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Re: The position of tyrannosaurs (was Re: Armour Symposium Recollections)



In a message dated 5/15/01 7:47:23 AM EST, tholtz@geol.umd.edu writes:

<< These are matters of generic synonymy rather than phylogenetic affinity:
 i.e., taste rather than position.  There still doesn't exist a
 "genericometer" or some other test to demonstrate when two species should be
 grouped in the same genus rather than split.  However, I and Currie and
 Brochu (at least) all use _Tarbosaurus_ now, and Chris and Thom Carr use
 _Albertosaurus_. >>

My own "genericometer" is something like this: Look at three-view drawings or 
photos of the two specimens being compared. If the differences between them 
are clear and obvious to the unaided eye, they can be considered to be in 
different genera (unless you suspect their differences are ontogenetic, which 
is a different ball game altogether). Once you start with the calipers and 
the statistical number-crunching, you're probably dealing with different 
species within the same genus at best.

If you look at drawings of Iguanodon atherfieldensis versus Iguanodon 
bernissartensis, they're quite easily distinguishable, so I'd place them in 
different genera (no less than three names may be available for I. 
atherfieldensis: Heterosaurus, Vectisaurus, and Sphenospondylus); certainly 
they're more distinguishable from each other in this manner than are any of 
the tyrannosaurids in the genera Albertosaurus, Gorgosaurus, and 
Daspletosaurus. If someone shows you a picture of a skeleton of 
Daspletosaurus, can you see right away that it's Daspletosaurus, or do you 
have to start counting teeth, eyeballing limb proportions, and so forth? Even 
the shape of the lacrimal horn varies enough that you don't know for sure 
whether you've got a Gorgosaurus or a Daspletosaurus.