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Lagosuchus is a valid genus (was Re: Lewisuchus, a Dinosauriform)


Mike Keesey wrote:

--Dinosauromorpha
  |--Lagerpeton
  `--Dinosauriformes
     |  ?Lagosuchus [nomen dubium]
     |--Marasuchus
     `--+--Pseudolagosuchus
        `--Dinosauria



I do believe that _Lagosuchus_ is a valid genus.  Sereno's observation that
the type specimen lacks autapomorphies is not (IMHO) a reason for
disqualifying _Lagosuchus_ as a valid taxon.  _Lagosuchus_ can be
distinguished from other basal dinosauriforms (including _Marasuchus_), all
of which have apomorphies that are clearly absent from _Lagosuchus_. That in
itself is a diagnosis.  In fact, the absence of autapomorphies is exactly
what we would expect in an ancestral taxon like _Lagosuchus_.


Tim

------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163



From: "T. Mike Keesey" <tmk@dinosauricon.com>
Reply-To: tmk@dinosauricon.com
To: Christopher Pearsoll <c_pearsoll@hotmail.com>
CC: <dinosaur@usc.edu>
Subject: Re: Lewisuchus, a Dinosauriform
Date: Mon, 23 Jul 2001 14:01:01 -0400 (EDT)

On Mon, 23 Jul 2001, Christopher Pearsoll wrote:

> So what order are the 'Lagosuchians' in and where do they fall within (
> or out ) of clade dinosauria?

Some of us prefer to eschew "orders" and other such arbitrary ranks.
"Lagosuchians" (a paraphyletic group) are in _Dinosauromorpha_, but not in
_Dinosauria_ (and all, except probably _Lagerpeton_, are in
_Dinosauriformes_).

--Dinosauromorpha
  |--Lagerpeton
  `--Dinosauriformes
     |  ?Lagosuchus [nomen dubium]
     |--Marasuchus
     `--+--Pseudolagosuchus
        `--Dinosauria

Is, I think, commonly accepted. (Some would place _Eoraptor_ and
_Herrerasauridae_ closer to _Dinosauria_ than _Pseudolagosuchus_ is --
others place them within _Dinosauria_.)
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