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tooth question



Some time back I was asking this same question of how to tell T.rex
teeth from Albertosaurus or other tyrannosaurid teeth.  I consulted the
same sources you did and asked around.  What I heard was that
Tyrannosaurus rex teeth are fatter and have larger, wider serrations. 
Well, how fat are they?  How many serrations per mm?  The only good
information on these specifics came from what I gleaned from the
following ref:

Farlow, J.O., Brinkman, D.L., Abler, W.L., and Currie, P.J. (1991). 
Size,shape and serration density of theropod dinosaur lateral teeth. 
Mod.Geol. 16, 161-198.

This article includes measurements taken from therapod teeth, including
28 T.rex teeth.  Importantly, the data on the T.rex teeth comes mostly
from in situ teeth of two specimens.  Unfortunately, the number of
Albertosaurus and other theraopod teeth measured was much fewer.

Though an answer to the above questions is not specifically given in the
above article, there are several graphs that I found revealing.  On the
question of fatness, the graph on p.165 plots tooth basal width vs.
tooth fore-aft basal length, or fatness.  Picking the coordinates of the
T.rex teeth out of the graph shows the T.rex teeth to have a surprising
range of fatness.  I found the tooth basal width:tooth basal length to
range from 0.5 to 1.0!  The mean and the average were 0.71.  While the
mean and average are not surprising to me, the range, particularly the
presence of relatively skinny teeth was.  Three of the sample of 28
T.rex teeth were less than 0.6, which is less than the basal width to
length ratio of the single Carcharodontosaurus tooth in the graph. 
Though the general trend is for T.rex teeth to be fatter as they get
longer, this is not always the case either.

Graphs on serration sensity are also revealing.  Across the board, the
larger the tooth, the larger the serrations.  So, though the T.rex teeth
appeared to have the least dense (larger) serrations, they were also the
larger teeth.  The T.rex teeth appeared to vary from about 6 serrations
per 5mm of posterior keel up to about 13 serrations per 5mm.  The single
Albertosaurus tooth had 13 serrations per 5mm.  A chart on p. 176
indicates a serration density 10-12 for Albertosaurus. 

What I conclude from the data in this article is that the best way to
definitely tell a T.rex tooth from that of another large therapod,
assuming you don't know what formation it is from, is to see what kind
of skull it is attached to.  There appears to be a wider variation in
T.rex tooth fatness and serration density than is commonly
acknowledged.  

Bruce Danz