Exposed teeth?

["Dino Rampage" <dino_rampage@hotmail.com>]

I?ve noticed something when people restore theropods; If the subject has its 
mouth closed, the artist tends to illustrate or sculpt it has having teeth 
that are exposed, like a crocodile?s. I?ve always found that although this 
gives them a more menacing look, I wonder whether it is practical at all. 
Has there been any evidence for lips that would have covered the teeth and 
hidden them from view in real life? Has anybody thought of the possible rate 
of water loss due to saliva evaporating from the exposed tooth surface? 
True, crocodiles do not have lips to cover the teeth, but considering that 
they live in a habitat where there is virtually no risk of dehydration, that 
is only obvious. How about dinosaurs, that were far more terrestrial than 
any crocodilian, and must have lived in far harsher and drier environments? 
Would it be more likely that they had lizard-like lips to minimise water 
loss? Most lizards have an impressive array of razor-sharp teeth, but for 
the most part they are hidden away when their owner has its mouth closed. 
Would dinosaurs have been similar in this respect? Or is it an archosaurian 
trait to have exposed teeth?

P.S I've seen most pictures of ornithischians with their teeth hidden by the 
cheeks and beaks, but as for sauropodomorphs, there are some pictures in 
which the upper teeth are exposed giving the sauropod a silly goofy grin. 
How accurate is it?

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