Re: The Biggest Dinosaurs

[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.