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Dinosaurs may have been warm-blooded, research from Yale suggests

A cross-sectional view of the Megaloolithus dinosaur eggshell using a petrographic microscope with cross-polarized light.
A cross-sectional view of the Megaloolithus dinosaur eggshell using a petrographic microscope with cross-polarized light.Robin Dawson

A study published in Science Advances last Friday examining dinosaur eggshells bolsters an emerging theory that the creatures were warm-blooded, not cold-blooded.

“Dinosaurs sit at an evolutionary point between birds, which are warm-blooded, and reptiles, which are cold-blooded,” lead author Robin Dawson, a postdoctoral research associate at the University of Massachusetts Amherst, told Yale News. “Our results suggest that all major groups of dinosaurs had warmer body temperatures than their environment.”

To conduct the study, researchers chose eggshell samples from three major dinosaur groups. The ordering of oxygen and carbon atoms in fossil eggshells is determined by temperature. The researchers used the ordering of the atoms to find the mother dinosaur’s body temperature. The method is known as clumped isotope paleothermometry.

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“There has been one study on teeth and one on eggshell, but we thought eggshells would have important information because they form close to the core of the body,” Dawson, who did the research while she was working toward her doctorate at Yale University, said in a telephone interview with the Globe.

Dawson and fellow researchers compared the eggshell temperatures of a small, meat-eating Troodon, a large, duck-billed Maiasaura, both found in Alberta, Canada, and another type of fossilized egg called Megaloolithus, found in Romania, with eggshell samples from known cold-blooded invertebrates that were in the same location as the dinosaur shells.

By comparing the shells using the technique, researchers said, they could determine the environment’s temperature and whether dinosaurs’ body temperatures were lower or higher than the environment.

“I think what’s special about our study is that we have context for the environment in which the animals were living, which is really important. … and that we had representative samples from all three major groups of dinosaurs,” Dawson told the Globe.

The Troodon dinosaur egg samples were found to be up to 18 degrees Fahrenheit warmer than the environment, the Maiasaura samples were up to 27 degrees warmer, and the Megaloolithus samples were up to 5.4 to 10.8 degrees warmer. Cold-blooded animals’ temperatures change frequently with the environment, but the eggshell samples were found to be consistently higher in temperature than the environment.

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“What we found indicates that the ability to metabolically raise their temperatures above the environment was an early, evolved trait for dinosaurs,” Dawson told Yale News.

Conducted over six years by Dawson and other Yale University researchers while she was a geology and geophysics doctoral student, the study provides evidence for the debate challenging the long-held belief that the Mesozoic creatures were cold-blooded.

A 2014 study published in the journal Science suggested that dinosaurs had rapid metabolisms not unlike mammals and birds, raising questions about the idea that dinosaurs were cold-blooded reptiles. Researchers found that dinosaurs’ metabolisms may have been in between fast and slow, in between cold-blooded and warm-blooded, making them mesothermic.

“When the effects of size and temperature are considered, dinosaur metabolic rates were intermediate to those of endotherms [warm-blooded] and ectotherms [cold-blooded] and closest to those of extant mesotherms,” the study said.

Matt Berg can be reached at matthew.berg@globe.com. Follow him on Twitter @mattberg33.