[masklinn]

Sauropods were light for their size, the air sacs definitely did a lot of work, though so did much of the size being neck and tail.

Argentinosaurus is estimated to have reached 35 metres and 80 tonnes at the upper range, for comparison blue whales top out at 30 meters and 200 tonnes.

You can see something similar with giraffes, though without the benefit of tail (or air sacs). Male giraffes average above 5m tall (tallest known was 5.8m — 19ft) compared to a bush elephant's 3.2 (4 at the absolute limit), but the average male giraffe is just 1200kg versus 6000 for elephants.

Obviously Sauropods were still bonkers heavy, to a ridiculous degree for land animals.