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Re: Cladistic definitions of Dinosauria, Saurischia, Sauropodomorpha

On 9/19/05, Phil Bigelow <bigelowp@juno.com> wrote:
> The Draft Committee is comparing apples and oranges when they speak of
> both Owen's 1842 name and the later cladistic definitions, and their
> opinion appears somewhat petty.

How is comparing a taxon named "Dinosauria" to a taxon named
"Dinosauria" like comparing apples and oranges?

> I *do* understand their reasons (they
> are trying to prevent "activist clade naming", where someone defines a
> clade in order to make a point _a priori_).  But I think the Committee
> should have used a different example to make their point.  John Ostrom
> and later,  J. Gauthier, solidified the position of birds as dinosaurs
> years before Padian and May's definition appeared in print.

That doesn't mean that "birds" is a good choice for internal
specifier. The positions of ornithischians, sauropodomorphs,
coelophysoids, ceratosauroids, spinosauroids, carnosaurs,
tyrannosauroids, ornithomimosaurs, oviraptorosaurs, therizinosaurs,
deinonychosaurs, etc. have also been solidified as dinosaurian, and
for far longer than that of "birds". (Jury still out on the positions
of herrerasaurids, "silesaurids", etc.)

> I like Padian and May's (1993) definition, not just because it appears to
> have date priority(?) over all other clade definitions, but also because
> it is "edgy" and current.

Since when is "edginess" a good criterion for specifier selection?

Yes, _Dinosauria_ has changed a lot since Owen named it. Many
characters in his diagnosis have turned out to be convergences, etc.,
and the number of species has gone from 3 to over 10,000. But the
three taxa he assigned to _Dinosauria_ have remained members of
_Dinosauria_ in *every single publication since* (excepting those
which deny _Dinosauria_ as a valid taxon). Unfailingly since its
inception, they have been part of _Dinosauria_. To me that's a far
better criterion.

And when you also consider that using the original members as
specifiers for a node-based clade creates a group which is congruent
with every single researcher's concept of "Dinosauria", well, it seems
like a done deal. Going back to the original usage doesn't work for
every taxon (_Reptilia_ would become _Gnathostomata_, _Homo_ would
include chimpanzees, etc.), but when it does, why not refer to it?

—Mike Keesey