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RE: Cost in Aquatic Birds (long)
Jaime Headden wrote:
> 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.
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?
> *Archaeopteryx* and *Confuciusornis* lacked this quality, and
> Enantiornithes and Ornithurae attained the capability convergently.
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.
> The first has theropods clamboring in the trees and begin to leap from
> one branch to the other, developing primate-like crania and arms to
> better live in a fully-three-dimensional world; these are predicate to
> leaps to farther and farther branches, until they are jumping from
> trees to spaced trees, then start gliding, and in the effort of
> controlling the flight, develop the flapping capability, and refinement
> produces the 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 be)."
The thing I don't like about this theory (or BCF) is that it implies that
avian ancestors had an extensive heritage in the trees before 'finding their
wings'. Early theropods do show features that could be construed as
suitable for climbing trees (semi-stiff tails, large toes,
long arms, triangular skulls). For eumaniraptorans, the sickle-claw and
retroverted pubis can perhaps be added to the list.
However, when it comes to scansorial or arboreal behavior, said theropods
seem seriously deficient in other respects - e.g. the opposability of the
manus and pes (especially the latter). I'm not saying basal theropods
couldn't climb trees - like small eumaniraptorans, I think they could (and
did) - but they were not *specialized* for this behavior. Thus, I think any
entries up and into trees were opportunistic on the part of predators that
spent most of their time on the ground.
Timothy J. Williams
Iowa State University
Ames IA 50014
Phone: 515 294 9233
Fax: 515 294 3163