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Re: Science feather strength debate



> > If you can power the downstroke, the upstroke (back to
> horizontal) should take care of itself, what am I missing?
> 
> 
> Apparently the humerus must be lifted above the horizontal
> in order to
> achieve a recovery stroke.  This is according to
> Rayner (in the Ostrom
> Symposium Volume) although this is not the only source.

If the wing is generating lift, and the bird has just completed a downward 
stroke, would not the wings rise back up? In a fixd wing aircraft, if your wing 
spar is too weak, and snaps, the wings "fold up"
 Sure, powering the up stroke could increase the flapping rate, and provide 
forward thrust too, but I can't believe it if flapped its wings down, that its 
wing would just stay that way, with massive anhedral.
I don't see the lack of a powered upstroke as a convincing argument against 
some form of flapping behavior (I can see it as an argument about the upper 
limits to what sort of power it could get by flapping)

 
> > The presence of a keel, indicates the forelimbs were
> doing something that required more power than could be
> delivered without the keel.
> 
> 
> BTW, although _Confuciusornis sanctus_ (the type species)
> has a keel,
> other confuciusornithids (such as _C. dui_,
> _Changchengornis_ and
> _Eoconfuciusornis_) do not.
> 

So what can you say about the differences of those others, as far as 
environment, or morphology.
Not knowing anything about the others, I could engage in pure speculation that 
maybe the others lived in areas more conducive to soaring, and confuc. lived 
where the soaring wasn't so great, and often needed to supplement its flight 
with some of its own power (hence the keel)


> I take your point.  However, it now appears that many
> elements of the
> flight apparatus arrived by a process of exaptation. 
> In other words,
> they original had other (non-flight) functions, and took on
> a role in
> flight.

Of course, it now seems feathers were obviously exapted for flight from earlier 
"fuzz" that served as insulation (possibly with a display intermediate)

ons, and I've heard all of their functions proposed as the original role in 
para-aves.
(aerodynamic surface, insulation, display)

I don't see what other function a keel could serve, other than to power the 
forelimbs as they are moved toward the chest.
Its easy to imagine early feathers insulating, and not used for flying.
Strong forlimbs muscles to bring forelimbs sporting a large area, "down" 
towards the chest.
Sounds to me like the most obvious effect of that is something like a flap

> Maybe the expanded pectoral muscles were used to help
> _Confuciusornis_  climb up tree trunks? 

Sort of like hugging the tree tight to get a grip? Do we have any other example 
of something like that? seems to me that squirrels can sufficiently grip trees, 
without prehensile hands, or a keel.

> After all, the hindlimbs were poorly adapted
> for climbing, so the forelimbs might have been forced to do
> most of the work.

How would that work- give the tree a tight bearhug with your forelimbs... 
and.... ????? I can see it working for holding on, but not actually climbing, 
and if it could climb without clamping on with both forelimbs powered by 
muscles attached to its keel, why would it need the "keel clamp" forelimbs?
>From what I gather, the manus doesn't exactly look adapted for getting a good 
>grip either, does it?

I just don't have a good enough imagination to see a possible other use for 
forelimbs like it had, that would require the power provided by a keel.
Flapping still seems like the best explanation, despite lacking a powered 
upstroke.

> 
> 
> > If it had all these flight adaptation, but yet still
> was incapable of powered flight.... what were those
> adaptations for? that seems like an awful lot of adaptation
> for
> > gliding between trees
> 
> 
> That's assuming it glided between trees.  Maybe
> _Confuciusornis_
> glided from trees down to the shore, or into shallow
> water?

Well, thats sort of my whole point.... considering what other things it could 
do with gliding, other than saving some climbing and walking be
 than enough adaptations to allow it to ridge soar in conditions presently 
found in many places.
It (and its ancestors) might have been becoming quite comfortable "on the 
wing", while still being gliders.

I was prompted to "chime in" on comments that this thing was a glider, 
therefore it was more comfortable on the ground, and not in the air (that, and 
that as a glider, it would need elevation to launch, and therefore likely 
climbed trees).

I see what I think are two bad assumptions:
1) Being incapable of completely self powered flight means the forelimbs likely 
didn't function as wings like they do today
2) Because it was a glider, its glides started from trees or some other place 
that requires climbing to get to (as opposed to merely a shallow slope, or 
completely flat ground in front of a slope, or the top of a bluff/dune/ shallow 
ridge, that pretty much anything that walks can ascend)