Re: Feathered Dragons: Studies on the Transition from Dinosaurs to Birds

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

Scott Hartman (DinoBoyGraphics@aol.com) wrote:

<Um, no.  The hindleg feathers are themselves totally novel from any
"bird, croc, lizard, or other tetrapod known today," so no matter what the
attachement or musculature you assume (moveable or not) you are making a
third-level EPB inference.  And even if they were totally arboreal, the
feathers would still get destroyed if they could not fold back when not in
use.  Because the feathers had to be tucked back regardless of
arboreal/terrestrial status, their presence makes not an iota of
difference in the debate, unless one assumes a priori their function.  So
what did they do?  Mor on that later...>

  The feathers themselves exist in birds today. It would not be much of a
stretch of the imagination to assume that birds back to the beginning had
them, and in fact this is supported in the fossil record, all the way to
their toes. The novelty here is the manipulating musculature, which
doesn't exist in any tetrapod I know of, at least. My argument was, in
fact, about the use of a musculature, as in the tail of birds (which
developed from an apparently exapted tail anatomy not analogous to the
long-muscles of the lower leg), to move the feathers automatically.

<The typical theropod everted femur, which becomes more everted as it is
protracted and less so as it is retracted, in no way allows lateral splay.
In dromaeosaurs it simply everts a bit more as it is protracted;  Unless
Microraptor has a pelvis and/or femur totally different from that of say,
Bambiraptor and Deinonychus, there is no way for it to employ the
hind-limb remigies as a "butt-fan," or as to generate lift furing
gliding.>

  I recall making this point all last year prior to the publication of
Paul's article in _Prehistoric Times_ wherein he advocated hindlimb wings
as archetypal as those of the forelimbs.

<Well maybe, depending on how you mean that.  I apologize if I am
misreading you here, but it sounds like you are making Feduccia's classic
mistake of associating aerodynamic function with lift generation in
flight.  With the limbs tucked up during a glide-leap or powered flight
(not taking a position here at the moment) the limbs become
stabilizers/rudders, they could not generate lift.  The aerodynamic shape
would reduce drag from the rudders, and make them more effective.  Unless
someone can demonstrate a unique morphology that would allow the rear
remiges to be used in a manner sub-horizontal relative to the line of the
body, they cannot be butt-fans and/or passive lift generators.>

  Actually, I had in mind the idea that a foil or horizontal wing in
aiding speed and decreasing lift properties, as in Hartman's own
presentation at SVP a few years ago on *Caudipteryx* using wings and tail
as a terrestrial, cursorial adaptation. A vertical wing, on the other
hand, to provide stability, should not be convex on any surface, even when
paired, as seen in the keels of bones, fins in planes, and the fins of car
and dragster spoilers; this would tend to decreasing turning performance.
So I simply chose to discard the idea that when running, these would have
any advantage; however, the idea that they would be _gliding_ adaptations
is very sound, even when one regards the feathers as non-retractile or
foldable during non-aerial locomotion. Current aerodynamic fins in planes
and remote-operated aircraft include slanted canards and tail fins that
perform these actions as precisely as Hartman says they cannot; this
argument was handled largely by Cunningham who offered that they could, in
fact, have a positive effect on lift.

  See:

  http://www.cmnh.org/dinoarch/2003Jan/msg00462.html
  http://www.cmnh.org/dinoarch/2003Feb/msg00009.html

  Note that extensive aerodynamic tests do not accompany these, as stated
largely by Jim via the means by which one should not hold up his words as
"law."

<But if it did so, the lack of specializations to an arboreal lifestyle
suggests it was a secondary spread to the trees allowed by their partial
mastery of the air, not the remnents of a lineage of arboreal scansors
that birds evolved from.>

  What features does *Microraptor* lack that prevent it from being
particular arboreal or scansorial? Aside of course from the unneccessarily
sprawled femur.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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


        
                
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