Bird flight once more (was Re: What is a Dinosaur? and semilunate carpal)

["David Marjanovic" <david.marjanovic@gmx.at>]

> << Wait a minute. There have _never_ been any _bipedal_ predators other
than
>  theropods, most or all of which have (had) very stable hands. >>
>
> How about >people<?

People have become predators more or less yesterday, and have always used
>weapons<. A totally unfair comparison.
BTW, as I said it isn't necessary to have stiff wrists, it just helps.

> << In BCF birds (sensu BCF) begin to fly, then evolve stable wrists, and
in
> the
>  meantime they have flown by magic? Or by means of _enormous_ muscles on
> their forearms? >>
>
> No, they didn't fly very well at first. They just fluttered to break their
> falls. When their hands/wings began to stabilize, they flew better. Why
fly
> at all? It helps to solve the Falling Problem for arboreal animals.

Assuming that the ancestors of birds _were_ arboreal.
I'd expect a _parachuter_, like "flying" frogs and snakes, for solving the
Falling Problem, not a _flier_. (Gliding is IMHO the better form of leaping
_from branch to branch_.)

> It doesn't solve >any< problem for cursorial, ground-dwelling predators;
> ground-dwellers have no need to fly, consequently flight adaptations are
not
> useful to them and are not usually selected for in their evolution.
> Consequently ground-dwelling animals are extremely unlikely to be directly
> ancestral to flying animals outside the arboreal paradigm. If the
evolution
> of flight from ground-dwelling animals is so plausible, why don't pigs and
> kangaroos and people have wings?

You know what, here I happen to _agree_ with you. :-) Flight may solve
problems for flightless dipper-like animals -- the ability may come nearly
by itself.

> << In the "standard theory" (judging from this list it consists of
> hundreds of competing hypotheses) there is a function that can be
performed
> without stiff wrists but works _better_ with stiff ones, so when stiff
> wrists evolve -- of course by chance, as mutations happen -- they bring a
> selective advantage. >>
>
> That's the kind of tautology that fails to drive the standard theory.
"Well,
> stiff hands must have been useful to them, otherwise they wouldn't have
> evolved them."

Exactly not, I repeat. "Well, stiff hands evolved, and were retained because
they happened to bring an advantage." There are plausible ideas about what
this advantage may be (holding big strong prey, carrying meat to the nest
with less effort), and, well, if stiff hands had not been useful they would
not have been retained and wouldn't show up in the fossil record, except
maybe in one individual that would be regarded as pathologic.

> Useful how? They were certainly useful when it came around to
> acquiring wings, but what about when wings were still way off in the
future
> of possibilities?

Then they _had_ absolutely nothing to do with flying. See above.

> But if they already had a marginally useful wing

Marginally useful wings are those kinds of things that are _not_ useful. Oh,
an adaptation to parachuting? I can't rule that out a priori, but then I
have to ask how in the world did a parachuter evolve into a flier.

> that would be improved by
> being stiffened,

that would, probably, have to _be_ stiff from the very beginning. (Probably
testable, but not easily.)

> A vertebrate wing isn't going to evolve by random
> chance; it's too complicated a structure.

But by successive exaptations. Just like lungs, digits, insect wings and
lots of other features.

> It's not going to evolve as a set
> of randomly acquired, undirected characters that just happen to assemble
> themselves into a wing, any more than a shattered cup will reassemble
itself
> when you throw the pieces back onto the table.

Of course not. Have you had the opportunity to read the still-unpublished
Hopp & Orsen Dinofest 1998 paper? (If not, ask them for it.) Wings can
easily have evolved (on an already feathered animal, contra BAND) for
brooding -- and here marginally longer feathers _in the exact right places_
mean marginally more room for eggs means directly more offspring. It can
hardly become more Darwinian. Then, over the millions of years, one such
animal evolves into a fish eater. I'm sure you agree that this can happen.
For this it is useful to be able to swim; how would such an animal (still
flightless) have swum? Not with its tail (too thin and stiff), not well
enough with its legs (wrong shape, wrong position, not webbed), but probably
with its wings. This should produce the wingstroke. Now you have basically
something like a dipper. It doesn't evolve into a penguin because maybe it
still needs its wings for brooding (unlike penguins); maybe there is no free
niche for it in large bodies of water (plesiosaurs etc. galore); maybe it
lives only in small mountain rivers (like a dipper) where there are no lakes
or sea. If it just flaps faster it can continue its underwater flight in the
air. This is faster than underwater and allows e. g. fast exploitation of
new hunting grounds -- it brings an advantage. (*Archaeopteryx* may be such
an animal that happened to live at the seashore.) No more random than usual
in evolution. Just first feathers, then wings, then the wingstroke, and then
flight, not all that at once.