> While the lack of scale plasticity in extant birds may very well be
> a derived trait, I still can't help but wonder about the old "party
> line" regarding why scales were lost in the first place (i.e. the
> weight reduction hypothesis). With the exception of osteoderms,
> scales are not that heavy. Birds get away with flying around with
> all kinds of strange display structures that would weigh more than
> a light covering of scales would.
Some might argue that that is what birds can afford to do, after they
first got good at flying around.
You can put carpets and chairs in modern planes (even small ones),
but the Wright Flier had to watch how much material it took on
board.