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varmintman: "Mathematically, the point at which top lifters become dysfunctional because of that square/cube problem is around 20,000 lbs and the biggest elephants are around 14,000 - 15,000.
That's the present size limit for Earth.
That means that there has been a very large increase in gravity on our planet fairly recently, and it means that everything Einstein ever said about gravity is wrong..."

Rubbish, you should be ashamed of yourself.

The largest Sauropods are estimated upwards of 100 tons.
Recent models show that physical limitations on their size was neither bone nor muscle strength, but joints.

According to this site:

"In 2013, in a study published in Plos One on October 30, 2013 by Dr. Bill Sellers, Rudolfo Coria, Lee Margetts et al, Argentinosaurus was digitally reconstructed to test its locomotion for the first time.
The results of the biomechanics study revealed that Argentinosaurus was mechanically competent at a top speed of 2m/s (5 mph) given the great weight of the animal and the strain that its joints were capable of bearing.
The results further revealed that much larger terrestrial vertebrates might be possible, but would require significant body remodeling and possible sufficient behavioral change to prevent joint collapse."

And while we're at it, this big-fellow (Indricotherium, compared to an African elephant) weighed in around 20 tons, some 25 million years ago:

And this big-fellow (Songhua River Mammoth compared to African elephant) also grew nearly 20 tons, as recently as 10,000 years ago:

Thanks. I've replied to this one before, and you're right. It's baloney.

The obvious counterargument is, "You're RIGHT! that's why Blue Whales do not exist." Typically, you get back that they spend their time in the water, which of course, Sauropods did for large parts of their life cycle as well.

It aint easy being huge. But it's far from impossible.

Recent models show that physical limitations on their size was neither bone nor muscle strength, but joints.

A chain is no stronger than its weakest link. The fact that the limitation imposed by muscle dynamics is approximately 20,000 lbs means that any larger limit allowed by consideration of joints or anything else is irrelevant.

BroJoeK, it isn’t locomotion that is the problem, it is the cube square law and the increase in mass. The literal energy required to MOVE and support the MASS increases as the size increases but the efficiency of the muscle doesn’t. We know the efficiency of the chemical engine that drives muscles and if gravity is a constant one G, then because of the cube/square law, there is a point at which a living organism cannot support its own weight against gravity, much less move, eat, procreate, or support its internal organs with those muscles. This is easily calculated given the known limits of the theoretical strengths of tissues. 100 ton animals are simply not possible under one G.