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Re: Feathers vs patagia




David,
Well, I do look forward to seeing your paper. I love new ideas. However, I'm not sure your objections to Larry's ideas are necessarily valid. He isn't saying that birds evolved from any of the advanced pterosaurs you are describing, but forms which were far more primitive which haven't been found (or perhaps sitting unrecognized in some museum drawer).
I can contemplate such an ancestral form (perhaps a little more pterosaur-like than birdlike) gliding from gymnosperm to gymnosperm (be they cycads, conifers, or some other gymnosperm). One line goes the pterosaur route, another goes the bird route, and the intermediates go extinct. And if I understand Larry's ideas correctly, theropods are secondarily flightless birds (in agreement with BCF theories).
I don't know if pterosaurs and birds had a primitive gliding common ancestor, but I think it is a good idea to investigate such possibilities (just as you are apparently doing in developing some other possible scenarios). Whether Larry is wrong or right, I don't think his reasoning is teleological, at least in the ways you seemed to be pointing out. If they do have a common gliding ancestor, I suspect it would be more pterosaur-like than birdlike. Anyway, looking forward to your paper.
-----Ken
*******************************************************
From: "David Marjanovic" <David.Marjanovic@gmx.at>
Reply-To: David.Marjanovic@gmx.at
To: "The Dinosaur Mailing List" <dinosaur@usc.edu>
Subject: Re: Feathers vs patagia
Date: Sat, 6 Jan 2001 14:26:16 +0100

> >The arboreal hypothesis has a few big problems. One is the transition
from
> >parachuter to glider (not actually necessary) and the transition from
> glider
> >to flyer (necessary). Why don't birds have ordinary patagia? Pterosaurs
had
> >hair (or was it dinofuzz???) and developed patagia instead of wing
> feathers.
>
> (snip)
>
> Perhaps birds started out with larger patagia. It is my opinion that
> feathers developed initially for better insulation. Contour feathers would
> have been an improvement over hairlike protofeathers. Also, a large
> patagium would have contriburted to heat loss. Another advantage would be
> that a feathered wing could beat more rapidly, due to the fact that air
> could slip through the feathers on the upstroke.


I'm afraid that unless you introduce teleology pterosaurs won't lose their
wing membranes (and the wing finger) and later evolve feathers. Also be
aware that pterosaur wings aren't simply skin like those of bats (or the
pro- and metapatagium of birds). They are greatly stiffened by protein rods.
Furthermore, they're not as well vascularized as bat wings (and maybe even
furred), which would have cut down heat losses enormously. (Bats use their
wings for cooling: the hot blood from the flight muscles flows into the
wings and dissipates heat there. Pterosaurs and birds [all Ornithodira, I'd
say] have a different cooling system -- air sacs -- and therefore keeled
breastbones: to prevent the air sacs in the flight muscles from collapsing.)
I can't imagine any situation that could lead pterosaurs to lose
their sophisticated wings and evolve new ones. Advantages to be gained from
these new ones just aren't enough.


> This more rapid wingbeat could enable a hovering type motion, and enable
> relatively soft landings on hard perches that gymnosperms would offer. (I
am
> assuming these were predominant trees in a colder enviorn). Pterosaurs
seem
> more likely to have made more clumsy landings on more flexible Cycad
> branches.


Cycads are gymnosperms; you're talking of conifers, aren't you? Conifers
were the dominant trees quite everywhere, as cycads don't grow very high. I
don't think that pterosaurs routinely (if ever) landed on trees. All species
found so far (preservational bias, I know) lived near water and landed on
beaches and on water.
Hovering, good manoeuvering and slow flight are impossible if the
wingtip vortices are too chaotic. There are 2 ways to get around this
problem: 1. the way pterosaurs did it: to elongate the wing tips enormously;
2. the way ornithothoraceans do it: to develop an alula. *Archaeopteryx* and
confuciusornithids suchlike lacked alulae and therefore many special flight
skills.


I just don't by your hypothesis that birds are pterosaur descendants (have I
got it right? I've forgotten the URL of your homepage...); it is better than
deriving birds from *Megalancosaurus*, but still all evidence is against it.


How do all those feathered non-avian theropods fit into your hypothesis,
BTW?

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