Re: On the Issue of Sprawling Dromaeosaurs (long)

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

Kris Kripchak offers a challenge to think outside the box, at the same
time accusing some of us rejecting the femoral eversion of *Microraptor,*
as being dogmatic. I would like to say that since a dogma must be an
establishment of doctrine, and the more prevalent idea about *Microraptor*
is that the leg was extended outward, I have never been on the side of
this accused dogma. No matter.

  Bony anatomy must precede soft-tissue. If a bone cannot do the action
required, soft-tissue isn't going to make it move more than otherwise.
This is why there is really no way to make soft-tissue influence the
principle of muscular movement unless it is to limit the movement or
determine range of movement. And on that latter, Kris proposes that the
leg may have been held sideways with a medial femur that has been rotated
about its long axis to allow the tibia to project laterally. To do this,
however, the femur must also dislocate. By similar token, a peculiar
airfoil would result from the position of the femur, tibia, and
metatarsus, and the feathers that would presumably come from them. This
would be S-shaped, higher at the hip, declining to the tucked in knee, and
projecting out from the tibia to the metatarsus, and declining once again
at a different angle. What does this perform for the animal?

  If the leg feathers were confined to the lower leg, this would be easier
to use having the leg tucked; Paul argues that because NGMC 91 has femoral
feathers, this is unlikely, but NGMC 91 also lacks metatarsal feathers --
the reverse is true in *Microraptor gui*, though preservation isn't all
that helpful in this regard. We DO know that NGMC 91 and therefore
presumably the *Sinornithosaurus* holotype, lacked distal leg feathers
because of the scalation preserved there and the lack of feathers around
the lower leg in "Dave." This may be ontogenetic. Paul synthesized NGMC 91
and *Microraptor* to give his sinornithosaurs a full leg wing, following
Xu in this. This has been treated as so since the beginning. Here's
another so-called "dogma."

  Paul is correct to push for the apparently rigorous view that if the
full leg were feathered, a wing must be the product, and that this must
have an aerodynamic function when extended. He has yet to prove that any
femur he has called spherical or raised to be so, when the data in fact
argues against it. Similarly, it was Paul who originated the
"leg-flapping" idea, and has illustrated this to some degree and it
appears in his _Prehistoric Times_ article from last year, without a
single illustration to back his claims of these features; as on the list,
only his word is given despite the morphology. However, the presumption of
completeness of the *Microraptor* leg feathers all the way to the hips is
also unfounded, and one cannot provide evidence they MUST have been of the
same form to the hips, which NGMC 91 would suggest they weren't given
these are MUCH narrower, and appear less than cohesive as a barbuled vane
would.

  There are several ways in which the leg will work extended, and several
of these operate on things I have described on the list in the past.

  1) the leg can be extended FORWARDS, where the feathers will point down
or sideways ... this will give the animal a forward canard slightly
underlying the main wing, and presumably interfere in its performance if
the animal flapped its arms -- the leading edge will be pointing forwards,
so this matches the main wing;

  2) the leg can be extended DOWNWARDS, where the feathers will point back
and down ... this would obviously occur during "landing" or leaping
maneuvers, but any aeodynamic performance at this point would be as in
vertical vanes in planes, and not provide lift or thrust -- the point in a
glider would be ... irrelevant, with the leading edge pointing downward;

  3) the leg can extend BACKWARDS, as in some birds today, where the
feathers will point downwards or sideways, but the leading edge will be
inverted into the "trailing" edge.

  There are other ways to hold the legs, but I argued a while back that
only those that place the leading edge forward and form an aerodynamic
foil would be effective and at all useful. This would also have to form a
plane of the entire wing. My tucked-leg theory does not do this as much as
one would be pleased; it is a theory, and I am ever critical of it. While
Paul's flapping-leg theory also purports to solve the aerodynamic
structure, this does so at the expense of the anatomy. Other theories
include a non-aerodynamic function, as in display, and the position would
help to increase the "shade" of the umbrella, brooding theory, but not
explain the shaping of the narrower "leading" edge. Personally, the
"hanging leg" idea, #2 above, is to me the most reasonable current theory,
yet it provides virtually no aerodynamic support and certainly no reflexed
camber would operate to provide any lift or thrust in that position.

  So ... the theory must:

  1) provide a means for the metatarsal and tibial feathers to act in a
single plane;
  2a) allow the position of the leg keep the leading edge pointing
_forwards_ with
  2b) an aerodynamic function;
  3a) match the inability of the femur to evert laterally, and essentially
not twist muscles or tendons as this would require reshaping of the leg
anatomy to make it _repeatable_ and not a strain on the leg (one should
note that bending one's fingers is not a normal function day to day for
the 50+% of us that cannot do this) -- and
  3b) and all the joints must all remain articulated and conform to their
positions.

  So far, NO leg position seems to afford these criteria but the "hanging
leg" one, and it manages to avoid #2b for part of it.

  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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