Elevated Levels of Oxygen Gave Rise to North American Dinosaurs, Scientists Say

A team of researchers from Rensselaer Polytechnic Institute and the University of Texas Austin has used a new technique to analyze tiny amounts of gas trapped inside 215-million-year-old rocks from the Colorado Plateau and the Newark Basin. Their results show that oxygen levels in these rocks leapt by nearly a third in just a couple of million years, possibly setting the scene for a dinosaur expansion into the tropics of North America and elsewhere.

Chindesaurus bryansmalli. Image credit: Petrified Forest National Park.

Chindesaurus bryansmalli. Image credit: Petrified Forest National Park.

“We tested rocks from the Colorado Plateau and the Newark Basin that formed at the same time about 621 miles (1,000 km) apart on the supercontinent of Pangea,” said Rensselaer Polytechnic Institute’s Professor Morgan Schaller, lead author of the study.

“Our results show that over a period of around 3 million years, the oxygen levels in the atmosphere jumped from around 15% to around 19%. For comparison, there is 21% oxygen in today’s atmosphere.”

“We really don’t know what might have caused this increase, but we also see a drop in carbon dioxide levels at that time.”

“We expect that this change in oxygen concentration would have been global change, and in fact we found the change in samples which were 621 miles apart,” he said.

“What is remarkable is that right at the oxygen peak we see the first dinosaurs appearing in the North American tropics, Chindesaurus.”

“The sauropods followed soon afterwards. Again, we can’t yet say if this was a global development, and the dinosaurs don’t rise to ecological dominance in the tropics until after the End-Triassic extinction.”

“What we can say is that this shows that the changing environment 215 million years ago was right for their evolutionary diversification, but of course oxygen levels may not have been the only factor.”

Chindesaurus was an upright carnivorous dinosaur, around 6.6 feet (2 m) long and nearly 3.3 feet (1 m) high. Found extensively in North America, with origins in the North American tropics, it was a characteristic Late Triassic dinosaur of the American Southwest.

“The first dinosaurs were quite small, but higher oxygen levels in the atmosphere are often associated with a trend to larger size,” said University of Bristol’s Professor Mike Benton, who was not involved in this research.

“This new result is interesting as the timing of oxygen rise and dinosaur appearance is good, although dinosaurs had become abundant in South America rather earlier, about 232 million years ago.”

Professor Schaller and colleagues presented their findings this week at the 2019 Goldschmidt Conference in Barcelona, Spain.

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M. Schaller et al. New constraints on ancient atmospheric oxygen concentrations and the Late Triassic rise of the first North American dinosaurs. Goldschmidt Abstracts 2019

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