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Re: [Re: Reptilia]



Philidor wrote:

<Your comments do help, but I do have a question. You appear to assume
that there is a group of animals called Oviraptorosauria and your job
is to choose among the common characteristics to find the
functionally-related ones.>

  My "job" is to figure out the relationships of oviraptorosaurians
amongst each other, and the group to other theropods, if to see if any
taxon is closer to any other non-oviraptorosaurian taxa, or not, and
form a diagnosis based on such. I love it, too, absolutely.
 
<Taking a step back, how do you know that these animals are
Oviraptorosauria?>

  There are numerous characters shared by *Chirostenotes* and
*Oviraptor*, with varying degrees of functionality:

  1.  articular and surangular fused together,
      possibly with coronoid (ASC complex of Currie,
      Godfrey, Nessov, 1993)
  2.  coronoid dinstinct, deflected medially
  3.  splenial confined to anterior half of mandible
  4.  manual unguals with dorsoventral "lip"
  5.  mandible laterally bowed
  6.  pubis concave anteriorly
  7.  anterior process of pubis longer than posterior
      process
  8.  articular cotyles distinctively inflated
  9.  dentary posteriorly bifurcate: the dentary has
      two dinstinct processes, dorsal and ventral,
      formed by anterior placement of the external
      mandibular fenestra
  10. metatarsal III proximally appressed between II
      and IV

  Features 1 and 3, 5, and 8 are all unique to the group; 4 and 6 are
also shared by therizinosauroids (though in 6, the pelvis is
opisthopubic); 9 is also found in birds; 10 is modified in
caenagnathids. As established by Currie, Russell, Osmolska, Barsbold,
Holtz, and Sues, Oviraptoridae and Caenagnathidae are each others
closest relatives, based on several of these characters.

<You seem to imply that Oviraptorosauria is diagnosed by at least some
non-functional characteristics. Do you have a known, specific basal
animal and obvious direct descent? Or geographic proximity of animals
with 'important' similarities?>

  John Jackson, not so long ago, said that there are no characters
that are not function related. Every aspect of our biology evolved to
do _something_. But the obvious ones, like toothlessness, are really
strongly evident. Others, the concavity of the pubis, lateral bowing
of the mandibles, and form of the dentary with relative position of
the external mandibular fenestra, are less strongly functional, though
two might be argued to give muscular and functional effect to feeding
(eggs?).

<Some organizing principle is implied by the existence of
Oviraptorosauria, and it is not physical characteristics, which
diagnose but do not define.>

  The definition is "all taxa closer to *Oviraptor* than Neornithes".
Since by various analyses (Gauthier, Gauthier and Rowe, Holtz) have
produced data which show dromaeosaurids (and Archie) are
Oviraptorosauria's closest outgroup, this can be shown that any animal
with a closer morphological similarity to ovis than dromies (after
first dismissing the rest of Theropoda as possibilities) must be an
oviraptorosaurian. This presently includes *Chirostenotes*
(=Caenagnathus) and *Oviraptor*, thus also includes *Elmisaurus*,
*Ingenia*, *Conchoraptor*, "*Rinchenia*", and *Caenagnathasia*. It
also includes, apparently, *Microvenator*, which shares numerous
synapomorphies with caenagnathids and oviraptorosaurians in general.

  Those features and the definition above pretty much ensures that
there will always be an Oviraptorosauria, and as long as
*Chirostenotes* is more similar to *Oviraptor* than *Archaeopteryx*
(or Neornithes), so shall all caenagnathids be oviraptorosaurians.

<Your post implies it is not function, which is a large part of
adaptation.>

  I cannot detirmine, yet, a function for the edentulous condition. I
may not; I do not assume I can. However, such a feature has an
enormous amount of strength, even given it's variability in two groups
of theropods (Oviraptorosauria and Ornithomimosauria, who by fossil
sequence arrived at the condition independantly) and one possible
theropodan group (therizinosauroids). Possibly different reasons for
each group.

<Hrmph.  I used to spend hours lost in the stacks at Sterling Library
on questions like this, wishing there was course credit.  Anyway,
thanks.>

  I can't wait to spend hours studying in a library. Really! :)

==
Jaime A. Headden

Qilong, the website, at:
http://members.tripod.com/~Qilong/qilong.html
---
All comments and criticisms are welcome!

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