The question of whether the blood that ran through the giant bodies of dinosaurs was hot or cold, like that of reptiles, is a long-standing question that has puzzled paleontologists. Knowing that fundamental information could illuminate the lives of prehistoric creatures in significant 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 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. hot”. study lead author Jasmina Wiemann, a postdoctoral researcher at the California Institute of Technology, said in a news 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 bones, were equivocal because fossilization can change these markers. Furthermore, those analysis techniques damage the fossils, making it difficult to create a large data set.
However, Wiemann and his colleagues devised a new, and in their opinion, more definitive, method for assessing a dinosaur’s metabolism.
The researchers looked at the waste products that are formed when the body takes in oxygen and reacts with proteins, sugars and lipids. The abundance of these debris molecules, which appear as dark-colored spots on fossils, scales according to 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, which means that they are preserved during the fossilization process.
Wiemann and his team analyzed an femur – thigh bone – from 55 different creatures, including 30 extinct and 25 modern animals. 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 focuses on the interactions between molecules and light. This technique allowed them to quantify the number of debris molecules in the fossils. The team then compared those findings to known metabolic rates of modern animals and used that data to infer the metabolic rates of extinct creatures.
what they found
Previous generations of paleontologists had lumped dinosaurs with reptiles, leading to assumptions 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.
“With our new evidence of an avian-level metabolism ancestral to all dinosaurs and pterosaurs, all warm-blooded dinosaurs probably had high body temperatures, comparable to those of modern birds,” Wiemann said by email.
However, there were notable exceptions. classified dinosaurs such as ornithischians, an order characterized by lizard-like hips that includes instantly recognizable creatures like Triceratops and Stegosaurus — it evolved to have low metabolic rates comparable to those of modern cold-blooded animals.
“Lizards and tortoises sit in the sun and bask, and we may have to consider similar ‘behavioural’ thermoregulation in ornithischians with exceptionally low metabolic rates. Cold-blooded dinosaurs might also have had to migrate to climates warmer during the cold season, and climate may have been a selective factor in where some of these dinosaurs might live,” Wieman said.
It has been proposed that having a high metabolic rate is one of the reasons birds survived the mass extinction that wiped out the dinosaurs 66 million years ago. However, Wiemann said this study indicated that this was not true: Many dinosaurs with exceptional bird-like metabolic abilities went extinct.
The research will “dramatically change” the way the biology and behavior of many extinct animals are interpreted, said Jingmai O’Connor, associate curator of fossil reptiles at the Field Museum in Chicago. She did not participate in the study.
“I think these results are pretty definitive. Wiemann’s methods are painstaking and have been thoroughly tested,” he said.
“Some dinosaurs were warm-blooded, this was the ancestral state, but others evolved secondarily to be ectothermic (cold-blooded). The next question we need to ask ourselves is why and what does this mean about their behavior, ecology, and evolution”.