Re: [RE:Origin of feathers]

[archosaur@usa.net]

Interesting, but aren't there fossil birds that show lack
of blood channels in the bones. Thus indicating that early birds were 
ectothermic.

Archosaur J
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> 
> Perhaps we should pause to remember that the debate over arboreal v   
> cursorial origin of flight and feathers goes back more than a century to   
> O.C. Marsh (1880) and S.W. Williston (1879.)  Marsh's arboreal argument   
> was carried forward primarily by Heilmann (1926) who argued against   
> cursorial origin of avian flight and concluded that feathers were   
> elongated scales which evolved for aerodynamic purposes and were   
> advantageous in parachuting and gliding. Although some still argue   
> Heilmann's theory today, one of the principal contemporary advocates of   
> the arboreal origin of flight, Walter Bock, abandoned in 1986 the   
> "aerodynamic origins" theory of feather evolution in favor of P.J.   
> Regal's idea that feathers evolved for insulation in protobirds that were   
> facultative homoeotherms. Regal concluded that avian feathers and   
> homoeothermy were probably fully evolved prior to even the most   
> rudimentary flight.
> 
> In the absence of any undisputed fossil evidence of protofeathers, I   
> prefer Regal's theory on the evolution of feathers over Heilmann's not   
> only because I think it has more intuitive appeal, but partly because it   
> is independent of the arboreal/cursorial problem concerning the origin of   
> flight. Accepting Regal's theory means you can have homeothermic   
> feathered creatures that, whether on the ground or in the trees, are   
> preadapted to responding to selection for gliding and flight.
> 
> Williston's theory of cursorial origins of flight were carried forward by   
> Baron Franz Nopsca (1907, 1923), John Ostrom (1970's-80's) and a   
> fascinating (at least I think so) 1983 article by Caple, Balda and Willis   
> [Am. Nat. 121:455-476.]  Despite the attractiveness of the trees down,   
> parachuting - gliding - flying scenario, I lean towards Ostrom's and   
> Caple's cursorial theory--particularly if combined with Regal's theory on   
> the evolution of feathers.  The initial aerodynamics-related selective   
> pressure on feathers on the trailing edges of the arms of a   
> homoeothermic, feathered proto-bird would be towards reduced drag and   
> increased lift and thrust. Although the "ground up" argument is not   
> without problems, it is also appealing to me because it seems to   
> eliminate at least two evolutionary steps required by the "trees down"   
> theory--tree dwelling and parachuting.
> 
> Reasonable people have disagreed on these issues for a hundred years and   
> will presumably continue to do so--at least until the evidence is in.


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