Re: "Flight theory has legs"

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

John Conway (john_conway@mac.com) wrote:
 
<Chris did not look at hand claws (and made that clear) - the predatory 
function of the hand claws in many species would have clouded his results
at this early stage. After talking to him at length about his thesis, I'd
have to say that his position on the origin of flight is somewhat more
complex than the article would suggest. He is also looking at the
possibility of a functional split that would allow the hand and foot claws
to specialise for different tasks.>

  If his results indicated a variability in habitat to foot function, re:
terrestrial vs. arboreal on the basis of curvature of pedal claws, he made
an _a priori_ assumption that manual claws did not have a substrate
locomotoral capability. I would think this is an essential issue that
should have been resolved prior to comparing extant birds to fossil birds
and thereby extrapolating behavior and habitat to the past. This is a
problem Horner has in prevailing issues on forelimb use to corroborate his
scavenger theory for *Tyrannosaurus rex*. However, the presence of manual
claws in an arboreal or terrestrial animal should be considered, in light
of the fact that extant birds lack locomotorially functional maual claws
with the exception of juvenile hoatzin, as a functional possibility. If
the pedal claws are decurved, but the manual claws strongly curved, does
this not raise particular issues? No bird alive has this suite, and
inferring that a roadrunner with manual claws could not use those manual
claws is the same as stating that *Confuciusornis* is more likely
terrestrial, contra any conclusions on its manual claws. Previous analyses
indicate that the use of both manual and pedal claws can be exapted to the
same degree, as in colugos, squirrels and other terrestrial sciuromorph
rodents, and bats, but that the size and claw shape in some bats show a
greater use in one set than another for climbing (megachiropteran bats
hang by the foot claws, whereas never contact the substrate with the
manual pollecial claw) resulting in a shape dichotomy between the two.
This seems to be a serious issue in play, and one that should be (or
should have been) resolved prior to the extrapolation of the thrust of the
thesis.

  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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