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Re: TROODON, FABROSAURUS AND TOOTH TAXA IN GENERAL



In a message dated 97-09-09 08:30:17 EDT, smithjb@sas.upenn.edu (Joshua
Smith) writes:

<<      _Aublysodon_ teeth are not diagnostic?  Really?  OK, so where is 
 this published?  A), is there enough data for this hypothesis to be 
 considered valid and testable, and B), by which method have you tested it?>>

I published this notion in my articles on tyrannosaurid relationships for
Gakken. _Aublysodon_ teeth have been found in several different genera, so
they are not diagnostic to the generic level. >This< test is finished. They
are, however, (presumably) diagnostic of the subfamily Shanshanosaurinae, the
only subfamily in which they've so far been found. Showing something is
nondiagnostic is akin to falsifying a hypothesis, which can be done with a
single counterexample; showing something is diagnostic is akin to proving a
hypothesis true, which cannot be done except perhaps by the test of time.
Tomorrow someone may find _Aublysodon_-like teeth in genuine tyrannosaurines,
and "poof!" there goes the diagnostic value of those teeth at the subfamily
level.
 
<<      As far as your (George) hypothesis (I assume that you have 
 analized this enough to determine that it IS a testable hypothesis...) 
 concerning the lack of denticles on what you are calling lateral carinae 
 on the premaxillary teeth of _Aublysodon_, where do my cf. _Aublysodon_ 
 premaxillary teeth with denticulate carinae fit into this scheme.  How 
 many specimens have you used in your test of your hypothesis?>>

I've gone by the literature: about 20-30 references on _Aublysodon_.
_Aublysodon_-like premaxillary teeth _with_ denticles may belong to juvenile
tyrannosaurines. If you can show that denticles can exist on shanshanosaurine
premaxillary teeth, it would be a most valuable finding for the taxonomy of
tyrannosaurids. By increasing the number of genera in Tyrannosauridae that
may have _Aublysodon_-like teeth, you'll absolutely destroy that genus.
 
<<      Also, just to play Devil's Advocate, I would say to both Jeff and 
 George, just exactly what are you calling "diagnostic" about any of these 
 teeth and has this hypothesis been tested and by what method?  
 _Aublysodon_ sp. teeth are unusual, yes, but just what is diagnostic 
 about them?  Position and possession/lack/shape of denticles?  Is this 
 diagnostic for theropod dentition?  Can you prove it?  Before we can say 
 that teeth are not diagnostic or are diagnostic, work needs to be done 
 on what is or isn't diagnostic about them and why.  This is a rather 
 large project that has not been done yet for any dinosaur taxon.>>

I see you've gotten to the extreme end of the arc of the swinging pendulum
concerning what is or is not diagnostic with respect to dinosaur taxa. See
above.
  
<<      As for you point about it being inconceivable for a single 
 dinosaurian genus to produce such an abundance of teeth across such a 
 large paleogeographic (indeed geographic) area, why not (this is NOT to 
 say that I agree or dissagree with you, I am just saying that you have 
 dropped a rather large speculation out here, and do you have any evidence 
 to back up the claim)?>>

I know of no bona fide dinosaur genus that is found with such a wide range
and duration. (Entire Campanian and Maastrichtian; eastern Asia as well as
most of western North America.) In previous instances of such wide
paleobiogeographic ranges, such as with _Megalosaurus_, systematic revision
has subsequently shown the genera to be polytypic: several genera lumped into
one. Since _Aublysodon_ is based >entirely< on premaxillary teeth, it is
overwhelmingly likely that this has happened in this case.
 
<<      This falls very close to the nasty border of discussing exactly 
 what is a dinosaurian genus in the first place; something that would be 
 very interesting, but probably also very frustrating to discuss in this 
 forum.>>

Since dinosaur taxonomy above the level of individual specimens is entirely
subjective (cladistics notwithstanding: Nature doesn't care what we call
these things or how we arrive at our classifications), this would indeed be a
fruitless discussion. Like the perpetual argument between lumpers and
splitters.