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On the ovipary/vivipary of sea turtles, mosasaurs and other marine 
reptiles, here are some more ideas (following on from Dan Varner's 
words on the subject).

I reckon the fact that sea turtles never did get bigger that 
_Archelon_ and other giant protostegids is proof that they were 
constrained by ovipary. It may work like this: (1) embryo turtles 
derive calcium from the eggshell, (2) turtles cannot therefore 
dispense with eggshells, (3) turtles have to lay eggs because they 
cannot dispense with eggshells, (4) sea turtles, which have to lay 
eggs because they are turtles, have to lay eggs on land, (5) sea 
turtles, no matter how pelagic, must therefore always be tied to 
breeding on land, and (6) because they have to breed on land, sea 
turtles cannot grow so big that they willl become immobile when on 
land. The same _might_ go for marine crocs like metriorhynchids (my 
only reference for this - AFAIK he is only author who has really 
commented on it - is Tarsitano 1983). If any of this is true, it 
correlates well with body sizes because neither the biggest 
protostegids or the biggest metriorhynchids got to the sizes of the 
biggest ichthyosaurs and plesiosaurs. 

Dan said...

>  Embryos have now been found associated with mosasaurs so 
>  keep them off the beaches in your restorations. 

To my knowledge, Doug Henderson was the only one to ever commit 
this sin (and in a very recent painting too). I've been told my 
restored mosasaurs look like 'penguins on acid'... dammit, I just 
can't resist doing my marine reptiles patterned in black and white:)

"It looked like a penguin on acid" - R. Freeman, 1998.