Re: Archosauromorph classification & Thecodonts

["Timothy Williams" <twilliams_alpha@hotmail.com>]

Ken Kinman wrote:

>      Actually I have been asking around for opinions on whether I should
> include choristoderes as well, and if so, should they be placed as (1)
> sister group to rhynchosaurs;  or (2) as sister group to rhynchosaurs plus
> all the rest of the thecodonts.

This came up recently:
http://www.cmnh.org/fun/dinosaur-archive/2000Jun/msg00136.html

> It's no
> different than Class Reptilia being all amniotes minus their mammal and 
> bird
> descendants, but being paraphyletic I guess you would call that a
> "trash-can" too.

Yep, I would regard "Reptilia" as a trash-can.  At least under the 
definition (as opposed to "diagnosis") under which birds (Aves) and mammals 
(Mammalia) are excluded because they are "warm-blooded".  Crocodiles are 
more closely related to birds than to turtles, yet the crocs are lumped in 
with the turtles.  Mammals get their own class, yet pelycosaurs have to stay 
behind in the Reptilia because they weren't clever enough to evolve an 
endothermic metabolism.  Etc.


>     But as far as "trash-cans" go, Dinosauria and a lot of other groups
> have had problematic groups thrown into them which were later removed.

Yes, but the difference is that the "Thecodontia" seems to be specifically 
designed to *accommodate* problematic taxa.  Any archosaur that wasn't a 
dinosaur/crocodilian/pterosaur was stuck in the Thecodontia.  Non-dinosaurs 
are occasionally assigned to the Saurischia and Ornithischia, but these are 
removed when their true affinities are realised.  With thecodonts like 
_Lagosuchus_ and _Sphenosuchus_, you seem intent on keeping them among the 
thecodonts *despite* the fact that their closest relatives have been 
identified (and they're *not* thecodonts).


Tim
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