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Re: DOWNY STEGOSAURS



--Original Message-- From: archosaur@usa.net Date: 15 October 1998 03:34



>Isn't it strange that in pterosaurs, arthropods and mammals all the
insulating
>covering is fur, yet in birds it is feathers?
>
>If fur is the evolutionary default, then deinosaurs should have grown fur
if
>they were endothermic, but they didn't.

They did.  They grew "Sino-fur".  You may call that protofeathers, or
branched fur, but the latter is simply a variety of insulating fur.  The
branching may well have led to an increase in density beyond the branch
point, and air pockets above the skin, contributing to the insulation
properties.  Who's to say the original wasn't similar to the unbranched
mammalian structure (though not necessarily homologous).

>
>It seems that some evolved a type of feather, perhaps even evolving
feathers.
>Why is that?

>
>Well if insulation isn't why birds evolved feathers, then what else do we
>have.
>
>There's the aerodynamics of it. Of course the evolutionary default for
>ornithoptering is a membranous skin. Not feathers.


"Default", yes, but not a hard and fast rule of course.  Feathers were "more
difficult" to evolve maybe, in some sense, and "less likely", but not
impossible.  It just makes it less likely to have happened twice.

>
>Again feathers might have been some strange twist on the same formula. It's
>happened before. But there is still something bothersome about that. It
just
>doesn't seem like that is a plausible reason to evolve feathers.

Aerodynamics not a plausible reason to evolve feathers?  !!!!!!!!!
??????????

>
>Fur had already proven itself a fine insulator, so why feathers.


Fur is used for aiding the parachuting effect (colobos monkeys eg.), and
steering (squirrels eg.).  I think this is undeniable.  It is also
undeniable that feathers would suit this purpose even better.  Most people
could imagine branched fur fibres evolving into feathers.

>Well what else are feathers good for. Think cockatiel, peacock, umbrella
>birds, etc.
>
>All these birds use their feathers for display purposes. Now reptiles have
>developed all kinds of freaky display appendages to them. And since
feathers
>are modified scales, it would seem plausible that the original use of
feathers
>is for display purposes, not endothermy, nor aerodynamics.

Skin and scales can also be used for display purposes.  Any advantage
feathers might possibly have for this purpose doesn't compare with their
aerodynamic advantages.


JJ