The question of whether dinosaurs were cold-blooded, like their reptilian relatives, or warm-blooded like their bird descendants, has long been debated in scientific circles.
Now, a team of Israeli researchers believes it has found evidence pointing to at least some of the ancient lizards being endotherms: warm-blooded animals.
Scientists at Hebrew University, led by Prof. Hagit Affek at the university’s Institute of Earth Sciences, used a new method, called clumped isotope geochemistry, to analyze chemical bonds in fossilized dinosaur eggs. The new technique allowed them to gauge the temperature in which calcium carbonate minerals, a major component of egg shells, were formed, and thus estimate the mother’s body temperature.
But this on its own would not be enough to reach a conclusion. After all, cold-blooded animals often warm themselves through exposure to sunlight and external heat sources.
“The global climate during the dinosaur era was significantly warmer than it is today,” Affek said. “For this reason, measuring only the body temperatures of dinosaurs who lived near the equator wouldn’t tell us whether they were endo- or exothermic because their body temperature may simply have been a cold-blooded response to the hot climates they lived in.”
And so the Israeli team checked fossils from Alberta, Canada, comparing the body temperature of cold-blooded mollusks with that of dinosaur species in the region. The mollusks exhibited a temperature of 26°C, in line with their known type of metabolism and temperatures at high latitudes.
But eggs tested from three different dinosaur species in the region showed that in all cases, the mother’s body temperature was between 35-40°C — a temperature characteristic of warm-blooded animals, and one the scientists said could not have been achieved in the cold northern regions but for the animal having an endothermic system.
Previous studies have posited that some dinosaurs may have been neither warm- nor cold-blooded exactly, but somewhere in between — able to produce heat internally and raise their body temperature, but not maintain it at a consistently high level, as mammals do.
Affek said this remained a possibility. But the important takeaway, she said, was the clear new evidence that the creatures could indeed keep themselves warm, even when their surroundings were decidedly less so.
She added that the team believed dinosaurs had evolved into warm-blooded creatures early on, noting that one of the species of eggs tested belonged to a Mayasaura, a dinosaur closer to cold-blooded lizards on the evolutionary tree, which also showed the results of a warm-blooded creature.
The study was published Friday in peer-reviewed journal Science Advances.