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Re: Formal definition of the Dinosauria



Jeff Poling wrote:

>   While arguing with the author of Ask Shagg over the proper definition 
>of a dinosaur (the guy used an english dictionary, rather than a natural 
>history text) I realized my article called "Dinosauria defined" does NOT 
>have the definition of dinosauria.  It has Gauthier's 1986 definition of 
>Saurischia and Padian's 1993 definition of Ornithischia, but not a 
>similar definition for Dinosauria.
>
>   So whut is the "official" definition of dinosauria?

The definition of Dinosauria is something you can get into public debates
over... :-)

Under phylogenetic taxonomy, Dinosauria = all descendants of the most recent
common ancestor of _Triceratops_ and modern birds (Holtz & Padian, 1995, and
in prep.), with Ornithischia = all taxa sharing a more recent common ancestor
with _Triceratops_ than with Saurischia (Padian & May, 1993) and Saurischia =
all taxa sharing a more recent common ancestor with birds than with
Ornithischia (Gauthier, 1986).

When I suggested how much nicer things would have been if they had used
_Iguanodon_ instead of _Triceratops_ and _Megalosaurus_ instead of modern
birds, they thought it was a great idea.  Unfortunately, under the
principles of phylogenetic taxonomy, the first definition of a taxon under
those rules has priority.  Oh, well.

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

"There are some who call me...  Tim."
-- Tim the Enchanter, "Monty Python and Quest for the Holy Grail"

"Tim?!?  They called me TIM?!?!"
-- me, on seeing the credits to "The Ultimate Guide to T. rex"  :-)