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Homology and Clarifying Terminology



Won't write too much on this ... there's a world of difference in
application aside from definition. My operative use has been the
dictionary and I choose to apply terminology strictly, and I state my
premise of use like this at the beginning of most of the work that I
compose. This will become apparent in the near future should that paper be
published....

  Anyway, use of the term homology has been applied in such a way that,
even though considered not indicative of a common ancestry (though in
typological frameworks it was; and in early Linnaean constructs, as well),
the wings of bats and birds are homologous to one another. They are both
arm-assisted flying structures, with an internal brachial skeleton. This
too can be used for dipnoans and chondrostean fish, which employ the
pectoral anatomy in such a way. Thus, fish fins and birds' wings are
homologous. But the relation and degree must be elucidated.

  But as my friend Pete Buchholz says, there is a difference between
_functional_ and _synapomorphic_ homology. It's an indication of how they
are _used_, not through any exact meaning of the word. This is how words
can shift in meaning or application, and people may become entrenched in
the idea that a new or old form of a word may be the only form. So I
explicitly stated that my use was from a specific source. They may not be
clear, but they were not wrong, either, and the use of "homology" as to be
synonymous with "synapomorphy" is true, as well ... to some people. It is
not _the_ definition.

  Thus, in my most recent manuscript, I include two sections at the
beginning of the text to describe both nomenclature of taxa that will be
preferred and definitions favored for application to describing groups of
material, and terms for description of features in anatomy. This is also
why most recent works on anatomy on dinosaurs include a short statement
that terms for places of anatomy "follow Baumel and Witmer, 1993." It is a
statement of protocol for establishing reference of terminology. Quite
handy:

  "... and hence, use of the name Troodontidae will be in reference to a
clade of taxa that includes *Troodon*, and all taxa closer in ancestry to
*Troodon* than to *Ornithomimus* or Neornithes, and all descendants of
that ancestor..."

  This clarifies how the author uses "Troodontidae," and leaves no doubt
as to how some associated vernacular nomenclature, like troodontid, are used.

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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