Gliders to Fliers? (Was Re: Ruben Strikes Back)

["Matthew Bonnan" <mbonnan@hotmail.com>]

Dinogeorge said:
It is >much< more likely that flight evolved in small archosaurs that
> adopted an arboreal lifestyle and stayed small until true flight evolved in
> their clade, taking full advantage of light weight and gravity assist for
> gliding.

Okay, George, I've somehow misconstrued your hypotheses on dinosaurian 
evolution before, so if I do it again here please try not to take offense. 
=)

My question for you, or anyone else on the list, is this: all the gliding 
animals I am familiar with incorporate both their forelimbs AND hindlimbs in 
the act of gliding.  Flying squirrels use a patagium which spans from fore 
to hindfeet.  Gliding lizards have a sheet of skin/scales that stretches 
between the fore and hindlimbs.

Now, both bats and pterosaurs have a patagium-like structure which also 
stretches fore to aft.  I no very little about proposed mechanisms for bat 
or pterosaur evolution, but I can swear that in both groups it has been 
proposed that they developed flight from gliding organisms (corrections to 
me please if I have this mixed up).

Pterosaurs would seem to be ideal candidates for a trees-down glider 
evolutionary sequence because they apparently incorporated both their fore 
and hind limbs in flight.  See where I'm going?  As Gatesy, Padian, and a 
number of other folks have pointed out, the forearms of birds are decoupled 
from their hindlimbs.

If birds are descendants of small arboreal archosaurs (dinosaur, 
non-dinosaur) which were gliders, how do you think the decoupling of both 
the forelimbs and hindlimbs took place?  Am I missing something: are there 
gliders which do not use both limbs with a sheet in between?

Just curious, and you know what they say about curiosity and that cat. =)

Matt Bonnan

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