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Re: Yet more on dinosaur quad climbers
On Jul 12, 2013, at 5:05 PM, Ruben Safir <email@example.com> wrote:
> You didn't write this?
> "but this does not mean that those effects were the primary function or
> that the limbs were used for a sustained flight function (or, indeed, a
> lift dominated function at all - though it is likely they were)"
> That flight feathers would have evolved for anything other than flight
> would be an extradonary hypothesis that would need extradonary evidence.
Yup, I wrote that, and I stand by it. In fact, I'll go even further: flight
feathers effectively must have originated in a non-flying context, or else the
animals couldn't be aerial to begin with. Now, it could be that the precursors
to the derived flight feather state were used in a fluid force production
context (i.e. lift and drag generators) before the advent of powered flight.
Under this sort of situation, we would predict that some kind of non-flight
mobility behavior was present, and that additional changes in morphologies
allowed a transition to full on aerial locomotion.
However, the precursor feathers might have, instead, attained some of the
relevant morphology under other forms of selection - for example, in the
context of display, brooding, armor, etc. Whether or not this is
"extraordinary" is a matter of opinion. What is not a matter of opinion,
however, is that observation that a pre-aerial phase would have existed because
the ancestors of flying maniraptorans were not aerial animals. Nothing evolves
with foresight; feathers didn't evolve "for" flight, they eventually obtained
morphology that promotes lift production, making them usable for flight.
Feathers must have obtained much of this morphology in non-flying animals.
> To repeat, having long light weight planar kites attached to ones arms
> would have an extremely debilitating effect of any other use of the
> arms... other than flight.
Based on what? You keep saying this, but you have cited no evidence at all.
You're only attempt was to suggest that living birds keep their wings folded
all the time when not flying, which is easily falsified by the observation that
literally dozens of other functions for wings exist, none of which are impaired
by the feathers - and in fact, many *depend* on having large, stiff feathers
attached to the forelimbs. You also haven't defined what "debilitating" means
here: are you talking about range of motion? Moment of inertia? Without a
specific set of physical parameters this is just arm waving.
Even the underlying concept of your argument seems odd to me. The flight stroke
is more kinematically complicated than almost any other forelimb behavior that
birds can engage in. So you are arguing that having long, light feathers
attached to the forelimbs would be "extremely debilitating" to more simple,
slow motions of the forelimbs, but magically not debilitating when the limbs
are moved rapidly through a series of complex positions during a flight stroke.
> Further, just as an aside, as far as I know, all birds that are
> flightless have evolved in response, small, ineffective, diminutive
> wings. So pick any alternative theory for their development that you
> wish, but you'll need to prove it since it would be highly unlikely.
The entire flight apparatus tends to reduce in secondarily flightless birds,
likely mostly because the soft tissue is expensive. However, you are not
correct that they all have "ineffective" wings. Flightless rails maintain both
some mobility and display functions for their wings. So do short-winged
grebes, for example. Domestic chickens use their wings as weapons. Practically
all flightless birds probably use the wings in brooding. Among flightless
birds, only ratites have wings that have virtually vanished (particularly
Kiwi). Galapagos cormorants have strongly reduced wings, as well. Otherwise,
some functionality often remains. And of course, this all ignores the other
group of flightless birds: juveniles of flying species. If you want to see how
their wings can be used in a non-flying context just check out the entire
career of Ken Dial. Or the recent work by his prior student, Ashley Heers.