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Re: Mongolian dinosaur inspires religion in grad student



Jonathan Wagner wrote:

>>Bullatosauria is the node-based taxon joining Troodon (or Stenonychosaurus,
>>as soon as a second distinct troodontid with the same tooth form is found in
>>the Judith River... :-() and Ornithomimus.

>        Uh, were you joking about the stenonychosaur?  I don't read smiley
>well...

No, it was a frown.  Unfortunately, within Mongolian formations, there are
often more than one distinct skeletal taxa of troodontid present.  This may
be the case in the Judith River.  Should we find two distinct troodontid
genera within the Judith River, both with tooth forms identical to Leidy's
Troodon, then we can no longer confidentally synonymize "Troodon formosus"
(a tooth taxon) and "Stenonychosaurus inequalis" (a skeletal taxon).  This
would produce a situation similar to what happened to Leidy's Deinodon: two
sympatric tyrannosaurid taxa with the same tooth form, neither of which can
be confidentally synonymized with Deinodon.

No one has reported a second Judith River troodontid yet, but I would not be
surprised one bit.

If that does happen, the name "Troodon" in the definition of "Bullatosauria"
will be replaced by "Stenonychosaurus" (which is why I made sure to include
a parenthetical note in the short 1996 paper).

>>>        I am still unclear on how to handle the apparent "synonomy" of a
>>>stem-based clade and a node-based clade...
>>
>>These will not be synonyms unless they use the same name.
>        Sorry, I cannot remember the terms...  I was thinking of... is it
>_subjective synonyms_ that include the same taxa?  Anyway, thanks for the
>clarification!

Two taxa under phylogenetic taxonomy will be subjective synonyms if they
wind up describing exactly the same node or stem, but with different
definitions (for example, Ceratosauria and Carnosauria would be subjective
synonyms if Currie's hypothesis, that Ceratosaurus is more closely related
to Allosaurus than to birds, proves true).  Two taxa are objective synonyms
if they have the same definition (for example, Gauthier's Tetanurae and
Novas' Avipoda, both defined as all taxa sharing a more recent common
ancestor with birds than with Ceratosaurus).

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"  :-)