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Re: bauplan convergence

In a message dated 6/16/00 9:50:04 PM EST, kinman@hotmail.com writes:

<< I see no big problems with such a sequence, but I believe  protofeathers 
first evolved for either display or insulation, not both at  the same time. I 
would suspect that display came first, and insulation would have eventually 
begun to reinforce that.  Then the aerodynamic developments followed. >>

Neither display nor insulation provides a >primary cause< for the evolution 
of feathers. When an organism has no feathers, it cannot use them for 
display, for brooding, or for insulation(!). This would require the organism 
to predict the future (e.g., "I will need insulation and to show off, so I'll 
evolve feathers"). Rather, the first feathers evolved for some other reason, 
and as soon as or very shortly after they appeared, they would have found 
secondary uses (exaptations) for display or for insulation (or for 
parachuting). But the primary cause must have been something positive and 
internal. The best suggestion I've read so far is that feathers appeared as a 
means of sulfur excretion through molting. Excess sulfur is used up in the 
keratin proteins of the feathers, which are shed from time to time during the 
animal's life. The excess sulfur itself may have resulted from a metabolic 
shift toward homeothermy in the archosaur lineage.

See: Reichholf, Josef H., 1996. "Die Feder, die Mauser und der Ursprung der 
Voegel," Archaeopteryx 14: 27-38.