerous openings and pits, as in *Khaan*. In ZPAL MgD-I/95, the
skull is less dorsally pneumatically "excavated" (if the features aren't eroded
in the Mongolian specimen anyway), though the specimen is much less crushed. It
is, however, missing the left lateral surface of the braincase, and whole
sections of the parietal and the entirety of the supraoccipital are missing.
Kundrát illustrates the skull in left lateral view, and shows the quadrate is
missing, though based on Osmólska (1986) it has been removed for examination
(previous work by Osmólska, 2002, included a study of the internal
architechture of oviraptorid quadrates). The largest feature compared between
the two is likely the enormous nasal aperture in GIN 100/21, rather small in
ZPAL MgD-I/95, which was used by Clark et al. (2000), to diagnose *Khaan* in
comparison. The external nares are oval and huge, nearly the diameter of the
antorbital fenestra, while in ZPAL MgD-I/95 they are only 60% the diameter, if
that. Probably less distinct but nonetheless peculiar, GIN 100/21 possesses a
smaller ectopterygoid than does ZPAL MgD-I/95, despite being the same size of
head, which would probably distinguish them habitually as well.

  But this argument that ZPAL MgD-I/95 does not belong to *Conchoraptor* is
entirely outside the issue of the brain anatomy, one I am not competant in
assessing at this time, as there is only one other CT scan of an oviraptorid
braincase, and it is not even pulished (see Franzosa's thesis). However, just
looking at the endocast, we can say somethings with confidence: It had
enourmous optic lobes. These lobes, adjacent to the cerebral hemispheres (which
themselves preserve a distinct fissure with large epiphysis), are only
consistent with the enourmous orbits of oviraptorids, and argue that the eyes
were not only large, but extremely acute. This despite the eyes having less
stereoscopic overlap than do, say even dromaeosaurids or troodontids. So, we
may be left with a question:

  What use huge, powerful eyes that had limited overlap? Were they crepuscular
animals, or nocturnal? Suited to doing their foraging (or hunting) at night,
when other predators were tucked away cozy in their Denver the Lost Dinosaur
comforters?

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


 
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