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Fw: Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)



-- On Sat, 9/27/08, David Marjanovic <david.marjanovic@gmx.at> wrote:

> > Sure. And/or accidental collisions while gliding from
> tree-to-tree, 
> > leading to hawking and echo-location.
> 
> *Onychonycteris* already had flapping flight and lacked
> echolocation.

True enough. Yet O. (and ancestors) acquired flapping flight through a gliding 
phase, apparently. The point was that the feasibility of an incremental 
gliding-to-flapping transition in bats isn't hard to understand when you 
consider that 'accidental' insect/bat encounters would occur while gliding 
tree-to-tree. The probability of such encounters occurring on any given glide 
at any given insect density can be graphed, given reasonable assumptions about 
speed and length of glide. 

> > The space between the trees was presumably
> under-exploited by 
> > insectivorous birds at night. Hence the success of the
> bats at moving in.
> 
> Yes, and apparently it still isn't completely full.

And how full of birds/bats is too full, when you are a glider competing against 
fliers?

> >> > Quite correct. Acquiring prey by gliding
> simply
> >> isn't going to work when birds are around, but
> commuting
> >> is always an open option if you have a job to go
> to...
> >>
> >> Again, an apparent contradiction.  If obligatory
> biped Don
> >> Ohmes can encounter flying insect populations in
> his
> >> tree-to-tree excursions (presumably terrestrial) -
> why are
> >> these same hordes of insects beyond the reach of a
> modern
> >> aerial glider?
> >
> > Competition. Unless you know of an insectiferous
> arboreal environment that 
> > is presently free of bats and birds???
> 
> "Free" is not necessary. You use the word
> "underexploited" above...

I don't think an "incipiently flapping glider" could maintain a lifestyle 
wherein "incipiently flapping" was advantageous, in the presence of birds, due 
to competitive constraints. Therefore, the lack of extant "incipiently flapping 
flyers" does not imply that the 'mechanical hurdles of the passive-to-active 
transition are insurmountable, or so difficult as to make "tree's-down" 
inherently unlikely', implying that "ground-up" is more likely. That was the 
assertion made, if you want to check the context by re-reading the thread.

> >> > Also, the debate IS a dichotomy in the sense
> that you
> >> HAVE to start somewhere. Once the ball is rolling,
> the
> >> dichotomy disappears, but that first step is is a
> >> > booger...
> >>
> >> Yes; but the "first step" is not
> dictated by
> >> relative ease.  Natural selection can only act on
> what's
> >> already available.
> >
> > Exactly! On the gravity-driven side, you have every
> animal that can or 
> > will leap, fall, or pounce from a high place for
> natural selection to act 
> > upon. On the muscle-driven side, ya got nothing but
> your imagination and a 
> > long list of "ancestral constraints". As any
> manufacturer can tell you, 
> > the availability of feedstock and ease of manufacture
> all count when 
> > assessing the likelihood of success.
> 
> "Every animal that can or will leap, fall, or pounce
> from a high place" may 
> _not_ include the ancestors of birds. That's our very
> point.

No, 'their' point is quite different, as I mentioned immediately above. 

BTW, I was arguing the plausibility of a cursorial flight origin before you 
learned to read, and have to often posted such to DML. I am well aware of that 
possibility. In any case, my point about what is "readily available for natural 
selection" stands.

> >> In other words, it makes no difference if gliding
> is
> >> "easier" than leaping upwards to catch
> insects, if
> >> the former behavior never existed in the ancestors
> of birds.
> >
> > I did not realize the the non-existence of gliding
> behavior in proto-birds 
> > had been proven...
> 
> Did you overlook the "if" part?

No, I did not.

> That said, the fact that the tertials of extant birds are
> not simply 
> remiges, but lengthened contour feathers that are not
> anchored to the 
> humerus, and the fact that *Archaeopteryx* apparently
> lacked tertials 
> altogether and thus had a fairly broad gap between wing and
> body, _does_ 
> argue _strongly_ against any kind of gliding phase during
> the origin of bird 
> flight. (And that's ignoring the practically complete
> lack of climbing 
> adaptations in all known animals around that origin.)

I disagree. All flapping birds can glide. Are you implying that Arch had no 
flight capacity at all? The gap between wing and body is a trivial matter, IMO. 

Also, "practically complete lack" does not equal "lack" of climbing ability. 
Having some familiarity w/ cycads, I conclude that climbing them was no great 
chore for Archie, and I assume, even less so for Archie's ancestors.

> > I would also recommend avoiding the poker table,
> although that might be 
> > good advice for everyone in any case. :D
> 
> Are you aware that " :-D " means you are
> laughing? Not smiling, not 
> grinning, but laughing?

Absolutely. LOL, dude, LOL.

Don