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Powered Flight Definition (part of RE: Cost in Aquatic Birds (long))
<<yeah, except that it requires a precise coordination that must be
produced through effort within the medium. The data evidences that the
power stroke was produced _after_ the animal was airborn.>>
and Tim Williams (TiJaWi@agron.iastate.edu) wrote:
<I don't see why this is the case - not at all. Are you suggesting that
the power stroke was added at a *later* stage to an animal already capable
of parachuting or gliding?>
Let me explain later why I think this may be likely. However, fossils
indicate that *Archaeopteryx*, though a flapper, could not power-flap, and
the same goes for *Confuciusornis* and *Chengchengornis*.
<By "this capability" I assume you mean powered flight - the "flap" that
turns a passive glide into active flight. Again, I don't see why
_Archaeopteryx_ or _Confuciusornis_ would lack this trait. They look to
me to be capable of sustained, flapping flight.>
I think I need to clarify what I mean by powered flight, however. The
power flap, or power stroke, in the bird wing, also present in the bats,
is a result of the presence of a triosseal canal. I previous indicated
this. The reason being the condition is neccessary for the rotation of the
humerus about it's long axis as it is being elevated above the horizontal.
The nature of the scapulocoracoid glenoid and the acromion and joint
between the scapula and coracoid show that until Enantiornithes, birds did
not have a triosseal canal, nor did they have a particularly
dorsally-apparent glenoid, that could be used to suggest the presence of a
elevation-rotation phase of the wing-path, and thus a power stroke.
<Don't look now, but I think you've just reinvented Feduccia's
"sifaka-like proavian" hypothesis for the origin of avian flight!
However, to bring the above model into line with Feduccia's model, just
substitute "theropod" for "I'm not sure what gave rise to birds, but it
wasn't a theropod but probably some kind of thecodont (whatever that might
I have wondered about a functional attitude for the brachial structures
on *Sinornithosaurus* for a while now, trying to separate the idea of
display and put them into an aerodynamic context. Brian Cooley's model
shows this off rather well, I think. I looked for possible
re-interpretations, without trying to evidence any particular assumptions,
and I saw *Sinornithosaurus* as a trunk-branch clammerer and
short-distance leaper. In this fashion, the arms would seem particularly
suited to assisting, sifaka-like, in leaps across intra-arboreal
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.
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