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RE: Archaeopteryx running & CNN report on the feathered dino



 

Jim Cunningham wrote:

> More seriously, once you develop an effective supracoracoideus, you no
> longer need the cursorial ability (this has to do with landing, not
> with trees down or ground up theories). And once you develop the
alula, 
> you no longer need the hand to assist with vortex control during 
> flight. 

Again, this is assuming an overriding selection for improved flight
ability in early avian (and "pre-avian") evolution - up to and including
_Archaeopteryx_.  What if the first birds retained good-running ability
so they could chase down prey on the ground?  What if they had grasping
hands so they could grab prey?  

I'm not disagreeing with your aerodynamic interpretations; the use of
the appendages in ground-level predation is not mutually exclusive with
an aerodynamic function.  However, there is the possibility that the
reason why _Archaeopteryx_ has a grasping manus, cursorial hindlimbs and
long tail is for the same reasons that its ancestors did.  


>Why do aerodynamic benefits have to be limited to higher, longer, more
>precise leaps? 

Oh, they don't have to be limited to this.  I was continuing on from the
premise that *if* incipient aerial behavior took the form of
prey-catching leaps, then there might be good reasons for retaining the
ancestral maniraptoran body plan - at the expense of better aerodynamic
abilities.  I'm not arguing this is the *only* possible behavior that
could have given rise to flight.

>What is there about Archaeopteryx anatomy that indicates that it was a
>particularly inefficient or ineffective flyer? 

Puny sternum.  Lack of a supracoracoideus pulley system (as you note).
I don't dispute that the frond-like tail could have acted as a sort of
"third wing" for the legs.  But you must admit - the long tail is pretty
"draggy".


David Marjanovic wrote:

> >The specimens of _Archaeopteryx_ do not show hindlimb feathers
(contra
> >some early interpretations).
>
> What else are the contour feathers on the shins of the Berlin
specimen?

I didn't know about tarsal feathers in _Archaeopteryx_.  Are you
certain?

>Don't know about tertials, but many contour feathers on the body of the
>Berlin specimen were _prepared away_ to reveal the bones. Read more in
><duck and cover> Feduccia 1996.

I don't think this issue has been settled beyond reasonable doubt.
However, I am aware that some early sketches of one of the
_Archaeopteryx_ specimens do show contour feathers (can't remember which
one - was it the Berlin specimen).  But this doesn't hold for *all* the
_Archaeopteryx_ specimens.  If one Archie specimen did preserve contour
feathers, then it's exceptional in this respect.

>I think because they don't retract their legs when they fly; to
minimise
>drag, they have streamlined shins, in analogy to aeroplanes with fixed
>wheels.

Interesting.  

Other birds have leg feathers too, such as some owls and sandgrouse.
Maybe they're used as leg warmers?


Tim


------------------------------------------------------------ 

Timothy J. Williams 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 3163