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When does "live birth" become a critical survival edge?



Thomas and the Dinosaur Crew? :

As a layperson, I find these questions fascinating. The fast furry
reptiles
that went on to sweat and milk and live birth aren't the same type of
reptiles
that evolved into the theropod-like dinosaurs and birds. So what factors
would
cause those needs. Aren't the hearts of mammals four chambered and birds
three
chambered? 

I am curious as to when it becomes a bonus to invest time and energy in
rearing
offspring as well.

> You may want to have a look at the mammary system in monotremes and see how
> they differ from marsupials and placentals.  Although monotremes (echidnas
> and platypi) have their own specializations, they also retain many primitive
> features lost or transformed in other mammals.


- Alan ( visit www.nichimen.com )

PS  I meant no slight to Mark "Crash" McCreery nor to Stan Winston. I
offered
    the data to show that originally our scary movie monsters were sized
more
    correctly...