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Re: Re.avian flight



> <<This is the way exaptations work: an adaptation allows the animal to do
something the adaptation wasn't designed for,
> and this use offers an advantage>>
>
> The adaptation is designed for *nothing*( and, in any case, the "thing"
designed fo something would be the character, and
> not the adaptation, that is instead how the character fits in the number
of way the omologous character was used by the
> predecessors of the animal in question); if the animal can "use" the new
character( and I think it always would, being the
> character not an extreme alteration, a deformation).

I don't quite understand this sentence...
I agree that adaptations aren't designed. A living being has a certain way
of life, a mutation appears, this way of life provides selectionary pressure
too keep this mutation, and afterwards the mutation is called an adaptation.
And adaptations like wing feathers (or limbs, for that matter, in the origin
of tetrapods) can be exapted for use in other ways of life.

> <<even though that use is not necessary for survival, it is just an
advantage>>
>
> Ok but it's a secondarily aquired ability;these birds were *already* able
to fly and *then* "learnt" that they could find fishes

Dippers hunt aquatic insect larvae.

> really better and farther than before( exaptation of the ability to fly);
this *doesn't* explain why they should have tried, once > caught their fish
, to get in the air, unless they were already able to do it and needed to
get home.

Remember the tail of *Archaeopteryx* that prevented it from gliding? Prey in
the mouth would have pulled the center of gravity forward and thus made
flight easier. As I have quoted Ebels, apart from a safe means of escape,
the ability to fly offers the opportunity to enlarge fishing ranges, among
other things.

> I mean, a mosasaurus trying to eat them would have been a good reason,
such as  any other kind of predator that wouldn't > have been able to eat
them once they were in the air, but this is one of the reasons for which
cursorial little theropods are
> thought to have "tried" to get off the ground (onto a tree, on a higher
rocky level, who knows?) .

Well, then, why has flight only evolved three times among vertebrates and
not three hundred times? Or, on the other hand, much earlier?

> Maybe an already semi-acquatic theropod , having the powerful wing
structure and the right movement needed to be able to > get in the air from
the water surface(selected as a mean of propulsion in the water), tried to
catch something in the air; this
> could be  not too difficult from a mechanical point of view( someone knows
something about  this?..I surely don't ) but yet, > why would you need an
explanation already considered as a possibility in the cursorial scenario??

"Tried to catch something in the air"? Very unlikely. There simply is
nothing edible in the air above large bodies of water; in the air above
small ones, there are the same insects as on the dry land around.

> <<My personal feeling is based on the evidence I gave -- what is your
evidence?>>
> I'm not surely the best person to provide you with all the possible
reasons considered to support the ground-up hypothesis, > but I seem to
recall some reports from the recent SVP meeting about some studies, one
regarding the ground-up( turning
> abilities given by the use of the tail and feathered arms[possibly two
different talks I don't remember]) and  one the trees-
> down( I would have to look for it in the archives, sorry).

Sounds quite unconvincing... I'll take a copy of the abstracts of this
meeting.

> However, I think your evidence, from the  point of view the possible
evolution of the aqcuatic lifestyle and the subsequent
> evolution of flight is not *yet* supported( this obviously doesn't mean it
can't be) by anything more than speculation
> (intelligent, but still such) and is therefore a  bit weak.

Well. All other hypotheses (trees-down, ground-up, ground-down) have serious
flaws IM and some other people's HO; if you can detect one in the hypothesis
I presented... and if I can't "discuss it away"...

> <<Ebel mentions a strong argument against ground-up -- chickens can fly
but don't like to do so when unnecessary>>
> a strong argument??
> Has he (or anybody else, if it's possible, but i think it will hardly ever
be) ever tried to compare the predatory pressure over > the different
populations of the different  "chickens" species(the wild
ones....galliforms[?], I don't know the name of the
> group comprising them all), trying to compare them with that under which
the little theropods considered to have been the
> first fliers evolved?
> I have the impression that domestic chickens would turn out to be, among
all their relatives(those living *not* in particularily > predators-free
enviroments) the ones with the worse flying ability.

The wild form of the domestic chicken that lives somewhere in South East
Asian jungles doesn't fly more.

I'm quite sure predator pressure hasn't changed much since the Permian or
so. Why should it have?

> If today's chickens were freed in the mesozoic in the region supposed(
always hypothetically speaking) to have been the
> place in which the litle theropods we're taking about lived(supposing it
had to be particularily different from other areas, but > I don't think it
would be necessaryto be so), i think they would have some more troubles
surviving  than those little , fast
> theropods, althought they are(the chickens) able to fly when necessary.
>
> I said this because I think using chickens as an example is totally
nonsense.

You know, ostriches and rheas have evolved flightlessness in environments
that were always full of predators. There are other means of escaping
predators, "flying itself is not worth striving for in any case", as Ebel
has put it.

> Anyway, I would be really interested in knowing the kind of enviroment
chickens' relatives( and all birds with an analogous > body structure and
possibly a  similar ecological niche) live in, their usual predators( and
occasional ones, if known) and
> how these populations are seen in their habitat complex; I mean, are they
usually rare  because the predatory pressure is
> high and only few can survive and reproduce, mantaining however a pretty
stable population?

In a jungle, hiding from predators is very easy.

> Again , back to the chicken analogy, I think it's pretty useless because
it represents an opposite "trend" if compared to that > considered for the
little theropods; chickens have secondarily adapted to a particular
lifestyle, while the supposed
> coelurosaurs were probabily in the same condition, but had never been able
to fly (yet)  but the predatory pressure would
> have selected the ones that had aquired the features needed to get in the
air(supposing the predatory pressure was the main > reason and not others).
>
> This obviously doesn't mean that taking off was the only way to survive ,
but justifies(or may justify, that is, from an
> hypothetical point of view the same thing) the selection of the features
needed to begin to fly(or jump higher, maybe on some > tree branches;-).

Yes. Of course. But this doesn't explain in any way *how* "the features
needed to get in[to] the air" *evolved*, just *why* they were usually
*maintained* after having evolved, and, see above, even this argument has
loopholes.

> I'm sorry for the long post;

C'mon. I'm the one who has probably written the longest post in the history
of this list. :-]