Re: four winged Archaeopteryx

["Jaime A. Headden" <qilongia@yahoo.com>]

Graydon (oak@uniserve.com) wrote:

> On Sun, Sep 24, 2006 at 04:59:49PM -0700, Jaime A. Headden scripsit:
> >   However, I think tghere is a difference to be shown here between
> >   _aerodynamic efficiency_ and _aerodynamic functionality_. The tail
> >   in *Archaeopteryx*, unlike those of modern birds, cannot get wider
> >   than it already is, and cannot fan out. It is likely that, based as
> >   it is on a nearly rigid spar (the tail core itself), the ability of
> >   the tail to twist about its base axis (as in extant birds) is
> >   extremely limited, and the ability to expand or diminish its aspect
> >   is likely VERY limited, if it existed at all.
> 
<What keeps Archie from folding the tail feathers against the central shaft?>

  I should have been more cautious in what I wrote, so to clarify, let me
rephrase:

  "The tail in *Archaeopteryx*, unlike those of modern birds, have their raches
based on bones, rather than embedded in flesh and muscles, much of which are
analogous to the caudofemoral musculature. *Archaeopteryx* would retain these
muscles only at the base of the tail, which would be very useless in altering
the ENTIRE tail form. This would make the tail effectively incapable of
altering its shape, based on KNOWN means of feather movement. In a bird's wing,
for example, fanning of the feathers occurs passively due to straightening and
unstraightening of the arm (or flexion of the elbow joint), and the musclar
action required to fan the tail is absent in the wing. A similar condition may
exist in *Archaeopteryx*, but the anatomy would be novel and there is no
evidence to suggest it exists. Thus it would seem that fanning of the tail
feathers would most likely have occured AFTER the shortening of the tail in
pygostylians."

  Jim Cunningham asked about cascading effects, which I asusme would be present
in the tail as the airflow over the tail, especially at the end, would mimick
that of extant birds' fanned tails, as well.

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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