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RE: Campbell's even crazier than a MANIAC? (archeopteryx climbing)
--- On Thu, 9/25/08, Tim Williams <email@example.com> wrote:
> Also, the inception of flapping should not be assumed to be
> equivalent to "moving in the direction of powered
> flight". In order to be selected, this behavior
> (gliding+flapping) should be beneficial in its own right,
> rather than just be a stepping stone to flapping flight.
It (gliding+flapping) is only viable if there are no flappers around that can
glide whenever they want to.
> There is a swathe of empty morphospace available to gliders
> who want to engage in occasional flapping. This
> ecomorphology would put them outside the vast morphospace
> currently occupied by flying vertebrates (birds and bats).
Yes, but there is nothing to eat there now, which is why it is empty...
> It'd be interesting to know what circumstances
> led to the gliding-fluttering flight inferred for
> _Onychonycteris_ (the most basal known bat), given that lack
> of echolocation would make aerial hawking behavior highly
> unlikely. _Onychonycteris_ seems to be have been very
> well-adapted to life in the trees (especially scansorial and
> suspensory behaviors), so there's little doubt that the
> evolution of flight in bats had an 'arboreal'
I am guessing the level of competition was very important; ie, lots of fat,
slow bugs, and nobody faster or better positioned than _Onychonycteris_ (and
presumed ancestors/kin) to eat them.
My personal best-guess cartoon re bat evolution has lack of competition in the
field of nocturnal insect-catching as a key plot element. I have been places
where flying insect populations are large enough that one is bound to encounter
a few on any straight-line tree-to-tree excursion. Makes a good base-line for
> I don't see things quite the same way. The paucity of
> gliding predators may have more to do with the paucity of
> specialized arboreal predators, and/or the demands imposed
> by predation and using the forelimbs for prey capture
> (damage to the patagium by struggling prey; reduced mobility
> when chasing prey when the fore- and hindlimbs are joined by
> a patagium; etc).
These are problems intra-specific selection can solve if there aren't lots of
other species around who have already found solutions.
> Most extant gliders are 'just moving from
> tree-to-tree' because that's what gliding is for in
> these taxa: for commuting.
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...
> > BTW, are there ANY cursorial vertebrates currently
> "moving in the direction of powered flight"?
> None that I can see. So that's zero cursorial
> vertebrates currently "moving in the direction of
> powered flight"? Thats' the same number (zero) as
> arboreal gliders currently "moving in the direction of
> powered flight"? So it's a level playing field.
A key step in the path to flight is the manifestation of lifting surfaces, and
a number of (taxonomically diverse) animals on the gravity-driven path have
taken that step.
There are (apparently) NO animals on the muscle-driven path that have made any
noticeable progress whatsoever, be it lifting surface or flapping power...
That is hardly a level playing field, and I say that as one who is quite
receptive to muscle-driven flight evolution scenarios, at least w/ birds.
Heh. Locate one of your neighborhood cycads, and look at the trunk. A smallish
animal that can't climb that, cannot climb ANYTHING. And even a small pig could
"perch" in the rosette.
So I continue to maintain that the obvious "terrestrial-ness" of Archaeopteryx,
et al, is not necessarily key to the gravity vs muscle power debate.
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