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Re: Microraptor biplanes?



Scott Hartman (dinoboygraphics@aol.com) wrote:

<Well, I guess I should be pleased that Chatterjee took my CLPV II presentation
to heart; he isn't arguing for splayed hind-limbed mircroraptors.  I have my
doubts about this particular configuration, but at least it's a novel approach
that doesn't violate the hind limb anatomy.>

  I argued back in January and February of 2003 on the list that the leg would
need to be tucked in the manner illustrated in order to take advantage of the
feather structure of the hindlimb. That is, the feathers with a chambered
surface indicated by the shorter vane on one side of the rachis than the other
shows that the leg feathers, with the shorter vane toward the foot in
orientation, were horizontal and (mostly) lateral in orientation or with mild
back-swept form. I illustrated this here:

  http://www.deviantart.com/view/16284140/

  This illustration is not perfect, I admit. But it illustrates the ideas I
describe here better than the "diagram" does:

  http://www.deviantart.com/view/24047375/

  The dotted line refers to the position I describe as being the more likely
position that provides sufficient explanation to take advantage of the camber,
shortened leading edge, and backswept angles of the feathers (as preserved).
The bold lines of the hidnwings illustrate the other position when the leg is
tucked that takes advantage of lift and drag-generating features to aid in the
animal's control in the air, as Jim Cunningham has argued was possible.

  In the painting, the hindwings are not shown tapering on the leading edge,
but straight-edged with the first feather (closest to the phalanges) as the
longest. This position (both mine and illustrated) does not take advantage of
the fact that the feathers, while much shorter, continue around the ankle, an
arrangement suited to an extended ankle, not a tucked one. Thus the leg may not
have functioned as a perfect plane, but better as a drag-inducing foil with
"tufting" around the ankle and along the tibia. Paul argues these feathers
continue along the thigh (unpreserved) and met the tail, as theorized to exist
in the brachial wings as well, but if his theory is true, an extended leg (as
he illustrates in Paul, 2003: Screaming biplane dromaeosaurs of the air.
_Prehistoric Times_ 30:48-50) may serve the same function as I show in my bold
lines, only throughout the leg. The primary reason he illustrates the leg in
this position, for the purpose of "flapping", can be ignored if the extended
leg (given the muscles as in birds, would this be physically possible?)
provided aerodynamic reasons to be extended, without flapping. But the form of
the feathers on the metatarsus also argue that the leg could not function
extended to the rear, nor could the leg "flap" given the morphology of the hip,
nor could it extend sideways, for the same reasons. This leaves tucked and
ventral extension as the most likely alternative positions.

  Cheers,

Jaime A. Headden

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


        
                
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