Fearsome predators like T. rex and giant telescope-necked dinosaurs like Brachiosaurus were warm-blooded creatures just like birds and mammals, according to a groundbreaking new study.
The question of whether the blood flowing through the giant structures of dinosaurs was hot or cold, like that of reptiles, is a long-standing question that has irked paleontologists. Knowing this fundamental information could illuminate the lives of prehistoric creatures in significant ways.
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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 or cold-blooded is one of the oldest questions in paleontology, and we now think we have a consensus that most dinosaurs were warm-blooded.” . said the study’s lead author, Jasmina Wiemann, a postdoctoral researcher at the California Institute of Technology, in a press release.
Previous attempts to answer this question had suggested that dinosaurs were warm-blooded, but these findings, which involved analyzing growth rings or chemical isotope signals in the bones, were ambiguous because fossilization can alter these markers. In addition, these analysis techniques damage fossils, making it difficult to build a large dataset.
Wiemann and his colleagues, however, have devised a new – and in their opinion, more definitive – method for assessing a dinosaur’s metabolism.
Definitive answer?
The researchers analyzed the waste that forms 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 spots on fossils, scales with the amount of oxygen absorbed 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, meaning they are preserved during the fossilization process.
Wiemann and his team analyzed a femur – thigh bone – from 55 different creatures, including 30 extinct animals and 25 modern ones. Among the samples were bones belonging to dinosaurs, giant flying reptiles called pterosaurs, marine reptiles such as plesiosaurs, and modern birds, mammals and lizards.
The scientists used an approach called infrared spectroscopy, which targets interactions between molecules and light. This technique allowed them to quantify the number of residue molecules in the fossils. The team then compared these findings to 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 grouped dinosaurs with reptiles, leading to an assumption of a reptilian appearance and lifestyle. Today, most paleontologists agree that dinosaurs were much more bird-like after the discovery in the 1990s of feathered fossils, which led to the understanding that modern birds are directly descended from dinosaurs.
The study, published Wednesday in the journal Nature, found that dinosaurs’ metabolic rates were typically high, and in many cases higher, than modern mammals — which typically have a body temperature of around 37 degrees Celsius (98 degrees Fahrenheit). .6 degrees Fahrenheit) – and more. like birds, which have average body temperatures of around 42 degrees Celsius (107.6 degrees Fahrenheit).
“With our new evidence of an avian-level metabolism ancestral to all dinosaurs and pterosaurs, all warm-blooded dinosaurs likely had high body temperatures, comparable to modern birds,” Wiemann said by email.
However, there were notable exceptions. Dinosaurs classified as ornithischians — an order characterized by lizard-like hips that includes instantly recognizable creatures like Triceratops and Stegosaurus — evolved to have low metabolic rates comparable to those of modern, cold-blooded animals.
“Lizards and turtles sit in the sun and bask, and we may have to consider similar ‘behavioral’ thermoregulation in ornithischians with exceptionally low metabolic rates. may have been a selective factor for where some of these dinosaurs could live,” Wieman said.
Having a high metabolic rate has been proposed as one of the reasons birds survived the mass extinction that wiped out the dinosaurs 66 million years ago. However, Wiemann said this study indicated this was not true: many dinosaurs with exceptional bird-like metabolic abilities went extinct.
The research “will dramatically change” how the biology and behavior of many extinct animals are interpreted, said Jingmai O’Connor, associate curator of fossil reptiles at Chicago’s Field Museum. She was not involved in the study.
“I consider these results to be quite definitive. Wiemann’s methods are meticulous and have been extensively tested,” she said.
“Some dinosaurs were warm-blooded, this was the ancestral state, but others evolved secondarily to be ectothermic (cold-blooded). The next question to ask is why and what this means about their behavior, ecology and evolution.”
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