You were arguing that gravitation in the Earth has some how increased in recent eons making it impossible for creatures much larger that elephants to have survived...I don’t know how much I agree with the plausibility of your opinion but I was just trying to reason it out. We have water creatures much larger than elephants, so I was just playing around with your opinions. I was trying to give you the benefit of the doubt.
Water buoyancy does in fact allow whales to attain sizes greater than land animals could survive at today but that had nothing to do with how sauropods lived. Sauropods required an outright reduction in gravity itself. That means that gravity itself is not a basic force in nature or any sort of a four dimensional differential geometry thing as Einstein claimed; it is basically some sort of an electrostatic dipole effect.