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Re: Dinosauria---Rejected Name?



philidor11 wrote:


> First, thanks for responding.
    No sweat. :)

> I'd also assume you wouldn't argue that every possible clade
> must be named;
    I am adamantly against this... I think excessive naming obviates the
utility of nomenclature in "minimizing cognitive effort" (a quote I
currently am unable to attribute, it's some psychologist Tim Rowe likes to
quote).

> As I read this, there are animals which HP Holtz decided were linked in a
> way important enough to be worth naming, and which was given the name
> Arctometatarsalia.
> (The 3 sets of animals he included must share a common ancestor, but not
all
> sets of animals are worth formulating a name for.  These were.)
    Ok, I should have explained further... the definition he used only
specifies a SINGLE included taxon, Ornithomimids. It was something like
"Ornithomimus and all taxa closer to it than to birds."

> Suppose that for some reason he had removed all 3 groups.  You would then
    Ornithomimus cannot be "removed," because it is included in the
definition. It is like type specimens/ taxa in traditional taxonomy... it is
one of the "anchors" to which the name is attached. This is true of any
phylogenetic definition (well, almost any), there is always at least one
member of the defined clade.

> We cannot point to that ancestor; a clade's existence does not rest on the
> ability to find a specific fossil to be the ancestor.  To the extent that
> primitive/derived characters are identified, an implicit description of
the
> ancestor is developed.  Because that description is the result of
inference,
> I used the term hypothetical.
> Because the group name, or entity name if you like, may be derived from
some
> attribute of the hypothetical (descriptively) ancestor, this becomes
> important.  The attribute which identifies the clade would be considered
> _essential_ to the clade, no?
    I think you are following the idea that a group of organisms *must* be
tied to particular characters. This is antithetical to the phylogenetic
nomenclature approach, which rejects essentialist, character-based
definitions. In its simplest form, we identify a clade (a common ancestor
and all of its descendants) by using a simple formula to point to the common
ancestor. The most basic example is, "the most recent common ancestor of
species A and species B and all of its descendants." This makes no
statements regarding the "characters" (if such things exist) of the species
included or excluded. May I suggest you go back and reread the early papers
on phylogenetic taxonomy (see ref.s below)?

> I would have expected that any group is named because of
> resemblances among the membership,
    Again, I think you may be missing the point of the post David quoted...
although it is common to refer to clades as "groups," a clade is an
individual, a real unit of genetic history. Effectively, where a group is a
plural, a clade is a singular. We can make whatever *groups* we want out of
the diversity nature provides, and name them whatever we want. However,
phylogenetic nomenclature approaches the issue from the other side: we know
a clade exists: give it a name, and see if a particular taxon is part of the
clade or not.

> You certainly set a high value on the unimpeachability of a construct.
    On the contrary, I recognize an impeachable reality, and eschew
construction. :)

    Wagner

Refs:

De Queiroz, K. and J. Gauthier. 1990. Phylogeny as the central principle in
taxonomy: phylogenetic definitions of taxon names. Systematic Zoology,
39(4):307-322.

De Queiroz, K. and J. Gauthier. 1992. Phylogenetic Taxonomy. Annual Review
of Ecology and Systematics, 23:449-480.

De Queiroz, K. and J. Gauthier. 1994. Toward a phylogenetic system of
biological nomenclature. Tree, 9(1):27-31.


Jonathan R. Wagner
9617 Great Hills Trail #1414
Austin, TX 78759