Mystery of how dinosaurs grew to be as big as buses is unravelled

How did dinosaurs grow to be as big as five-storey buildings? It’s all down to their bone structure - and a new study has thrown light on how they evolved their sturdy frames.

The study shows that dinosaurs evolved to have hollow bones with inner structures known as air sacs, which made their skeletons lighter and less dense.

These bone structures (which are very different to our dense, heavy bones) evolved separately at least three times, the study shows.

This shows how advantageous they were to the huge reptiles, the researchers say - and similar structures are still present in birds today.

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Lead author Tito Aureliano at the State University of Campinas's Institute of Geoscience said: "Less dense bones containing more air gave the dinosaurs and pterosaurs (and still give birds) more oxygen circulating in their blood, as well as more agility to hunt, flee and fight, or even to fly.

“They not only used less energy but also kept their bodies cool more efficiently.

Aureliano analysed fossilised bones from three Brazilian species of the Late Triassic (about 233 million years ago), the period in which the dinosaurs emerged.

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All the bones were found in recent decades in Rio Grande do Sul, Brazil's southernmost state.

Co-author Professor Fresia Ricardi-Branco said: "The Triassic was very warm and dry.

“What's now Rio Grande do Sul was far from the sea in the heart of the supercontinent Pangea. In that context, more oxygen circulating in the blood would cool the body more efficiently and certainly afford a welcome advantage, so much so that it evolved at least three times independently.”