Was the dinosaurs’ blood hot or cold? The long-term question may finally have an answer

This image depicts, from the left, the approaching lizard, the stegosaurus, the double beam, the allosaurus and the cover (modern hummingbird), with red shades indicating warm-blooded and blue shades for cold-blooded. (J. Wiemann)

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ATLANTA – Terrifying predators such as T. rex and towering telescope-necked dinosaurs such as the brachiosaurus were warm-blooded creatures in much the same way as birds and mammals, according to a groundbreaking new study.

The question of whether the blood that flowed through the giant dinosaur frames was hot or cold, like that of reptiles, is a long-standing question that has plagued paleontologists. Knowing that fundamental information could illuminate the lives of prehistoric creatures in important ways.

Warm-blooded animals have a high metabolic rate – they take in a lot of oxygen and need a lot of calories to maintain their body temperature, while cold-blooded animals breathe and eat less.

“This is really exciting for us as paleontologists – the question of whether dinosaurs were warm-blooded is one of the oldest questions in paleontology and we now believe we have a consensus that most dinosaurs were warm-blooded,” he said. The study was co-authored by Jasmina Wiemann, a postdoctoral researcher at the California Institute of Technology, in a press release.

Recent attempts to answer this question suggest that the dinosaurs were warm-blooded, but these findings, which included the analysis of growth rings or chemical isotope signals in the bones, were ambiguous because fossilization could alter these markers. In addition, these analysis techniques damage the fossils, making it more difficult to create a large data set.

Wiemann and colleagues, however, have come up with a new – and in their view, more definitive – method for assessing a dinosaur’s metabolism.

Final answer;

The researchers looked at the waste that is formed when oxygen is inhaled into the body and reacts with proteins, sugars and lipids. The abundance of these waste molecules, which appear as dark-colored patches on fossils, is scaled according to the amount of oxygen ingested and is an indicator of whether an animal is warm-blooded or cold-blooded.

The molecules are also extremely stable and do not dissolve in water, which means that they are retained during the fossilization process.

Wiemann and her team analyzed a femur – femur – of 55 different creatures, including 30 extinct and 25 modern animals. Among the specimens were bones belonging to dinosaurs, giant flying reptiles called pterosaurs, marine reptiles such as near-lizards and modern birds, mammals and lizards.

The scientists used an approach called infrared spectroscopy, which targets the interactions between molecules and light. This technique allowed them to quantify the number of waste molecules in the fossils. The team then compared these findings with the known metabolic rates of modern animals and used this data to infer the metabolic rates of extinct creatures.

What they found

Previous generations of paleontologists had grouped dinosaurs with reptiles, leading to the hypothesis of a reptile appearance and way of life. Today, most paleontologists agree that dinosaurs were much more like birds after the discovery of winged fossils in the 1990s, which led to the understanding of modern birds directly by dinosaurs.

The study, published Wednesday in the journal Nature, found that dinosaurs’ metabolic rates were usually higher and in many cases higher than modern mammals – which typically have a body temperature of about 98.6 degrees Fahrenheit – and higher than birds. , which have an average body temperature of around 107.6 degrees Fahrenheit.

“With our new avian-level metabolism data from all dinosaurs and pterosaurs, all warm-blooded dinosaurs probably had high body temperatures comparable to those of modern birds,” Wiemann said in an email.

However, there have been notable exceptions. Dinosaurs classified as hens – a class characterized by lizard-like hips that include instantly recognizable creatures such as triceratops and stegosaurs – evolved to have low metabolic rates comparable to those of cold-blooded modern animals.

“Lizards and turtles sit in the sun and sunbathe and we may need to consider similar ‘behavioral’ thermoregulation in chickens with extremely low metabolic rates. Cold-blooded dinosaurs may also have to migrate to warmer climates during the cold season and the climate may “It was a selective factor in where some of these dinosaurs could live,” Wieman said.

Having a high metabolic rate has been suggested as one reason why birds survived the mass extinction of dinosaurs 66 million years ago. However, Wiemann said that this study showed that this was not true: many dinosaurs with excellent metabolic abilities such as birds became extinct.

The research will “drastically change” the way biology and behavior of many endangered animals are interpreted, said Jingmai O’Connor, associate curator of reptile fossils at the Field Museum in Chicago. He did not participate in the study.

“I think these results are quite definitive. Wiemann’s methods are meticulous and have been thoroughly tested,” he said.

“Some dinosaurs were warm-blooded, this was the ancestral state, but others secondary evolved into ectothermic (cold-blooded). The next question to be asked is why and what does this mean for their behavior, ecology and evolution?”

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