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While I was writing up my paper for the Black Hills 100th T rex anniv volume 
I realized a point about T rex that may be misleading considerations of 
whether o rnot Nanotyrannus and the Burpee specimen are juveniles of the 

There simply was no other tyrannosaur that went such a dramatic change in 
form as it grew up as T rex. For starters it was the biggest so there was the 
greatest change in size related features. But it goes beyond that. T bataar 
became almost as large as T rex, but it was much less modified than the former 
(skull of even the enormous type not nearly as extremely broad, teeth not as 
stout, much less powerful bite etc). The reason was that only T rex was 
with adult elephant sized ceratopsids, as has been pretty much verified by the 
Triceratops with healed T rex skull and horn bite marks being described by 
Happ. Adult T rex were therefore the most specialized and stoutest of all 
tyrannosaurs, and had to go through the greatest alterations from juveniles 
lifestyles were probably fairly similar to those of other young tyrannosaurs, 
were radically different from the grown ups. Expecting young T rex to be 
fairly similar to the mature uberpredators may be misleading, instead it should 
expected that radical changes occurred as size and lifestyles were entirely 
transformed. Similar changes occur in some of the larger Varanus. In some the 
adults even develop blunt, crushing teeth (see J Vert Paleo 4: 96-107 1984).  

While on Varanus, a well established genus containing dozens of species on 
three continents (there are no indications it will be split up, if anything 
super-sized Megalania may be sunk into the genus, Amer Natural 146: 398-414 
shows far more variation in in detailed anatomy and gross form than the 
entire Tyrannosauridae, which have long been known to be a conservative, 
group. Check out a gorgosaur and a T rex skeleton in the same museum and note 
how little difference there really is. See how much more difference there is 
between the broad snouted ora and a slender nosed dwarf Varanus literally 
hundreds of times smaller. Makes one think. 

G Paul