Hot Or Not? Ancient Eggshells Reveal the Body Temperature of Dinosaurs

For 150 years, scientists have debated the nature of dinosaurs’ body temperatures and how they influenced activity levels.

To figure out the body temperatures of extinct dinosaurs, researchers analyzed calcium carbonate found in fossil eggshells. For quite awhile, most scientists believed dinosaurs were reptile-like-slow-moving, with low metabolic rates like modern-day crocodiles and alligators.

“This technique tells you about the internal body temperature of the female dinosaur when she was ovulating”, says Aradhna Tripati, a co-author of the study and a UCLA geologist.

On the other hand, Oviraptor, a theropod about 2 metres long and 35 kilograms in weight, had a body temperature around 32 °C.

The six Argentine eggshells were about 80 million years old and came from large, long necked titanosaur sauropods.

Sauropods’ body temperatures were warm-approximately 100 degrees Fahrenheit, according to the study.

The smaller dinosaur was substantially cooler, probably below 32C – but was probably able raise its temperature above that of its environment, said the team.

Warm blooded animals need to eat a lot to stay warm, necessitating hunts or eating plants.

Warm-blooded animals, or endotherms, typically maintain a constant body temperature while cold-blooded ones, called ectotherms, rely on external heat sources to warm up – like lizards lazing in the Sunday. Lizards, for example, often sit on rocks in the sun to absorb heat, which enables them to be more active. Previous studies have suggested scientists can determine the difference in dinosaurs by counting the carbon and oxygen isotopes in ancient bones and teeth. The research indicates that the answer could lie somewhere in between.

Depending on the temperature at which they formed, those materials contain different proportions of isotopes-atoms of the same chemical element that vary slightly in mass. But the technique works only if the material being analyzed is well-preserved, says Robert Eagle, an evolutionary biologist at the University of California, Los Angeles.

The new findings indicate that at least half of all dinosaurs possessed the ability to increase their body temperature through heat sources in the environment.

If dinosaurs were at least endothermic to a degree, they had more capacity to run around searching for food than an alligator would. This is the first time when dinosaur eggshells have been used to understand the body temperature and metabolism of dinosaurs. It’s not clear from the data, says Eagle, whether that boost came from an enhanced metabolism, behaviors such as basking in the sun, insulating layers of feathers or other material, or a few combination of these factors.

Titanosaurs could have elaborate systems to regulate their temperature the way modern birds and mammals do.

The team analysed the behaviour of two rare isotopes in calcium carbonate, a key ingredient in egg shells. A mineral that forms at colder temperatures will have more of these bonds than the same mineral formed at a higher temperature. Minerals forming inside colder bodies have more clustering of isotopes.

Even though modern birds and reptiles are separated from their dinosaur predecessors by millions of years, their eggshells are still built in roughly the same way. The research is based on fossilized eggshells previously discovered in Argentina and Mongolia.

Eagle, Tripati and colleagues published the first analysis of fossilized dinosaur teeth in the journal Science in 2011. Smaller, two-legged omnivorous oviraptors were estimated to have had a body temperature of 89.4 degrees Fahrenheit.