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Re: "The X Digit"...a Pteroid bone??



Cait Kiernan (Gothgrrl) wrote:

<No structure (at least no structural analog) is too complex, in
theory, to be reproduced through convergence and/or parallelism.
Certainly the development of the supracoracoideus in avians is no more
complex than their evolution of endothermy, which, assuming there
isn't an avain/mammal connection hidden in the woodpile, would require
that endothermy was developed independantly in each group. Another
example, cranial kinesis. It appears not only in avians (and possibly
nonavian theropods), but, independantly, in squamates, and surely
required a much more complex series of evolutionary steps than would
the independant development of superficially similar flight
musculature in birds and pterosaurs.>

  This is not so confined, but infracranial kinesis in squamates is
very VERY derived, and much different from avian and dinosaurian
cranial kinesis.

  In theropods, studies by a whole slew of people have shown that they
could widen their jaws at a dentary/etc. joint and in the cheeks at a
maxilla/jugal, jugal/quadratojugal, lachrymal/maxilla, maxilla/nasal,
etc. joints, allowing of all things the mouth to expand to the sides
and to a limited degree, to move on a vertical plane.

  Birds, I'll admit, have quite a lot in uncommon, such as a
streptostylic quadrate to allow that bone to move FORWARD (Matt, if
I'm wrong, whack me), as well as nasal/frontal, premaxilla/nasal, and
frontal/parietal hinges, allowing the jaws to move up and down. Check
out a parrot eating a nut sometime, it's amazing to watch their jaws
work.

  Oviraptors can actually do some of this latter stuff, probably to
the envy of all other "non-avian theropods". They have a premaxilla
that can hinge up and down on the lachrymal and nasal, sliding over
both. That and the palate itself possessed more than a few hinges. Oh,
and the dentary was an up/down only sort of bone, showing these
creatures actually had a parrot-like jaw. One more for the road, eh?

==
- Often, it is the man who is brought
  down the path to the end who does
  not see his own steps. -

Jaime A. Headden

Qilong, the website, at:
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