Denticle Size, was Re: Deinonychus

[Jaime Headden <qi_leong@hotmail.com>]

In the new paper, Denver Fowler and colleagues 
(http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0007999) 
write:

  "The teeth of troodontids are similar to those of dromaeosaurids in that 
denticles are reduced or absent on the anterior carina, with large hooked 
denticles on the posterior carina [66], [67]. Troodontid denticles appear 
proportionally much larger than those of dromaeosaurids, and compared to the 
crown height this is true. However, troodontids possessed many more teeth in 
their jaws than would have a similarly sized dromaeosaurid [67]. For a given 
fixed jaw length, troodontid teeth are comparatively much reduced in size; the 
crown height of troodontid teeth would have been only about half as much as 
those of a dromaeosaurid. Therefore it is probably more accurate to say that 
troodontids do not have large denticles; rather, they have short crowns, with 
similarly sized denticles as might be expected for a dromaeosaurid of similar 
body mass. This makes sense if denticles have a size below which they are no 
longer able to function effectively."

Tom Holtz writes in response to this:

<So, a test of this:
Measure denticle size in troodontid teeth (and dromaeosaurid teeth, and a 
couple other basal groups for comparison) AND the length of the tooth row of 
the same individual. Plot the two against each other.

If the Fowler et al. hypothesis is correct, the troodontid and dromaeosaurid 
data will plot with each other. Alternatively, it may be that the the enlarged 
denticle size in Troodon et al. will continue to scale above that of 
dromaeosaurids even when plotted against tooth row length rather than a measure 
of tooth size.>

  I hinted at my desire to do this test, but lack the means. However, I wonder 
if it is even necessary, or tell us much (of course, that doesn't mean we can't 
do it anyway, in case it does provide information). The reasoning is that in 
predatory teeth, serrations on an edge function as regions of high pressure, 
where tissues are gathering during jaw action (orthally or otherwise) and are 
concentrated. This is produced due to the gaps between denticles, called 
diaphyses. Tissues caught in these regions can, when led into a cella, be 
bunched and not cut. Otherwise, a wider gap with a cella simply cuts (as in 
carnassial cusps). The functional utility of the serrations should be either 
concentration of pressure between them, or distributing compressive forces 
along the margin of the carina. But serrations are an imperfect method of 
distributing forces; a smooth edge should function better for this purpose, 
regardless of curvature, and indeed in knives and other bladed tools, the edge 
of the blade concentrates forces to a single point, a "sweet spot" for slicing, 
which is usually around 3/4 the length of the blade from the base. So the 
functional purpose of the denticles may not have anything to do with their 
shape, but rather the gaps between them and their comparative morphology 
(presence of inter-diaphyseal keels, width and depth of the diaphysis, presence 
of a cella, etc.). Larger gaps mean more tissues can be gathered, while smaller 
gaps mean fewer tissues, or conversely fewer large tissues/many smaller 
tissues. Assessing the sizes of the gaps may be thus more functionally useful 
than the sizes of the denticles (then again, people seldom discussion the 
spaces between teeth and their functional analogues, although it's been done in 
mammals and crocs).

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
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