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Re: Archaeopteryx running & CNN report on the feathered dino



Williams, Tim wrote:

> Again, this is assuming an overriding selection for improved flight
> ability in early avian (and "pre-avian") evolution - up to and
including
> _Archaeopteryx_.

Is this an assumption on your part -- or mine?  Why would there be an
overriding selection for 'improved' flight ability?  And wouldn't the
function of 'improvements' be different for different species?

> ...... retained good-running ability so they could chase down prey on
the
> ground?  What if they had grasping hands so they could grab prey?

Sounds reasonable to me.  It doesn't conflict with flight capability.

> the use of the appendages in ground-level predation is not mutually
> exclusive with an aerodynamic function.

Of course not.  My thumbs are singularly well adapted for holding
ball-point
pens.  I doubt that that was their original function, but I've exapted
them
to that use.

>  .....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.

> ......, then there might be good reasons for retaining the ancestral
> maniraptoran body plan - at the expense of better aerodynamic
abilities.
> They aren't necessarily mutually exclusive.
>
> >What is there about Archaeopteryx anatomy that indicates that it was
a
> particularly inefficient or ineffective flyer?
>
> Puny sternum.

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

>  Lack of a supracoracoideus pulley system (as you note).

It doesn't entirely lack the system, it just isn't developed in the same
way
and extent that it is in modern birds.  All you have to do to keep it
from
being a problem is avoid those flight gaits where it is an asset (which
you
can easily do if you have long legs and a long, feathered tail).  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).

> But you must admit - the long tail is pretty "draggy".

Well, actually that depends upon whether it can cascade or not, which
isn't
known at the present time.  And upon the coefficient of lift at which it
is
flown.  There's a good chance that it was invaluable during landing,
since
it had all the aoa advantages of any very low aspect ratio wing.  If it
could cascade, then it would have also had many of the advantages of
high
aspect ratio wings.

> >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.

Which was my point too.  They're increasing the fineness ratio (and
more).
I suggest thinking about the varying effects of alternative wheelfairing

shapes in fixed gear aircraft as an excercise in drag reduction
effectiveness.

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

Sounds good to me.  Most of this stuff has more than one use, and is
likely
the consequence of more than one benefit.

Jim