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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
Ah, that's cheating. Ball-point pens are *designed* to be held by the human
> > .....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.
>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
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
> 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
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
But does apply to a running take-off, as well as after the critter is
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.
Timothy J. Williams
Iowa State University
Ames IA 50014
Phone: 515 294 9233
Fax: 515 294 3163