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Re: The Biggest Dinosaurs

> From:          John Bois <jbois@umd5.umd.edu>

> On 20 Aug 1997, Norton, Patrick wrote:
> > ...does anyone have any thoughts about why the upper absolute   
> > size of dinosaurs was so much greater than the upper absolute size of   
> > terrestrial animals today?  
> I believe it is because they guarded eggs.  A premium is put on defence
> rather than running.  In mammals it's the other way ariound and,
> apparently, pregnacy incurs not much of an increase in predation.
> Bolstering this claim is a finding in M de Fraipont et al, _The evolution
> of oviparity and viviparity in lizards and snakes: a phylogenetic
> analysis_, in Evolution 50(1) pp. 391-400."Our results show that
> egg-guarding is associated with an increase in size...(and)...viviparity
> is associated with a reduction in size..."  This is for snakes and lizards
> but one would expect similar forces to be in operation, i.e., it is easier
> to defend a nest when you are big.
That's an interesting point, John.  I wonder if there were other 
reasons as well, such as predator size increasing prey size 
increasing predator size unrelated to egg defense.  Or did it perhaps 
start there and escalate?  Or both?  Are they different or the same 
mechanism (assuming they occur)?  There's no doubt that prey and 
predator exist in everchanging equilibrium today.  Of course, there 
are other reasons for increasing size in animals.  Prey also have to 
compete with each other and plants, weather, etc.  Predators have to 
compete with each other, too.  Complicated.