The increase in oxygen levels has allowed dinosaurs in North America to thrive, according to scientists

An old increase in oxygen levels has allowed dinosaurs in North America to flourish, scientists say.

A new technique of measuring gas levels in the early rocks shows that levels have jumped by nearly a third in a few million years.

Scientists say this could eventually allow Chindesauri and Sauropods to spread to the tropics of North America and elsewhere.

They presented the results at the Goldschmidt Geochemistry conference in Barcelona.

The researchers explained that they had developed a new technique to release very small amounts of gas trapped in ancient carbonate minerals.

The gases are then fed directly into a mass spectrometer, which measures their composition.

Scientists tested rocks of the Colorado Plateau and Newark Basin that were forming simultaneously about 1000 km from each other on the Pangea supercontinent.

They found that over a period of about three million years – which is very fast geologically – the rate of oxygen in the atmosphere has gone from about 15% to about 19%.

They use 21% oxygen in the current atmosphere for comparison.

Lead researcher Morgan Schaller, a professor at the Rensselaer Polytechnic Institute in New York, said: "We really do not know what may have caused this increase, but we also see a drop in CO2 levels at that time.

"We expect this change in oxygen concentration to have been a global shift and, in fact, we have found the change in samples 1000 km apart.

"What is remarkable is that at the top of the oxygen we see the first dinosaurs appear in the North American tropics, the Chindesaurus.

"The Sauropods followed soon after. "

He added that although they can not say it was about global development, dinosaurs did not impose themselves on ecological dominance in the tropics that they did not have. after the extinction of the final Trias.

Prof Schaller added: "What we can say is that it shows that the changing environment, 215 million years ago, was conducive to their evolutionary diversification, but that Oxygen levels may not have been the only factor. "

Chindesaurus was an erect carnivorous dinosaur measuring about 2 m long and nearly 1 m tall.

It was found widely in North America, with its origins in the tropics of North America, it was a characteristic dinosaur of the late Triassic Southwest.

The Sauropods, which appeared shortly after Chindesaurus, were the largest animals on the planet.

Professor Mike Benton, of Bristol University, commented on the study: "The first dinosaurs were quite small, but a high oxygen content in the atmosphere was often associated with a trend towards greater size.

"This new result is interesting because the timing of the rise in oxygen and the appearance of the dinosaurs is good, although the dinosaurs have become abundant in South America a little earlier, there are about 232 million of them. 39, years. "

At the time when the gases were trapped, the Colorado Plateau and the Newark Basin were part of the Pangea and were located near the equator.

Rocks containing oxygen and carbon dioxide have been dated by measuring the radioactive decay of uranium found in the samples.