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RE: Caudipteryx (was Re: Just following the trend of questioning. ..)



Time Williams (TiJaWi@agron.iastate.edu) wrote:

  [on reduced third digits]

<What about alvarezsaurids and carnotaurines?>

  For the latter, not enough of the manus is known to know exactly how
many digits are present. I can offer that some known condition of the
fourth metacarpal is highly derived, but this is non-provable without an
articulated manus. As for alvarezsaurs, there's only one manus known (for
*Shuvuuia*) which preserves manual digit three, and it is complete with
claw. *Mononykus* preserves metacarpal III as fused to II and the carpus,
but there are no digits preserved despite the retention of a distal ball
joint [which would, as is the case in *Compsognathus*, indicate a third
digit of at least one phalanx]. Nothing more complete is known, but
absence of evidence is not evidence of absence.

I wrote (I may have sent this to Tim privately by accident, if not thanks
for sending it along, Tim):
 
<<Problematically, caenagnathids (improp. elmisaurids) have broad
interpahalngeal joints that would make this difficult, if not impossible.
This indicates a robust articulation, and this is even more etxreme in
*Elmisaurus rarus* than it is in any other taxon; in fact, the ration
between width of the distal and proximal ends and the shaft width is
diagnostic to the taxon so far.>>

<I found this extremely interesting.  However, I don't see how this
precludes syndactyly in elmisaurids.>

  Because the robustness of the third and second digits prevents their
being parallel. I can further state that the articulations are not
aligned, and the third metacarpal is shorter than the second, providing a
condition not known in syndactylous animals (some birds, diprotodont
marsupials) where phalangeal count is similar, joints are aligned, and
metatarsal-phalangeal joints are aligned. This is just not the case in any
caenagnathid manus I have seen. Furthermore, the metacarpals appear to
diverge to far for the base of the digits to conform, though not as far as
Ostrom's *Deinonychus* manus, it was not as close to parallel as in
oviraptorids. This may be the case in some animals with
similarly-proportioned second and third digits, as occurs in some
dromaeosaurids and ornithomimosaurs, but otherwise there is no concurrence
in oviraptorosaurs of any stripe for syndactyly [at least from what I have
seen].

  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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