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RE: Greg Paul's new (or newly named) iguanodonts



> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of Tim Williams
>
> For example, the paraphyletic group "Thecodontia" might be 
> revived in discussions on bird origins, especially by the 
> tiny minority who advocate a non-dinosaurian origin of birds 
> (and who, as it is, tend to play fast and loose with 
> phylogenetic concepts).  We could see a paper containing 
> sentences like "Birds (Aves) probably evolved from 
> Thecodontia, given that primitive birds share the following 
> characters with thecodonts..."  Naming paraphyletic groups, 
> no matter how practical-minded and honorable the motive 
> behind it, could further confuse the distinction between 
> derived/apomorphic and primitive/plesiomorphic characters.  I 
> think the current practice of using (admittedly cumbersome) 
> terms such as "thecodont-grade archosauromorph" or 
> "non-dinosaurian archosauromorph" helps ensure that groups 
> like "Thecodontia" continue to be *excluded* from 
> phylogenetic discussions.  

As an old-timer who remembers when thecodonts were thecodonts for their OWN
sake (i.e., the group of basal archosauriforms of the Triassic), and not
part of the discussion of bird origins as such, I still think this is a
horrible idea.

The original work of Gauthier, Clark & Benton, Parrish, & colleagues back in
the 1980s was really to sort out this mess, and resolve that classic
archosaurs fell into three clusters: dinosaurs, pterosaurs, and their kin;
primitive guys (the traditional "proterosuchians" as well as Euparkeria and
Proterochampsidae); and the croc-ankle cluster.

And really: those who have argued for a "thecodont" origin since the 1970s
(Tarsitano, Martin, etc.) argued for relationships with animals that
thecodont workers (Charig, Parrish, Chatterjee) would not consider
thecodonts at all!! (This is opposed to the Heilmann model, which did derive
birds out of Euparkeria-like forms).

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Fax: 301-405-0796

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA