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Re: Re: Removing segnosaurs from Theropoda



> From: head@lust.isem.smu.edu (Jason Head)
> > As for "Thecodontians", you don't have to be a
> > cladist (and/or strictly adhere to monophyletic groupings), to recognize
> > that "thecodont" has NEVER described an actual group of related taxa.  It
> > was a garbage can ( a la megalosaur), for poorly understood archosaurs, and
> > has since been abandoned.
>
>And, pray, what other name is available for stem-archosaurs?
>
Nonmonophyletic groups do not need to be named.

>At present I would divide subclass Archosauria into the following
>infraclasses:
>       Thecodontia
>       Crocodylomorpha
>       Dinosauria
>       Pterosauria
>
>Can you think of another name for the group Olshevsky and I are
>calling Thecodontia?

"Thecodontia" as commonly used is a doubly (or even triply)-paraphyletic term.
It includes the basal Archosauriforms (chasmotosaurs, erythrosuchids,
euparkeriids) and the basal pseudosuchians/crurotarsians, and the basal
ornithodirans (if you consider Marasuchus, Lagerpeton, and Schleromochlus
"thecodonts").

Under most archosaur workers phylogenies, the majority of the classical
"thecodonts" (rauisuchids, aetosaurs, parasuchians, etc.) are recognized as
sharing a more recent common ancestor with crocodiles than with the dinosaur
(bird) + pterosaur clade.  This group is called Pseudosuchia, or (for those
who'd prefer crocodiles not be among the "false crocs") Crurotarsi.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084