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Re: birds scales



>I think the point being made is that a feather is simply a modified hair.  The
>real question is what were the steps taken to make this transformation?  If we
>assume for a moment that this hair was pretty much undifferentiated until the
>first aboreal theropods arrived, we could conclude that this modification
>occurred to help the animals travel from branch-to-branch, or tree-to-tree.
>Here's a possible evolutionary path: Hair -> Down -> Feather.
>
>Questions, comments, snide remarks?
>
>ROb

No, a feather is NOT a modified hair.  Mammalian hair was a separate
development of structures that appeared between reptilian scales.  Feathers
may (or may not) have been scale derivatives - Alan Brush is the expert here
- but are NOT homologues to mammalian hairs.  We have no idea, of course, if
feathers are homologues of pterosaur or Pelecanimimus "hairs".  It may
simply be that different lines evolved "hairlike" structures as adaptations
to temperature control (as have bumblebees, for example) and that
convergence to a hairlike form is common.

Also - down may represent a derived, not a primitive, condition.  If
feathers started out as extended bladelike structures (Alan??) the
development of a pinnate structure built around a central thickened blade
may have been the first development (as happens with many featherlike
structures in nature - palm leaves, for instance).  Forms like down,
filoplumes etc - even bristles - may be modifications of that structure.
Just because down looks less structured than a flight father doesn't mean it
is more primitive.
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
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