Dinosaurs grew big to survive poor diet

DINOSAURS became so large because they did not get enough nitrogen in their diet, a scientist has claimed.

The essential nutrient is in all plants, and animals use it to manufacture proteins.

But 200 million years ago there was less of it in the atmosphere – and too much carbon dioxide – meaning giants like the brontosaurus survived by evolving into the biggest creatures that walked the planet.

As an animal's body size rises, its metabolic rate falls – along with the growth rate.

The lower an animal's metabolism and the slower its growth rate, the less protein and DNA it has to make – and the less nitrogen it will need per mouthful. An ecologist, Dr Jeremy Midgley, says sauropods such as brontosaurus – also now known as apatosaurus – weighed up to 100 tonnes and measured as much as 60m from head to tail because of this serious nitrogen deficiency.

Dr Midgley, of Cape Town University in South africa, said: "The average nitrogen content of most plants living then was typically lower.

"And then the carbon dioxide levels were much higher, maybe ten times today's. That suppresses the nitrogen content of plants even more."