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Gliding Dromaeosaurs Hunt Cats on the Wing [News at 11]



This is really two related posts, so bear with me.

  Henri Rönkkö asked about the pron/sup of dromaeosaur
arms and how locking the arms would not reduce
resistance. Simply being, it is not the elbow so much
as the wrist: locking the elbow puts the wrist into a
vertical position, and the morphology of the
carpal/forearm articulation would preclude flexion and
extension by a great deal. Resistance of a degree that
would reduce the impact of the manus strinking an
object would reduce the arm's capability to "swipe".
This does not seem to be the case, and pardon for the
doctored phraseology, I'm trying to be brief, and if
neccessary, can elaborate on the alternate hypotheses
later. Locking the wrist also limits the degree to
which the forearm can move on the humerus without
bringing the arm out of pronation. First one, then the
other. The ability of birds to pronate/supinate is
incredibly small, and it can be seen that limiting
pron/sup in birds was a derived event from the "swipe"
described for dromaeosaurs.

  Further, Dinogeorge mentioned not being able to
watch a dromie "swipe" anything, and this is certainly
true. However, I was suggesting a possible scenario
that would explain the features of the arm, and not an
attempt to demonstrate anything.

  A few people also mentioned my application of
jaguars to the Origins discussion, and I would like
this to say on my behalf: My use of jaguars was not an
attempt to suppose dinosaurs went through some sort of
cat-phase in their evolution towards birds, but as a
correllate to the scenario offered by someone else to
the dromaeosaur "prey swipe" drive for leaping out at
trees at prey. Jaguars have not developed any special
gliding structures, and this is hardly neccessary:
their relative distance from prey is smaller than
Chatterjee's model (see his 1996 book, associated
papers, etc., Feduccia's take on it (1997, 1999)). So
jaguars are not useful correllates to avian evolution,
as I said in my reply to Kinman; they are useful
correllates, it would seem to me, in the aspect of the
"leap down at food" and in the relative ability of the
arms between dromaeosaurs and felids. Thus, jaguars
may be a model for work on hypothesizing driving
models for the evolution of the dromaeosaur shoulder
joint.

  This is one perspective, and stems from a non-BCF,
non-Paulian perspective in terms of dromaeosaurs
descending from volant forms. And before someone pipes
up on this, no, I do not believe this scenario has
more merit than BCF or Paul's hypothesis ... it is a
model, and merely _a_ model.

=====
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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