The question of whether the blood flowing through the giant frames of dinosaurs was warm or cold, like reptiles, is a long-standing question that has irritated paleontologists. Knowing that a key piece of information can illuminate the lives of prehistoric creatures in important ways.
Warm-blooded animals have a high metabolism – they take in a lot of oxygen and need many 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 palaeontology, and now we think we have a consensus, that most dinosaurs were warm-blooded,” said the study’s lead author. Yasmina Wiemann, a postdoctoral researcher at the California Institute of Technology, said in a press release.
Previous recent attempts to answer this question suggested that dinosaurs were warm-blooded, but those findings, which involved analysis of growth rings or chemical isotope signals in the bones, have been ambiguous because fossilization might alter these markers. In addition, these analysis techniques damage the fossils, making it difficult to generate a large set of data.
However, Weiman and her colleagues have come up with a new – and in their view – more specific way to assess dinosaur metabolism.
The researchers looked at the waste products that form when oxygen is inhaled into the body and interact with proteins, sugars and fats. The abundance of these waste particles, which appear as dark-colored spots in the fossils, is proportional to the amount of oxygen ingested and is an indication of whether the animal is warm- or cold-blooded.
The molecules are also very stable and do not dissolve in water, which means that they are preserved during the petrification process.
Wieman and her team analyzed a Femur – the femur – from 55 different creatures, including 30 genetics and 25 recent animals. Among the specimens are the bones of dinosaurs, giant flying reptiles called pterosaurs, marine reptiles such as plesiosaurs, birds, modern mammals and lizards.
The scientists used a method called infrared spectroscopy, which targets interactions between molecules and light. This technique allowed them to determine the number of waste particles in the fossils. The team then compared these results to known metabolic rates of modern animals and used those data to infer the metabolic rates of the extinct creatures.
what they found
Previous generations of paleontologists had combined dinosaurs with reptiles, which led to the postulation of the appearance and lifestyle of reptiles. Today, most paleontologists agree that dinosaurs were more bird-like after the discovery of feathered fossils in the 1990s, which led to the understanding that modern birds are directly descended from dinosaurs.
“With our new evidence of the existence of metabolic ancestors at the bird level for everyone Dinosaurs, pterosaurs, and all warm-blooded dinosaurs likely had high body temperatures, similar to those of modern birds,” Wyman said by email.
However, there were notable exceptions. classification of dinosaurs such as ornithischians – an arrangement characterized by lizard-like buttocks that includes instantly recognizable creatures such as triceratops and stegosaurus – They evolved to have low metabolic rates similar to those of cold-blooded animals.
“Lizards and turtles sit in the sun and bask, and we may have to think of similar ‘behavioural’ thermoregulation in birds with exceptionally low metabolic rates. Cold-blooded dinosaurs may also have to migrate to warmer climates during the cold season and climate may have been a selective factor. for where some of these dinosaurs could live.”
A high metabolic rate has been suggested as one reason birds survived the mass extinction that wiped out the dinosaurs 66 million years ago. However, Wieman said this study suggests that this wasn’t true: Many dinosaurs with bird-like metabolic abilities passed down genetics.
Jingmaye O’Connor, associate curator of fossil reptiles at Chicago’s Field Museum, said the research would “drastically change” how we explain the biology and behavior of many extinct animals. She did not participate in the study.
“I consider these results to be largely conclusive,” she said. “Weiman’s methods are accurate and have been rigorously tested.”
“Some dinosaurs were warm-blooded, and this was the ancestral state, but others secondary evolved to be extrathermophilic (cold-blooded). The next question to ask is why and what this means for their behavior and environment, and evolution.”