To determine how Mamenchisaurus managed a neck as long as a semitrailer, Moore and colleagues used a CT scanner to analyse the animal’s vertebrae. Instead of being stuffed with heavy marrow and tissue while the dinosaur was living, the interior of the sauropod’s vertebrae were filled with large air pockets similar to those found in modern birds like storks and swans. These empty pockets accounted for up to 77 per cent of each bone’s volume, vastly decreasing the weight of Mamenchisaurus’ spine.

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Cary Woodruff, a palaeontologist at the Frost Science Museum in Miami who specialises in studying sauropods, said that lightening the neck’s load was essential for all sauropods. “Having such a long neck is a large weight that you have to position away from your body,” said Woodruff, who was not involved in the new study. “If you have to hold a hammer with your arm stretched out, your arm’s going to get tired pretty quick.”

Even though its vertebrae were hollow, Mamenchisaurus’ neck was far from frail. During the initial excavation, palaeontologists uncovered a fossilised rod of bony tissue several metres long. It may have been a stiff extension of the vertebra, often called cervical ribs, that would have run the length of the neck, bolstering its lightweight bones like a brace. While this reduced the flexibility of its neck, these ribs helped keep the sprawling structure stable.

“Even though it had a lot of bones, it wasn’t like a snake where it could curl up back on itself,” Woodruff said. “It was basically like a rod.”

With its reinforced spine, Mamenchisaurus most likely kept its neck horizontal at a relatively shallow angle above the ground. But because of how long its neck was, it could still pick leaves off the tops of many trees. This may have helped the sauropod squeeze into a unique niche in an ecosystem that was probably crowded with other gigantic herbivores.

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According to the researchers, several groups of sauropods appear to have evolved extremely long necks, which may have rivalled the crane-like projections of Mamenchisaurus.

“We don’t really know what the limits are because they continue to push them as we make more and more discoveries,” Moore said. “Our default should always be to assume that there’s something larger out there.”

This article originally appeared in The New York Times.