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Tooth Counts in Tyrannosaurs



Berislav Krzic wrote:
> 
> Nevertheless, [1] I think the tooth count is wrong for T. rex (N.
> >lancensis has too many teeth and so might be a different species of
> >Tyrannosaurus), and [2] those dramatic skull growth changes better not be
> >>too< dramatic, lest we mistake real phyletic differences for ontogenetic
> >changes (how many growth specimens of T. rex, with skulls, do we have,
> >anyway?). Should be an interesting study either way.
> >

        Hold on here. I will probably have to envoke Holtz's Law here and say 
wait for the Smith and Lamanna (in press) paper on utility of theropod 
teeth as systematic characters to come out, but I will say this:  
_Nannotyrannus_ and _T. rex_ both have the same premaxillary tooth count 
at 4.  Premaxillary tooth count does not vary among theropod taxa (unless 
you count what Phil Currie said at the Ostrom symposium about Sino (still 
looking into the validity and implications of this statement) and 
unless you count _Dilophosaurus sinensis_ (but there I would refer to the 
Lamanna, Smith, Holtz et al. 1998 JVP abstract and our concerns about the 
validity of _D. sinensis_ on other grounds...)).  It thus MIGHT be a good 
systematic character (I will let you know my thoughts on that in about 
two weeks when the rest of the analyses are finished...). 

 HOWEVER, concerning maxillary and mandibular tooth counts:  we have 
finished the work on this and these are BAD BAD BAD characters.  In every 
single instance where we have enough specimens of a taxon to come close to 
statistical significance (bloody few taxa...), maxillary tooth count is 
variable and mandibular tooth count is HIGHLY variable WITHIN species.

        _Herrerasaurus_ maxillae have between 17-18 teeth, even for the 
pathetically few maxillae known.

        _Torvosaurus_ has 10-13 teeth in the one examined specimen.

        _Coelophysis_ has 22-26 maxillary and 26-30 mandibular teeth.

        _Tyrannosaurus rex_ has between 11-13 maxillary and 13-14 
mandibular teeth.

        _Albertosaurus cf. sarcophagus_ has been 13-15 and 14-18.


        Just because CMNH 5741 preserves 15 maxillary alveoli (the 
mandibular count is speculative as we all know), the data indicate that 
this says nothing about the taxonomic validity of _N. lancensis_.
        Maxillary and Mandibular tooth counts: bad characters, bad bad
 characters.


        Incidentally, to stir the waters a bit, the morphological 
variation in _N. lancensis_ and _T. rex_ maxillary dentition is not 
really that similar...but wait for the papers.

        



-- 
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Josh Smith
University of Pennsylvania
Department of Earth and Environmental Science
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