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Re: Jeholornis as Oviraptorosaur?



Rutger Jansma (not "Fam" -- fam.jansma@worldonline.nl) wrote:

[snipped]

  *Jeholornis* as an oviraptorosaur? Curious. Plausibile, but my
examination suggests something different. Point by point:

<The lower jaw was the first thing that made me think of this, this was so
similair to the condition found in Caudipteryx, Incisivosaurus,
Caenagnathids and Oviraptorids to a smaller degree,...>

  Superficial similarity of the lower jaw. I will nip any comparisons of
the lower jaw in the bud now. There is no external mandibular fenestra;
the left mandible has a large area of unpreserved bone, but the right
mandible is complete with a smooth caudal margin that contacts both
surangular and the apparently missing left angular; there is a foramen at
this juncture.

  The recurved dentary is interesting and certainly comparable.

  The symphysis is unfused (as in *Caudipteryx* and *Microvenator*) and it
lacks the caudal symphyseal shelf as seen in oviraptorids,
*Chirostenotes*, *Incisivosaurus*, and *Caenagnathasia*.

  The splenial is tall and triangular, unlike any oviraptorosaur, and
there is no rostral extension of the Meckelian canal towards the
symphysis, which *Incisivosaurus* has as well, but no other
oviraptorosaur.

<The second character observed in the skull is the reduced maxilla>

  The maxilla is incomplete in *Jeholornis*, and a "reduced maxilla" is
fairly subjective. Most birds have a triradiate strut-like maxilla whereas
the oviraptorosaur maxilla is plate like with a caudal ramus and a medial
plate.

<The jugal shows a distinct curvature upwards, which approaches the
ndition seen in the Ovi's, but not totally, this is to be expected within
a basal genus of a clade.>

  Actually, all oviraptorosaur jugals are strait ventrally; you may be
referring to Paul's restoration of ZPAL MgD-I/95, referred to *Oviraptor*
sp. by Osmólska in 1979, and by Paul to *Ingenia*, which unfortunately
lacks a jugal entirely. All other oviraptorosaur jugals are straight
ventrally or, as in *Caudipteryx* and *Incisivosaurus*, similar to
*Velociraptor*.

<Fifth, the near-mesopubic condition, which is a clear reversal from the
condition seen in Archaeopteryx, which has a strong opisthopubic
condition. A mesopubic is also a condition seen in Ovi's, though the
distal curvature seen in at least Ingenia makes it appear to look like a
propubic-conditon.>

  The pelvis in *Jeholornis* is distinct, but its the pubic morphology and
not the angle of the pubis that is important, and in this the pubis does
not resemble any oviraptorosaur, not even *Caudipteryx*, especially in its
sigmoidal curvature and superficially *Rahonavis* appaearance (but not
vertical orientation).

<Last, but not least, the similarities in the the caudal count. The
reduced caudal count is something that appears to be almost diagnostic for
the Enigmosaurs and this is best seen in genera like Caudipteryx and
Nomingia were complete caudal counts can be observed.>

  Caudal counts vary from 26 to 36 in oviraptorids, around the
mid-thirties in segnosaurs, and 22 in *Caudipteryx*. It is not a
consistent count that can be described phylogenentically, except less than
40 caudals. If there is any reality to Segnosaur + Oviraptorosaur
monophyly.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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