Re: Glideing, flapping

[Nick Longrich <longrich@phoenix.Princeton.EDU>]

My personal feelings on the whole ground up ground down thing is that
gliding makes sense because everything does it. Snakes, two or three lines
of marsupials, two lines of rodents, the colugo, Kuhl's gecko, Draco
volans, extinct forms like Sharovopteryx(= Podopteryx) Coelurosauravis,
Kuhneosaurus, Icarosaurus, etc. etc. 
        This means that this is a path that is commonly taken by
animals. And basically, it solves a big problem: how do you get wings?
By successive, incremental enlarements of skin/scale/whatever until it
is large enough to substantially slow your fall, then you start moving
forward more than you move downward, and the you start generating lift.
Flapping is just an add-on here. The purpose of flapping motion is to
generate forward thrust, by generating forward thrust with the distal
part of the wing (and some lift) the air passing over more proximal
parts of the wing can generate more lift. 
        It's nice and incremental, the way evolution tends to work (I'm
a Dawkinist rather than a Gouldian). 
        On the other hand, nobody has any examples of small, terrestrial 
leapers evolving flapping in today's world. As for the "well, if
gliding's so common, how come there aren't more fliers", my little
parable is mountain climbing: maybe it's really easy to get halfway up
the mountain because it's got mild weather and a shallow slope, but a
real trial to get all the way up. There is no reason to assume that
simply because there are a lot of gliders that they ought to all evolve
flight. 
        Yes, and I forgot the frogs and gliding snake. Anyways, that's my 
take on it.

Tracy wrote:
> 
> Why even have a glideing phase? Why not just go streight to flapping? Snakes, 
> haven't developed wings, nor frogs, nor lizards, etc. If an animal glides 
> well, why would it even have to start flapping.
> 
> To be even more contraversal, birds went from the trees down, while 
> pterosaurs went from the ground up. I'm still under the subspection that 
> pterosaurs never went into the trees (Boy, talk about your Heresies!!!)
> 
> Tracy
> 
> 
>