A long-standing question — were dinosaurs cold-blooded or warm-blooded creatures? — may have been answered, researchers say, and the answer appears to be yes. To both.
Scientists using fossilized dinosaur eggshells to determine the body temperatures of dinosaur species say they varied widely, with some having body temperatures even warmer than humans.
For 150 years, paleontologists have debated the question of dinosaur body temperature and how that would impact their activity levels.
Were they fast, active and aggressive hunters, or did they move more slowly like modern-day crocodiles and alligators?
Analysis of the chemistry of fossilized eggshells from Mongolia and Argentina revealed under what temperature they formed, the researchers report in the journal Nature Communications.
"This technique tells you about the internal body temperature of the female dinosaur when she was ovulating," explains study co-author Aradhna Tripati, a UCLA assistant professor of geology, geobiology and geochemistry. "This presents the first direct measurements of theropod body temperatures."
One species of titanosaurs — giant long-necked herbivorous dinosaurs — had body temperatures of 99.7 degrees Fahrenheit, warmer than the 98.6 average for humans, the researchers determined.
In contrast, some smaller omnivorous two-legged oviraptors possessed a body temperature of 89.4 degrees.
While that's warmer than some modern crocodiles and their relatives, it suggests their physiology was not fully warm-blooded — known as endothermic — and they still needed to elevate their body temperature using environmental heat sources such as sunlight, as modern cold-blooded species do.
Endothermic species produce heat internally to maintain body temperature regardless of the temperature of their surroundings, while cold-blooded creatures — ectotherms — require some external sources.
So, in the question of warm-blooded versus cold-blooded — at least in the case of dinosaurs — the study suggests the answer may lie somewhere in between, the researchers say.
The oviraptors, though not fully endothermic, apparently possessed the ability to raise their body temperature to at least slightly above that of their environment, they report.
Still, they had lower body temperatures than modern birds, their only living relatives, and were probably less active, they add.
"The temperatures we measured suggest that at least some dinosaurs were not fully endotherms like modern birds," says study leader Robert Eagle of UCLA's department of earth, planetary and space sciences. "They may have been intermediate — somewhere between modern alligators and crocodiles and modern birds; certainly that's the implication for the oviraptorid theropods."
Even being slightly endothermic would have given the oviraptors a greater capacity to move around in search of food than a modern alligator, he says.
Both of the species studied — titanosaurs and oviraptors — lived around 70 to 80 million years ago during the Upper Cretaceous period.
