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




--- On Thu, 9/25/08, Tim Williams <twilliams_alpha@hotmail.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'
> component.

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 
step-wise evolution...

> 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 
booger...

Don