tyrannosaur tooth diversity

[Farlow@IPFW.EDU (Farlow,James)]

     Commenting on George's mini-monograph about tyrannosaurid systematics, 
     many years ago I did a big project on the functional morphology of 
     theropod teeth, ultimately published in 1991 in _Modern Geology_.  I 
     was particularly interested in tyrannosaurid teeth from what is now 
     called the Dinosaur Park Formation.  I looked at _in situ_ teeth in 
     the jaws of what was then called _Albertosaurus libratus_, but seems 
     now to be headed back to _Gorgosaurus libratus_, and also at _in situ_ 
     teeth of _Daspletosaurus torosus_.  I noticed some dental features 
     that were consistently different in the two forms:
     
     1)  Shape of the anterior serration keel: As you follow the anterior 
     keel from the tip of the tooth toward its base, in _Gorgosaurus_ the 
     keel curves sharply medially, toward the inside corner of the tooth.  
     In _Daspletosaurus_ the medial bending isn't anywhere near as 
     pronounced.
     
     2)  "Crinkles" along the posterior serration keel:  In 
     _Daspletosaurus_ teeth, but not _Gorgosaurus_ teeth, there are little 
     crescent-moon shaped crinkles that run a short distance from the 
     posterior serration keel onto the side of the tooth.
     
     In all the jaws of _G_ and _D_ that I was able to examine, and that 
     had been assigned to genus on the basis of non-dental criteria, the 
     difference between the two tooth morphs held up.  I haven't worked on 
     theropod teeth in a decade now, so I don't know if they still hold up, 
     but I mention them for whatever they may be worth.
     
     Now, this has no bearing on the question of whether _G_ and _D_ belong 
     to the same genus or different genera, but it does suggest that they 
     really are distinct at the species level.
     
     Jim Farlow