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Re: Opposable Fingers
I had a funny conversation with Bakker on this....
Anyway, coelurosaurs, including *Coelurus* (the
manus refered to *Ornitholestes*, this is inferred
from context), dromaeosaurs, oviraptorosaurs,
dinobirds, tyrannosaurids, and possibly also
compsognathids and *Nqwebasaurus,* have a primary
digit that diverges from the second, with the distal
end of the first metacarpal twisted ventromedially, so
the digit may be parallel in neutral position, but
extension and flexion are on an acute angle to the
sagittal plane of the manus, and the digit orients
medially for the large part.
This angle increases in maniraptorans so much that
the neutral articulation is strongly medial. Whereas
tyrannosauroids have a similar form of the manus that
spread when in extension, but would have converged
when in flexion; ornithomimosaurs have the opposite
articulation, a first digit that is turned inward in
some forms at all positions, somewhat neutrally in
most positions in a few taxa (possibly
*Dromeciomimus,* definately ambiguous *Harpymimus* and
the primitive *Pelecanimimus* -- and I still don't buy
the spinosaur hypothesis).
The third metacarpal appears to be firmly appressed
in most coelurosaur taxa except maniraptorans.
Oviraptorosaurs, troodontids, dromaeosaurs, dinobirds,
"coelurids," and therizinosaurs (convergent with
allosaurs) have the distal end of the third mc
separated from the second mc, and may have exhibited
some rotary capability in the bone. Articulation in
*Archaeopteryx* and *Deinonychus* (see Yalden and the
more recent Maxwell and Ostrom paper) shows the third
digit could rotate under the second, and this is
similar to the manus in troodontids and some
oviraptorosaurs. The ornithomimosaur third mc is quite
firmly appressed to the second, but the bone is
rotated towards the ventral (medial) surface of the
second mc and the distal end is spherical, not
ginglymoid, and the third digit was probably capable
of a good deal of axial rotation. Ornithomimosaur
hands are really strange.
Mikko Hääramo and I discussed the forelimb on the
list a few months back, so anyone can add this to that
to show the articulation of the manus relative to the
forelimb, and Paul (1988) and Makovicky and Norell
(1997, but primarily see Discussion in the 1999 paper)
have discussed the shoulder articulation in great detail.
Jaime "James" A. Headden
Dinosaurs are horrible, terrible creatures! Even the
fluffy ones, the snuggle-up-at-night-with ones. You think
they're fun and sweet, but watch out for that stray tail
spike! Down, gaston, down, boy! No, not on top of Momma!
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