Was thinking about this today and am curious what you folks think.  Does the size of a planet determine the size of the lifeforms living there?  I know Earth has plenty of different sized creatures so maybe not.  But I have also seen documentaries on pygmy elephants that are small because their environment is smaller.  Maybe the average size would be larger or smaller.  I also think gravity would play a roll in it so maybe it would be opposite of what I was originally thinking as a larger planet would likely have higher gravity and thus smaller creatures.  What do you think?