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Were dinosaurs warm-blooded like birds and mammals or cold-blooded like reptiles? It’s one of the oldest questions in paleontology, and getting the answer is important because it sheds light on how prehistoric creatures may have lived and behaved.
Challenging the prevailing idea that they were all slow, clumsy lizards that basked in the sun to regulate their body temperature, research over the past three decades has revealed that some dinosaurs were probably bird-like, with feathers and perhaps the ability to generate their own body heat. .
However, it is difficult to find evidence that unquestionably shows what dinosaur metabolism was like. Clues dinosaur eggshells It is bones suggested that some dinosaurs were warm-blooded and others were not.
A new study published in the journal Current Biology on Wednesday suggested that three main groups of dinosaurs adapted differently to temperature changes, with the ability to regulate body temperature evolving at the beginning of the Jurassic Period, around 180 million years ago. years.
Based on fossils from 1,000 dinosaur species and paleoclimatic information, the new study analyzed the spread of dinosaurs in different environments on Earth throughout the age of dinosaurs, which began about 235 million years ago and ended 66 million years ago, when an asteroid fell to Earth.
Two of the three main groups – carnivorous theropod dinosaurs, which included T. rex, and herbivorous ornithischians, whose notable members included Triceratops and Stegosaurus – spread to live in colder climates during the early Jurassic Period, it has been suggested. the investigation. These dinosaurs may have developed endothermy, or the ability to generate body heat internally, according to the study.
Two groups of adaptable dinosaurs
Therapods and ornithischians lived in a wide range of thermal landscapes in their respective evolutionary histories and were “remarkably adaptable,” the researchers wrote. Recent fossil discoveries have shown that different dinosaur species thrived even in the Arctic, giving birth and living there year-round.
“Warm-blooded animals are generally more active, for example cold-blooded animals generally do not build nests,” said study lead author Dr Alfio Alessandro Chiarenza, Royal Society Newton International Fellow in the department of Earth sciences at University College London.
In contrast, the towering herbivorous sauropods remained in warmer, low-latitude regions of the planet, and the availability of richer foliage in certain habitats was not the only factor, the study concluded. Sauropods, which included Brontosaurus and Diplodocus, also appeared to thrive in arid, savanna-like environments and practiced “prolonged climate conservatism,” the researchers wrote.
“This reconciles well with what we imagine about their ecology,” Chiarenza said. “They were the largest land animals that ever existed. They probably would have overheated if they were warm-blooded.”
What’s more, he added, the amount of plant matter they would need to consume if they were warm-blooded would have been unsustainable.
“(These animals) lived in herds and we know that each of them was equivalent to 10 African elephants. (If they were warm-blooded) they would simply destroy plant life. It makes more sense, as living animals, that they would be more cold-blooded.”
However, Jasmina Wiemann, a postdoctoral researcher at Chicago’s Field Museum of Natural History, said this study’s findings contrast with her own research, which looked at molecular traces of oxygen ingestion found in dinosaur fossils. Her 2022 Study suggested that ornithischians were more likely cold-blooded and sauropods were warm-blooded.
She questioned the extent to which a dinosaur’s biogeographic range was determined by its metabolic capacity as opposed to other factors such as behavior, growth strategy, dietary preferences and other ecological interactions.
“Some animals with incredibly fast growth rates (i.e., sauropods) and, by necessity, fast metabolisms, are here considered cold-blooded, while other animals with very slow growth rates (i.e., ceratopsians) are considered endotherms.” , Wiemann said. “These discrepancies will need to be addressed.”
Evolutionary trigger
Chiarenza said the model, developed by researchers at UCL and the University of Vigo in Spain, suggested that the first dinosaurs were more reptilian and cold-blooded. But a period of global warming resulting from 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.
“At this time, many new groups of dinosaurs appeared. The adoption of endothermy, perhaps a result of this environmental crisis, may have allowed theropods and ornithischians to thrive in colder environments, allowing them to be highly active and maintain activity for longer periods, develop and grow more quickly, and produce more offspring. “, he said. said in a press release.
As with all model-based research, the study made predictions based on existing information. New fossils or climate information could change this picture. “Of course, if a sauropod appeared in the Arctic that would change things,” Chiarenza said.
Paleontologist Anthony Fiorillo, executive director of the New Mexico Museum of Natural History and Science, said the study was “intriguing” and the “first real attempt to quantify broad patterns that some of us have previously thought about.” Fiorillo, who is also a senior researcher at Southern Methodist University in Dallas, was not involved in the research.
“Their modeling helps build robustness to our biogeographic understanding of dinosaurs and their related physiology,” he said.
“This study provides a platform for us to further test what we think we know.”
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