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Re: Ceratosauria vs. Neotheropoda?



On Mon, Nov 23, 2009 at 3:16 AM, Mike Taylor <mike@indexdata.com> wrote:
>
> In what sense is the clade Theropoda "comparable" with the clade Apatosaurinae

They're both founded by a single population and include all
descendants thereof? Seriously, why *not* compare them, as long as
you're comparing all relevant, disjoint clades to each other? It
depends on the context.

> This is a complete non-sequitur. ÂFormally defining a paraphyletic
> Prosauropoda would not in any sense "get in the way of" the clades
> Sauropodomorpha and Sauropoda.

FWIW, it would get in the way of Sauropodiformes, at least in a ranked
system: http://www.taxonsearch.org/dev/taxon_edit.php?tax_id=768&Action=View

You're right, though that you could have a system where taxa are
allowed to overlap. The PhyloCode, for example, allows overlap between
clades in cases of hybridization, endogenous symbiosis, etc.

However, nobody has really formalized such a system for grades. If
you're serious about it, why not follow in the footsteps of
phylogenetic nomenclature?

1) In your papers, wherever you want to use names for grades, define
them up front. (Gregory Paul did this in Dinosaurs of the Air, for
example.) Allow them to overlap.
2) If this is something useful, you'll be able to convince more and
more people to get on board with it.
3) Once there's enough momentum, start to look into codifying the practice.

I still think, though, that formal names for grades would have to
follow some other kind of orthographic practice. (Asterisks won't
work, for reasons David Marjanovic listed.) Perhaps lower-case? That
way, when you discuss prosauropoda and Sauropoda, it's apparent that
they are different types of entity.

Or, Paul used hyphenated prefixes as shorthand, e.g., "dino-" for
"non-avialan". This is somewhat similar to the practice of using
"stem-" for stem groups (a specific type of grade). Currently the best
way to refer to most paraphyletic groups is by formulaic phrases like
"non-colobine primate"*, "non-apo-testudine apo-tetrapod"**, etc. So
one solution could be to find ways of abbreviating those formulae.***

* The grade of primates with thumbs.
** The grade of limbed vertebrates with pectoral and pelvic girdles
outside of their ribcages.
*** This list of footnotes is starting to look rather Borgesian.

-- 
T. Michael Keesey
Technical Consultant and Developer, Internet Technologies
Glendale, California
http://tmkeesey.net/