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Re: vaulting pterosaur launch, questions


Not necessarily - especially if the emphasis is on maneuverability
during the
descent. Sure, mammalian gliders and many reptilian ones (like _Draco_ and
kuehneosaurs) have a continuous lift surface that connects the body wall to the
limbs. But the distal gliding surfaces (webbed feet) of "flying" frogs
(_Rhacophorus_, etc) and "flying" lizards (_Ptychozoon_) accord a great deal of
benefit in gliding. True, in _Ptychozoon_ the cutaneous flaps play a role too;
but those big webbed feet improve both the lift:drag ratio and maneuverability.<<<

True enough, although those taxa have torso's that are dorsoventrally flattened, allowing the stomach (and the tail in Ptychozoon) to be utilized as airfoils, and ones that have substantially more surface area than the webing of the digits. In addition both Ptychozoon and flying frogs show adapations for aboreality. Niether of these applies to Archaeopteryx, and I think those are fairly key elements of that particular analogy.


Even the brooding hypothesis (which I like) doesn't explain why the
feathers of _Archaeopteryx_ were asymmetrical,

It does, or at least it claims to do: the leading edge is more
likely to
contact the ground.

Hmm... do you really 'buy' that explanation?

I don't personally, but it hasn't been falsified. Certainly it's more reasonable than invoking pancaked arboreal frogs and lizards as an analogy for gliding in Archaeopteyrx.

However, the lack of tertials in _Archaeopteryx_ does not 
necessarily mean it didn't glide, nor that
its ancestors didn't either.<<<

I can't agree with the first half of that statement, but you're certainly right that it doesn't rule out the possibility that a gliding stage preceeded Archaeopteryx. There just isn't any evidence for it.


Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com


-----Original Message-----
From: Tim Williams <twilliams_alpha@hotmail.com>
To: dinosaur@usc.edu; twilliams_alpha@hotmail.com
Sent: Mon, 16 Jun 2008 9:24 pm
Subject: RE: vaulting pterosaur launch, questions
Not necessarily - especially if the emphasis is on maneuverability
during the
descent. Sure, mammalian gliders and many reptilian ones (like _Draco_ and
kuehneosaurs) have a continuous lift surface that connects the body wall to the
limbs. But the distal gliding surfaces (webbed feet) of "flying" frogs
(_Rhacophorus_, etc) and "flying" lizards (_Ptychozoon_) accord a great deal of
benefit in gliding. True, in _Ptychozoon_ the cutaneous flaps play a role too;
but those big webbed feet improve both the lift:drag ratio and maneuverability.<<<

True enough, although those taxa have torso's that are dorsoventrally flattened, allowing the stomach (and the tail in Ptychozoon) to be utilized as airfoils, and ones that have substantially more surface area than the webing of the digits. In addition both Ptychozoon and flying frogs show adapations for aboreality. Niether of these applies to Archaeopteryx, and I think those are fairly key elements of that particular analogy.


Even the brooding hypothesis (which I like) doesn't explain why the
feathers of _Archaeopteryx_ were asymmetrical,

It does, or at least it claims to do: the leading edge is more
likely to
contact the ground.

Hmm... do you really 'buy' that explanation?

I don't personally, but it hasn't been falsified. Meanwhile, we are invoking pancake frogs and lizards as an analogy for gliding in Archaeopteyrx.


However, the lack of tertials in _Archaeopteryx_ does not 
necessarily mean it didn't glide, nor that
its ancestors didn't either.<<<

I can't agree with the first half of that statement, although you are right that it doesn't rule out the possibility that a gliding stage preceeded Archaeopteryx. There just isn't any evidence for it.