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Re: [Re: Reptilia]



Philidor11 wrote:

<The definition based on common ancestry therefore implicitly
identifies a set of animals which meet the selected set of problems
a,b,c... by ...x,y,z. The characteristics are (at least the physical
aspect of) x, y, and z, and the definition assumes that we know what
a,b,c are. (In my case, this may be excessive confidence.) The
presence of a characteristic implies its purpose and the purpose is
the core of the definition. The purposes selected apparently control
classification.
 
  I suspect that I'm missing something, logical, but missing something.>

  There is something to be said of function-related characters. I'm
sure Tom Holtz'll say something on this, but analyzing the
oviraptorosauria as I am, I am faced with detirmining which characters
may be stronger than another, and which ones have no bearing on the
matter. As it is, there is one function-related characters that help
define Oviraptorosauria which at the moment are unambiguous: loss of
maxillary/premaxillary/dentary teeth. Toothlessness is an odd
character to work with because you get to wondering "why be
toothless?", and "what would be the benefit of being toothless?" It's
possible diet is a factor, but there are toothed shell-crushers and
toothed and toothless piscivores and toothless carnivores, so we are
left wondering, "what is most likely?" Or at least _I_ am left here
scratching my head.

  *Caenagnathasia* is an example. It possesses distinct dentary dental
alveoli, unlike all later oviraptorosaurs. As I haven't gotten the new
*Microvenator* paper, I have no clue on the new material being
abscribed to it.

  All other caenagnathid jaws show vertical ridges that correspond to
the interdental bone: only the lingual ridge of the jaw is missing,
having been lost sometime earlier (there's an unknown oviraptorosaur
out there, therefore, that fits into this hole). This suggests a
caenagnathid relationship, as there seems to be a series evident. All
oviraptorid jaws lack these ridges. The morphology of the jaw is
similar to caenagnathids, more so than to oviraptorids, and this
suggests a caenagnathid relationship.

  If the character can be assumed to be basal to the entire group,
toothlessness becomes a defining factor of oviraptorosauria, and
*Caenagnathasia* is placed outside of Caenagnathidae based on it's
shear morphological distinctiveness. I illustrate this point on my
site, to some degree; recent work has allowed me to elaborate further.

  This demonstrates the systematic usefulness, and headaches thereof,
of function-related characters, this one possibly stronger than some
(ankylosaur armor morphology?).

  So, the fun continues. I hope this does soemthing to alleviate your
quadary, Philidor.

==
Jaime A. Headden

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

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