Re: [Combined answer: Feathered/scaly theropods: trying to make the point.]

[Ronald Orenstein <ornstn@home.com>]

At 07:52 AM 26/06/01 -0400, philidor11 wrote:
> It's possible to disagree with each of the following statements:
> First, all animals with feathers are closely related.
> Second, if one or more of a group of closely related animals have feathers,
> then all other animals in the group had feathers.  (This assumes it is
> possible to determine conclusively that the animals are closely related by
> ancestry, using characters not limited to feathers.)

One difficulty with being too solidfirm on this point is that we really 
only know of a very few dinosaurs with definite feathers, as opposed to 
integumentary structures that might well be feather homologues but have not 
been conclusively proven to be so.  The structures in (say) Sinosauropteryx 
could just possibly be analogous to feathers rather than homologous with 
them (as are, I presume, the "hairs" of pterosaurs), in which case we 
really can say very little about the integument of all the animals in the 
clade containing both Sinosauropteryx and birds beyond noting a tendency 
within the group to evolve a hairlike or featherlike  covering.

Mind you, I think assuming that the Sinosauropteryx structures are feather 
homologues is a reasonable working hypothesis - but (unless I am much 
mistaken) it is, pending further evidence from microstructure, no more than 
that.


--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
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