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homologies in context (epidermal structures)




Tom,
I think you might find that your owl intermediates are scutes (or scutellae) rather than scales. And although there is probably some degree of homology to scales, it appears that feathers and scutes are much more closely related.
There is a sort of hierarchy of homologies, and teeth in particular are so remotely homologous that it is irrelevant to what we are discussing here. If we were on
an invertebrate list, I would have yesterday brought up the possible homologies between polychaete external structures (which you mentioned) and internal structures such as the mollusc radula and bryozoan gizzard teeth. Interesting, but not relevant to scales, scutes, or feathers.
Go back far enough, all life is homologous since all our cells and organelles are just modified bacteria. So homology has to be taken in context to be of value. Fish scales can be pointy too, but that doesn't mean they have anything to do with scutes or feathers.
-----Cheers, Ken
*******************************************
From: TomHopp@aol.com
Reply-To: TomHopp@aol.com
To: dinosaur@usc.edu
Subject: Re: epidermal structures.
Date: Mon, 27 Aug 2001 13:38:39 EDT

Alan Brush wrote:
<<we have become sloppy with some important definitions>>
Sorry Alan, I was just trying to emphasize the possible commonality of many
pelage-like things. Fortunately for us all, I'm probably the only one (at
present) who thinks feathers and teeth have anything in common.

<< One significant difference between feathers and scales is that feathers
are tubular and scales are planer. The surfaces are probably not homologous.
There is no evidence that scales are transformed into feathers or that
feathers are transformed into scales. >>
Though I know your ornithological knowledge is extensive, I think you may
have missed a detail. I recall having seen photographs of bird scales that
have feathery tips. I don't recall which species, but I think it may have
been an arctic owl. Given such half-scale half-feather entities, it becomes
obvious that somehow the two must share a common ancestral structure, and the
tubular and planar structures are interconvertable. These days, I'm starting
to suspect the tubular, pointy structure came first, then flattened later to
yield scales. Why not?



Thomas P. Hopp Author of DINOSAUR WARS, a science fiction novel published by iUniverse Now Humans are the Endangered Species! http://members.aol.com/dinosaurwar

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