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Re: Cladistic definitions of Dinosauria, Saurischia, Sauropodomorpha




On Mon, 19 Sep 2005 12:25:19 -0700 "T. Michael Keesey" <keesey@gmail.com>
writes:
> On 9/19/05, Phil Bigelow <bigelowp@juno.com> wrote:

> > 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?


I never claimed it was.  But, provided that the specifier was already
widely known to be solidly within the clade (known from extensive
empirical evidence), then its "edginess" makes the definition all the
more sweet.


> 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.

IMO, cladistic definitions should recognize and embrace both change and
advancement in the science (provided that there is preexisting and
abundant empirical evidence to do so).  Ostrom's ground breaking
character trait work and Gauthier's early work on the cladistics of the
group should be formalized into the definition of Dinosauria, which in my
opinion only further compliments Owen's original name for the group. 
Both Owen and Padian and May win.  Tradition is preserved (to some
extent), and yet change is also recognized and respected.


> 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.


Congruency of an idea over time has its good points, no doubt about that.
 But should that be one of the prime factors in defining a clade? 
Shouldn't the communication of new knowledge also be a factor?

But by leaving birds out of the definition, we are only placating
Feduccia, Martin, Olsen, and a couple other hold-outs (some of whom show
ignorance of the available character data set).  The rest of the world
has moved on.

<sigh>Okay, how about a compromise definition:

Dinosauria = (Gallus gallus + Iguanodon)

eh?  eh?

<pb>
--