How Hot Were Dinos? Eggshells Reveal

Dinosaur body temperatures widely varied, according to a new study that used dino eggshells to determine how hot, or not, some dinosaurs were.

The new research in the journal Nature Communications, represents the first time that dinosaur eggshells have been used to figure out the body temperature and metabolism of dinosaurs.

The research concluded that titanosaurs -- huge long-necked, plant-eating dinosaurs -- were hotter than humans, measuring out at 99.7 degrees Fahrenheit. Smaller, two-legged omnivorous oviraptors were estimated to have had a body temperature of 89.4 degrees Fahrenheit.

"Many people now think, based on current work, that dinosaurs were either fully endothermic (warm-blooded and producing heat internally) like most modern mammals and birds, or at a kind of intermediate physiological state and had not reached full endothermy," explained lead author Robert Eagle, who is a researcher at the University of California at Los Angeles' Institute of the Environment and Sustainability.

Eagle, who is also LabEx International Chair of the European Institute of Marine Sciences, and his colleagues measured the bonds between two heavy isotopes, Carbon-13 and Oxygen-18, in the calcium carbonate mineral that makes up the hard part of eggshells.

He explained, "The abundance of these bonds in calcium carbonate is related to the temperature the mineral forms at, with more bonds forming at cold temperatures and less at hot. In the case of eggshells, the abundance of these bonds reflects the body temperature of the female when the eggshell forms."

The scientists took the measurements for both eggs of living dinosaurs, i.e. birds, as well as for eggs of now-extinct dinosaurs. Several eggs did not retain their original chemical composition, but the researchers believe they did get accurate readings for titanosaurs and oviraptors.

Both types of dinosaurs lived during the Upper Cretaceous roughly 70-80 million years ago.

Eagle and his team suspect that titanosaurs and other sauropods were warmer because of their size and apparent slow metabolism. The scientists point out that some large modern leatherback turtles are known to have elevated body temperatures as a result of their size.

The researchers quickly add, however, that many factors can affect an animal's body temperature. The presence of fur or a lot of feathers is one thing can influence body temperature. The average metabolic rate of the species is another big factor. Large animals are therefore not always the hottest.

In terms of today's birds, Eagle said "smaller birds tend to have hotter body temperatures than larger birds. Small birds like the hummingbird, for example, expend a lot of energy in their flight, while big flightless birds have lower body temperatures and metabolic rates. It shows how complicated metabolism and thermal regulation can be!"

Steve Brusatte of the University of Edinburgh's School of GeoSciences did not work on the new study, which he told Discovery News "is pushing the boundaries of the field."

He continued, "Eggshells may seem like a weird way to study the metabolism of dinosaurs, but they can be a very valuable source of evidence, because eggshells form at the same body temperature as the mother, and body temperature is critical to understanding the physiology of an animal."

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