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

[dbensen <dbensen@gotnet.net>]

>>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.<<
There is a very good reason for this, but it is not functional, but phylogenic.
Bats, pterosaurs(we assume), and gliding lizards all evolved from QUADRIPEDAL
ancestors.  However, the ancestors of birds were most probably BIPEDAL.  For a
quadraped, skin flaps between the legs make sence, they act as a parachute (look

at cats), but a bidpedal animal like a small dinosaur would have to rotate its
legs outward at the hip socket (which they couldn't do)  for such a trick to
work.  It was much easier to evolve controll surfacase on the arms, which would
swimg forward while the animal was jumping anyway, and the tail.  If birds had
evolved from quardribeds, the would look sort of like feathered, beaked bats,
and woulnd't be nearly as appeling (though I suppose we wouldn't notice).

Matthew Bonnan wrote:

> 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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