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RE: Archaeopteryx running & CNN report on the feathered dino



 
Jim Cunningham wrote:

> Why would there be an
> overriding selection for 'improved' flight ability?  

I wasn't necessarily arguing *against* improved flight ability being a
dominant factor in early avian evolution?  After all, _Archaeopteryx_ has
(what appears to be) an entirely workable flight apparatus.  However, the
close correspondence in skeletal anatomy between Archie and small non-avian
maniraptorans can be readily explained by similar lifestyles - IMHO.  

>And wouldn't the
> function of 'improvements' be different for different species?

Certainly.  At a higher level, this is central to the divergence between
"_Archaeopteryx_-grade" birds and the rest (Pygostylia).


>Of course not.  My thumbs are singularly well adapted for holding
>ball-point pens.  

Ah, that's cheating.  Ball-point pens are *designed* to be held by the human
hand.  :-)

> > .....possibility..........grasping manus, cursorial hindlimbs and
> > long tail is for the same reasons that its ancestors did.
>
>Certainly.  My point is that they don't necessarily interfere with
>flight, and may provide flight benefits.

I agree.

>Quetzalcoatlus species (not northropi) has a puny sternum and is one of
>the largest creatures ever to fly.  How does the puny sternum make it
>ineffective?

As a flapper, perhaps.  I admit I'm a dingus when it comes to pterosaurs -
but aren't these enormous pterosaurs thought to spend most of their time
soaring?  Aerodynamically, this is extremely challenging (and probably the
most derived of all aerial behaviors); but at the same time soaring is less
demanding on the muscles and skeleton.  (If I'm totally wrong on this, don't
hold back!)

> As you no doubt know, modern birds can fly in cruise gaits with their
>supracoracoideus cut through (meaning that it is even less useful than >in
archie).

Now we're talking 'cruising'.  For a primitively poor flier that couldn't
flap well, this would just be 'gliding', wouldn't it?

> > But you must admit - the long tail is pretty "draggy".
>
> If it could cascade, then it would have also had many of the advantages 
> of high aspect ratio wings.

Yes, good point...

> >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.
>
>Which was my point too.  They're increasing the fineness ratio (and
>more).

But does apply to a running take-off, as well as after the critter is
airborne?

And from an earlier post:

> >As I said, later birds took a very different path - and the world is a 
> >much better place for it.
>
>I'd be more prone to phrase it as ' - and the world is a much different 
>place for it".  The same holds for the loss of my favorite beasties, the 
>azhdarchidae.  I wish they were still around. 

Gawds, so do I!  But you may need to wash your car more often though.  :-)

Actually, what I meant by my remark that "the world is a much better place
for it" - 'it' being the evolution of the modern avian flight apparatus - is
that it's allowed birds to exploit an enormous number of ecological niches.
This is opposed to the limited options available to the
"_Archaeopteryx_-grade" avians.  The latter did (apparently) persist until
the end of the Cretaceous (_Rahonavis_); but they were outnumbered (and
outcompeted) by the upstart pygostylians.



Tim


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

Timothy J. Williams 

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

Phone: 515 294 9233 
Fax:   515 294 3163