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Re: 11th specimen of Archaeopteryx



Michael Habib <MHabib@chatham.edu> wrote:

(I've snipped Mike's explanation of feather symmetry vs asymmetry
solely for space considerations.  Regrettably, because his summary is
the most succinct and comprehensive explanation I've seen to date.)


> In other words, high L:D wing + arboreal adaptations suggests arboreal
> living.  High L:D wing + terrestrial adaptations suggests terrestrial living. 
>  The high L:D wing is not actually that informative, because it
> can apply to either scenario.


Definitely.  Further, although the words "arboreal" and "terrestrial"
are used to describe the lifestyle of avian ancestors, what this
distinction boils down to is the role of gravity in the early
evolution of flight.  A terrestrial pro-avian could have spent no time
at all in trees, but nevertheless used gliding descents as part of its
"terrestrial" behavior.

For example, the modern kagu (a secondarily flightless bird) uses its
wings for gliding while running over uneven terrain.  The Pouncing
Proavis model of Garner et al. (1999) proposed that pro-avians leaped
down onto small terrestrial prey from boulders or logs, and used
incipient wings to guide the descent.

I'm not saying that either of these models are viable hypotheses for
incipient flight behavior.  Nevertheless, they underline the fact that
"terrestrial" does not automatically require that the pro-avian is
always fighting against gravity.  An arboreal ancestry for birds
strongly implies a gravity-assisted origin of flight; but a
terrestrial ancestry for birds is open to scenarios under which the
animal could either be working with or against the force of gravity.


> As a closing thought, I am extremely skeptical of WAIR ability in 
> Archaeopteryx, for reasons I've posted previously.


Yes, me too.  And for reasons I've posted previously (which I suspect
agree with the reasons Mike posted previously) the ability to execute
WAIR might have been beyond any non-ornithothoracean bird.  It is true
that young gallinaceous birds are capable of WAIR, even though their
wings are incipient.  But gallinaceous birds (even the young'ns) are
endowed with an advanced flight apparatus capable of executing a
complete wing stroke; non-avian theropods and basal avians/avialans
were not.





Cheers

Tim