Re: Serration variation

[Phil Bigelow <bigelowp@juno.com>]

On Thu, 10 Feb 2000 13:45:33 EST Dinogeorge@aol.com writes:

>Basal archosaurs were small reptiles with teeth too small to develop 
>serrations; their teeth themselves are the size of serrations on teeth 
>of 
>large theropods.


How small is "too small"?  I have seen serrations on 3 mm-long teeth
(base to apex of crown) from a fossil ?lamnoid shark (presently
unidentified as to genus/species).



>Appearance of tooth serrations in various archosaur 
>groups 
>is more likely size-related and independent (convergent), not due to 
>common 
>ancestry.


Convergence can certainly be a factor.
In living sharks, occurrence/absence of serrations is linked to how/what
the shark eats. Teeth from fish-eating sharks often lack serrations. But
scavengers/hunters of large mammalian prey usually have serrated teeth. 
The size of the shark doesn't seem to correlate that well with
presence/absence of serrations (this lack of correlation is also observed
in fossil taxa).

And I am not suggesting that ontogeny doesn't play some roll in serration
expression.  It is doubtful that the precocial babies/juveniles of 
troodontids ate mammals or lizards.  They probably ate things the size of
insects.  Serrated teeth are overkill for this type of feeding style (and
guess what....babies of at least one troodontid species lacked serrated
teeth).  My guess is that, with their coarsely-serrated teeth,  adult
troodontids were accomplished LARGE-animal scavengers, as well as being
good "mousers". 
Just my 2 pesos.


                                    <pb>





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