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Re: Scientific American feathers paper




I assumed Alan had sent this to the list, not just to me - my bad. Here's the full message:


Glad you had a chance to see the paper. Let me see if I can answer the
questions you pose.

On Thu, 13 Mar 2003 12:31:20 -0600 "Tim Williams"
<twilliams_alpha@hotmail.com> writes:
>
> Nice stuff, not dumbed-down, with
> great
> illustrations that complement the text beautifully.

We fought with the editors over the use of a number of terms. It was
'dumbed-down' considerably in one draft. We did not meet or consult with
the artist who did the reconstructions. They are awesome, I agree. We had
considerable input to the diagrams as they were meant to be tied in
directly to the text. And, they had a lot to do with the readers
understanding of the stages. Remember a less dynamic, microscopic
description was available in the 1930's.
>
> .  (Alan, are you
> out there?
>   :-) )

Yes!
> First, a run-down of the individual stages.
>
>
the big idea here is, just as the structural genes and the feather
keratin proteins seem to be unique, the stages in development are each
adaptive in themselves. In other word there were a series of novel
structures and PROCESSES. Over time (and it was probably a relatively
short time in terms of generations) machinery and routines developed that
produced the variety of structures we now recognize as feathers


> According to the article, the hypothetical "Stage 3B" in feather > evolution > is essentially the structure of modern down feathers (plumules). My > first > question: If a down feather is a "jumbled tuft of barbs", what are > the > barbules there for? That is probably as good a description as possible for both natal down and much of adult down. Look at the figure, or, better yet, get some down from a pillow or jacket. The barbules may be absent, uncommon and without function, or may keep the barbs from twisting on one another. In any case, there are never very many, and they may simply be emergent features of the way the barbs are produced.


Does this second level of branching provide > extra > insulation? Perhaps not at this stage. But they are a consequence of the branching and growth processes.


> My second question also concerns the barbules. In Stage 3A+3B > (planar, > open, bipinnate feather), what is the adaptive utility of the > barbules?

Perhaps little except increasing the air trapping capacity of the feather

Do
> they provide coherence to the vane via some level of interaction
> between
> adjacent barbs?
Not until the pattern of growth changes slightly so that the barbules are
lengthened and the proximity of the adjacent barb is adequate for the
connection to occur. This will reflect changes in the timing of the
growth as the feather matures.


In other words, although the barbules do not yet > have the > hook+groove system to produce a tightly-closed vane, do the barbules > help > hold the barbs together in a planar structure.

Answer above.


> > Finally, is it possible that the presence of barbules in down > feathers is a > vestige of passing through a Stage 3A+3B (open pennaceous feather) > or even > Stage 4 (closed pennaceous feather)? In other words, modern down > feathers > are 'trimmed down' pennaceous feathers, not a more primitive > intermediate > stage.

Not necessary. Looking at the fossil record implies that the stages
appeared in roughly the same order in phylogeny as they do in ontogeny.
The most primitive feather is the filament on Sinosauropteryx, the most
basal of the feather bearing dinosaurs now known.
>
> Again, thanks for a great article.
>

You're more than welcome. It was surely my great pleasure.

Cheers,

Alan



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