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Re: Resolving the Digit Loss Debate?



Okay, replying to David and George here, at the same time:

George Olshevsky (dinogeore@aol.com) wrote:

<Early dinobirds had five loci for airfoils on their body: the
tail and the four limbs. The first of these to develop an
airfoil function must have been the tail, mainly because it's
simply the part that needs the least modification to become one:
just grow a fringe of feathers and voila.

  With regard to the limbs, they don't have to be able to extend
sideways from the body (let alone up over the back as in avialan
birds) in order to have an aerodynamic function; given a
suitable fringe of feathers, they can be aerodynamic at pretty
much any angle.

  We're not looking for perfect flight here, just something to
mollify the effects of a fall (as in fluttering) or to help
control the midair course of a leap.>

  Just to clarify something: in ceratosaurs and more basal
dinosauromorphs, at least, the scapula possesses a supraglenoid
ridge that prevents the humerus from adducting more than about
10 degrees from the vertical. The humerus pulled backward
(flexed to the shoulder) is still not an ideal airfoil with the
contraction of the forearm that is requisite in humeral flexion.
This makes even the vertical airfoil irrelevent to retarding a
fall. It may help in the lagosuch and coelophyse running along
its merry way, but I cannot see any other way this would work. A
tail "spray" would be interesting, however :)

and David Marjanovic (david.marjanovic@gmx.at) wrote:
 
<Sure, but why a tendency to make the playing-the-piano position
for the hands impossible? And why the loss of fingers??? The
hands of theropods could arrest them only when they crash
_laterally_ into a trunk, not ventrally, AFAIK (but the feet
could accomplish this).>

  Only quadrupeds have their manus in the palm-backwards
position, or partially supinated. All bipedal dinosauromorphs
seem to have oriented the palm medially and caudally, including
hypsilophodontids. This is based on the orientation of the
radius to the wrist and on the humerus itself.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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