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Mammalian teeth (was CRETACEOUS VARANIDS)



Sean Connell wrote:
> 
> Toby White wrote:
> >
> > Darren Naish said:
> >
> > >got virtually no mammalian carnivores). This theory, nice as it is,
> > >has been invalidated by the large number of Australian marsupial
> > >carnivores described in recent years: new dasyuromorphs, carnivorous
> > >macropodids and thylacoleonids a-plenty.
> >
> > I get the impression that mammals change dietary habit quite easily, whereas
> > dinosaurs (AFAIK) have made the transition only twice, both times from
> > carnivore to herbivore (unless one includes birds).   Furthermore, I've
> > never heard of a dinosaurian omnivore.  Perhaps they exist, but it doesn't
> > seem to have been a common habit.  Is there a simple explanation for this
> > pattern?
> >
> >   --Toby White
> Mammals have an advantage in this by virtue of tooth design.Mammals have
> a variety of tooth shape in their mouths...molars (for grinding),
> canines(for puncturing), etc..This makes it a bit easier to move from
> one end of the diet spectrum to another if they feel the evolutionary
> "push" :)

Mammal teeth also seem to be better able to "improvise" than those
of most dinosauria. Thylacaleo is a good example. It was actually
decended from herbivores and so lacked canines or carnassials. The
solution? Turn the two prominant front incisors in both the upper
and lower jaw into sharp canine-like teeth, and to fuse most (all?)
of the cheek teeth into one continuous blade. The resulting skull
looks typically carnivorous at first glance, until you notice that
the "canines" are completely in the wrong place. I don't know
of any dinosaur species that managed such a feat of dental
improvisation.
-- 
____________________________________________________
        Dann Pigdon
        Melbourne, Australia

        Dinosaur Reconstructions:
        http://www.geocities.com/capecanaveral/4459/
        Australian Dinosaurs:
        http://www.alphalink.com.au/~dannj
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