Comparison of Dinosaur body temperatures (Credit: Robin Dawson)

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The mysteries surrounding dinosaurs have fascinated generations of scholars and lay people alike. A group of Israeli scientists, led by Prof. Hagit Affek at the Hebrew University of Jerusalem’s Institute of Earth Sciences, has tackled one of the most pressing questions regarding the giant creatures that populated the earth for millions of years: whether dinosaurs were cold- or warm-blooded . The team’s research places them decisively in the second category.The issue has far-reaching implications. The latter group, also known as endothermic animals, can generate their own body heat, causing them to consume more energy but equipping them better against climate changes, while the former, exothermic animals, rely on the sun and external conditions for warmth – and at the same time, require less energy and therefore less food.As explained in a study published in Science Advances on Friday, the team employed an innovative method to measure historical temperatures, by analyzing chemical bonds among heavy isotopes in calcium carbonate minerals present in dinosaur egg shells. Known as clumped isotope geochemistry, this technique allows researchers to assess the temperature of the body of the mother who laid the egg. Through analyzing fossilized eggs from three species of dinosaurs, the scientists came to the conclusion that their body temperatures were between 35°-40°. Human body temperature usually ranges between 36.5°-37.5°.In order to determine whether the temperature was caused by warm climate conditions or by their own ability to regulate their body temperature, researchers selected a group of fossils from the cold region of Alberta, Canada, recorded temperature data from them, then analyzed the body temperatures of cold-blooded mollusks that lived in the same area during the time as the sampled dinosaurs.“The global climate during the dinosaur era was significantly warmer than it is today. 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,” Affek said.By applying the same isotope method to the mollusks’ shells, scientists assessed that their temperature measured around 26°, suggesting dinosaurs must have therefore been endothermic creatures, since otherwise their bodies would not have reached 35°.The team analyzed fossils from dinosaurs along the evolutionary path from exothermic reptiles to endothermic birds; however they argued that the change happened early on.“We believe that this transformation happened very early on in dinosaurs’ evolution, since the Mayasaura eggs – a lizard-like dinosaur species that we tested – were already able to self-regulate their body temperature, just like their warm-blooded, bird-like cousins, the Torrdons,” explained Affek.According to BBC, until recently, dinosaurs were believed to be cold-blooded in consideration of their close relationship with other reptiles. In 2014, however, a study published in the journal Science Studies claimed that they represented an intermediate category between reptiles and birds. The debate has been raging since then.The new research by Hebrew University will add a crucial contribution to it. And, as pointed out in the release presenting the research, it tells us that dinosaur parents should have worried if their baby got a fever.Robin R. Dawson and Pincelli M. Hull from Yale University, Daniel J. Field from the University of Cambridge, Darla K. Zelenitsky from the University of Calgary and François Therrien from the Royal Tyrrell Museum of Palaeontology, Drumheller, Alberta, are also coauthors of the study published in Science Advances.