Did Dinosaur Blood Run Hot or Cold? Both, according to a new study | CNN

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Were dinosaurs warm-blooded like birds and mammals or cold-blooded like reptiles? It’s one of paleontology’s oldest questions, and finding the answer is important because it sheds light on how prehistoric creatures lived and behaved.

Research over the past three decades has shown that some dinosaurs probably resembled birds, with feathers and perhaps the ability to generate their own body heat. .

However, it is difficult to find evidence that unequivocally shows what dinosaur metabolism was like. Clues from dinosaur eggshells and bones suggest that some dinosaurs were warm-blooded and others were not.

A new study published in the journal Current Biology on Wednesday suggested that three major dinosaur groups adapted differently to temperature changes, with the ability to regulate body temperature evolving in the early Jurassic period, about 180 million years ago.

Based on fossils of 1,000 dinosaur species and paleoclimate information, the new study looked at the distribution of dinosaurs across different environments on Earth during the dinosaur age, which began about 235 million years ago and ended 66 million years ago when an asteroid hit Earth collided.

Two of the three main groups – carnivorous therapod dinosaurs, including T. rex, and herbivorous ornithischians, whose notable members were Triceratops and Stegosaurus – spread out to live in colder climates during the Early Jurassic period, the research suggested. According to the study, these dinosaurs may have evolved endothermy, or the ability to generate body heat internally.

Sarah Meyssonnier/Reuters

Visitors view the skeleton of a giant Triceratops over 66 million years old, named ‘Big John’, on display ahead of its sale at the Drouot auction house in Paris in October 2021.

Therapods and ornithischians lived in a wide range of thermal landscapes in their respective evolutionary histories and were “remarkably flexible,” the researchers wrote. Recent fossil discoveries have shown that several species of dinosaurs even thrived in the Arctic, where they gave birth and lived year-round.

“Warm-blooded animals tend to be more active. Cold-blooded animals, for example, tend not to build nests,” says lead study author Dr. Alfio Alessandro Chiarenza, Royal Society Newton International Fellow at the Department of Earth Sciences, University College London.

In contrast, the towering, herbivorous sauropods continued to move to warmer areas at the planet’s lower latitudes, and the availability of richer foliage in certain habitats wasn’t the only factor why, the study found. Sauropods, including Brontosaurus and Diplodocus, also appeared to thrive in arid, savanna-like environments and practiced “long-term climate conservatism,” the researchers wrote.

“It fits well with what we imagine about their ecology,” Chiarenza said. “They were the largest land animals that ever lived. If they were warm-blooded, they probably would have overheated.”

Furthermore, he added, the amount of plant material they would have needed to consume if they were warm-blooded would have been unsustainable.

“(These animals) lived in herds and we know that each of them was the equivalent of ten African elephants. (If they were warm-blooded) they would only destroy plant life. As living animals, it makes more sense that they are more cold-blooded.”

However, Jasmina Wiemann, a postdoctoral researcher at the Field Museum of Natural History in Chicago, said the findings from this study contrasted with her own research, which looked at molecular traces of oxygen intake found in dinosaur fossils. Her 2022 research suggested that ornithischians were more likely cold-blooded and sauropods warm-blooded.

She wondered to what extent a dinosaur’s biogeographic range was determined by its metabolic capacity, as opposed to other factors such as behavior, growth strategy, feeding preferences and other ecological interactions.

“Some animals with incredibly fast growth rates (such as sauropods) and, if necessary, a fast metabolism, appear here to be cold-blooded, while other animals with very slow growth rates (such as ceratopsians) are found as endotherms,” says Wiemann. said. “These disparities need to be addressed.”

Chiarenza said the model, developed by researchers from UCL and the Universidade de Vigo in Spain, suggested the earliest dinosaurs were more reptilian and cold-blooded. But a period of global warming due to volcanic activity 180 million years ago, known as the Jenkyns event, may have been a trigger for the evolution of the ability to generate body heat internally.

“Many new dinosaur groups emerged at that time. The adoption of endothermy, perhaps a consequence of this environmental crisis, may have allowed theropods and ornithischians to thrive in colder environments, allowing them to be highly active and sustain their activity for longer periods, develop and grow faster, and more could produce offspring,” he added. said in a press release.

As with all model-based research, the study made predictions based on existing information. New fossils or climatological information can change that picture. “If a sauropod were to show up in the Arctic, that would obviously change things,” Chiarenza said.

Paleontologist Anthony Fiorillo, executive director of the New Mexico Museum of Natural History & Science, said the study was “intriguing” and the “first real attempt to quantify broad patterns that some of us had previously thought about.” Fiorillo, who is also a senior fellow at Southern Methodist University in Dallas, was not involved in the study.

“Their models help create robustness in our biogeographical understanding of dinosaurs and their related physiology,” he said.

“This study gives us a platform to further test what we think we know.”

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