They were the biggest land animals ever, but how did sauropod dinosaurs get so huge? (Image: Christian Darkin / SPL)

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BEFORE my visit to Argentina, I had no real grasp of how large the very biggest dinosaurs could be. In the end, all it took was a glance at a single bone.

I was in the Argentine Museum of Natural Sciences in Buenos Aires when I came across a vertebra from a dinosaur’s back. What to compare it with? A human vertebra would fit comfortably in the palm of your hand. An elephant’s would take two hands. At 1.6 metres tall, the vertebra in front of me was on another scale entirely – it would need a forklift truck to shift it.

The vertebra belonged to argentinosaurus, a 100-million-year-old dinosaur that, as far as we know, was the biggest land animal that ever lived. In life it was 35 metres long and weighed around 80 tonnes.

Argentinosaurus is a member of the sauropods, an instantly recognisable group that includes diplodocus, brachiosaurus and apatosaurus. Sauropods had long necks, long tails, barrel-shaped torsos and trunk-like legs. They weren’t all enormous, but the big ones were extraordinary.

No land animal has come close to the size of argentinosaurus and its ilk (marine animals are a different story – see “The whales’ tale”). The biggest land animal today is the African elephant, with a large male weighing in at around 6 tonnes. The largest land mammal ever was a 6-metre-tall hornless rhino known as Paraceratherium, which lived 30 million years ago and would have tipped the …