RE: Definitions

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Steven Mahon
> Sent: Tuesday, August 05, 2003 2:14 PM
> To: dinosaur@usc.edu
> Subject: Definitions
>
>
> Hello All!
>
> I would like to know if there are any other
> definitions of the following: Dinosauria, Saurischia,
> Ornithischia, Theropoda & Sauropodomorpha. They dont
> have to be explicitly defined.

I don't know what you mean by "other" definitions, but here are the
phylogenetic definitions already published:

Dinosauria is _Triceratops_, Aves, their most recent common ancestor, and
all of its descendants (Padian and May, followed by Sereno 1997; however, a
second school holds a definition _Iguanodon_, _Megalosaurus_, their most
recent common ancestor, and all of its descendants).

Ornithischia is _Triceratops_ and everything closer to it than to Aves.
(Padian and May, uncontested).

Saurischia is Aves and everything closer to it than to Ornithischia
(Gauthier 1986; only modification are specific taxa for "Aves" and
"Ornithischia").

Theropoda is Aves (modern birds) and all taxa sharing a more recent common
ancestor with Aves than with Sauropodomorpha. (Gauthier 1986; other
formulations merely specify specific taxa within Aves and Sauropodomorpha).

Sauropodomorpha is _Cetiosaurus_ and everything closer to it than to Aves
(Padian et al. 1999) OR _Plateosaurus_, _Saltasaurus_, their most recent
common ancestor, and all of its descendants (Sereno).

Of all the above, only Sauropodomorpha has a really contentious pair of
definition: in one it is the sister taxon of Theropoda by definition, and
stem-based; in the other it is node-based and (based on the most recent
phylogenies) may excluded several "prosauropod-grade" taxa.

Hope this helps,

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796