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     > ON THE PRESSURE EXERTED ONTO FORELIMBS when a rearing sauropod moved 
     back to it s
     > quadrupedal state, I feel it unlikely that much exertion of the 
     forelimbs would
     > have been needed. To rear into a bi/tripodal stance, a big dinosaur 
     > probably not need to 'push off the ground' with its forelimbs. 
     Simply leaning > back would tilt the sacrum, the counterbalancing of 
     the tail immediately liftin g
     > the thorax and neck. Lizards that rear in threat displays 'push up' 
     with the > arms, but their tails aren't far enough off the ground to 
     provide a levering > effect for the upper body. 
     =How does it "lean back" without using its forelimbs?  It seems to me 
     =like to only way to shift the animals balance backward would be to 
     =push off with the forelimbs.  If it isn't using these, exactly what 
     =is it flexing or tilting or whatever to shift the center of gravity?
     elephants (to use a sample that is viewable today) first bend their 
     knees (yes, on the back legs), then sit back on their haunches, and 
     then lift their front legs off the ground to rear up.  The lack of a 
     push-back by the front legs is probably because the front legs are 
     pretty straight and wouldn't give much vertical lift if flexed.