Dinosaurs appeared on Earth about 230 million years ago, when atmospheric oxygen levels were close to half what they are today. Scientists wonder how they survived – for 165 million years – under these varying conditions.
UC Irvine biologist James Hicks is finding answers in the alligator, a modern relative of the dinosaur.
In a recent study, Hicks and UCI postdoctoral researcher Tomasz Owerkowicz found that alligators incubated and raised in an environment with just 12 percent oxygen (compared to today’s 21 percent) had larger hearts and lungs and improved cardiopulmonary function.
“In a similar vein, the success of dinosaurs probably depended on the effectiveness of their lungs and hearts in obtaining oxygen from air and distributing it throughout the body,” Hicks says. “Our results provide indirect evidence that dinosaurs must have had superior oxygen delivery systems.”
Such findings are important because the Earth’s atmosphere is changing: Oxygen levels are dropping, while carbon dioxide levels are rising.
“Our experiments may help us understand how some animals will be able to adapt to environmental change in the near future,” Hicks says. “They may help us identify which animals are likely to survive and which might become extinct in new atmospheric conditions.”
Hicks has been awarded about $407,000 over three years from the National Science Foundation for this work, paired with about $180,000 to colleagues at California State University campuses in Long Beach and San Bernardino. The grant will begin Aug. 15.
Large reptiles such as alligators have existed in their basic form for about 220 million years, surviving large oxygen fluctuations. To study how they adapt, Hicks and Owerkowicz incubated alligator eggs at different oxygen levels – 12 percent, 21 percent and 30 percent (Earth’s peak level, occurring about 300 million years ago).
Hatchlings from the two higher-oxygen groups had no obvious physical differences, but those from the oxygen-starved group had swollen bellies. Researchers believe there was not enough oxygen for the developing embryos to consume all of their egg-yolk food, leaving them with huge yolk-distended potbellies. They also were smaller, except for their hearts, which were large, presumably to maximize the limited oxygen supply.
After three months in their respective atmospheres, the low-oxygen alligators had compensated by developing enlarged lungs, resulting in an increased metabolic rate.
“The metabolic rate determines everything an animal is capable of doing – running, digesting, keeping warm, growing and reproducing,” Owerkowicz says. “The basic function of alligators – the resting metabolic rate – was different just because the oxygen level was different.”
The study appeared in the Journal of Experimental Biology.