Schematic drawing of a subset of the animals that were studied as part of the study. Metabolic rates and the resulting thermophysiological strategies are color-coded, orange hues characterize high metabolic rates, coinciding with warm-bloodedness, and blue hues characterize low metabolic rates, coinciding with cold-bloodedness. From left to right: Plesiosaurus, Stegosaurus, Diplodocus, Allosaurus, Calypta (modern hummingbird). Credit: © J. Wiemann
Paleontologists have debated for decades whether dinosaurs are warm-blooded, like modern mammals and birds, or cold-blooded, like modern reptiles. Knowing whether dinosaurs are warm-blooded or cold-blooded can give us clues as to how active they were and what their daily lives were, but previous methods of determining their warm-bloodedness or cold-bloodedness – how quickly their metabolism can convert oxygen into energy – were unconvincing. However, in a new article published in the journal Nature, scientists unveiled a new method for studying the metabolic rates of dinosaurs, using clues in their bones that show how much the individual animals breathed in the last hour of their lives.
“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 Jasmina Viman, lead author. article and postdoctoral fellow at the California Institute of Technology (Caltech).
“The new proxy, developed by Jasmina Wiemann, allows us to directly lock the metabolism in extinct organisms, something we only dreamed of only a few years ago. We also found different metabolic rates that characterize different groups, which was previously suggested based on other methods, but has never been tested directly, “said Matteo Fabri, a postdoctoral fellow at the Field Museum in Chicago and one of the study’s authors.
People often talk about metabolism in terms of how easy it is to stay fit, but at its core, “metabolism is how efficiently we convert the oxygen we breathe into the chemical energy that feeds our body,” says Wiman, who is linked. with Yale University and the Los Angeles County Museum of Natural History.
Microscopic view of extracted soft tissues from the bones of one of the dinosaur specimens (Allosaurus), which were studied for metabolic signals (metabolic cross-links) in the fossil products of the protein bone matrix. Fossilization introduces additional cross-links that, in combination with metabolic cross-links, generate the characteristic brown color of the fossil extracellular matrix that holds bone cells (dark, branching structures) and blood vessels (tube-like structure in the center) in place. Credit: © J. Wiemann
Animals with a high metabolic rate are endothermic or warm-blooded; warm-blooded animals such as birds and mammals absorb a lot of oxygen and need to burn a lot of calories to maintain their body temperature and stay active. Cold-blooded or ectothermic animals such as reptiles breathe less and eat less. Their way of life is less energy expensive than that of high-blooded animals, but there is a price: cold-blooded animals rely on the outside world to keep their bodies at the right temperature to function (like a lizard that basks in the sun). and they tend to be less active than warm-blooded creatures.
Because the birds are warm-blooded and the reptiles are cold-blooded, the dinosaurs were caught in the middle of a debate. Birds are the only dinosaurs to survive the mass extinction at the end of the Cretaceous, but dinosaurs (and in addition birds) are technically reptiles – outside of birds, their closest living relatives are crocodiles and alligators. So will this make the dinosaurs warm-blooded or cold-blooded?
“It’s 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.” “Jasmine Wiman.”
Scientists have tried to determine the rate of metabolism of dinosaurs by chemical and osteohistological analysis of their bones. “In the past, people have looked at dinosaur bones with isotope geochemistry, which basically works as a paleothermometer,” says Viman. “It’s a really great approach and it was really revolutionary when it came out, and it continues to provide a lot of exciting insights into the physiology of missing animals. But we realized that we still don’t really understand how fossilization processes change the isotopic signals we capture, so it’s difficult to unambiguously compare fossil data with modern animals.
Another method of studying metabolism is growth rate. “If you look at a cross section of a dinosaur’s bone tissue, you can see a series of lines, like tree rings, that correspond to years of growth,” says Fabry. “You can count the lines of growth and the space between them to see how fast the dinosaur grows. The limitation depends on how you transform growth rate estimates into metabolism: faster or slower growth may have more to do with the stage of the animal’s life than with its metabolism, such as how we grow faster when we are young. and slower when we are older ”
The new method proposed by Wiemann, Fabbri and their colleagues does not look at the minerals present in bones or how fast a dinosaur has grown. Instead, they consider one of the main hallmarks of metabolism: the use of oxygen. When animals breathe, by-products are formed that react with proteins, sugars and lipids, leaving behind molecular “waste”. This waste is extremely stable and insoluble in water, so it is preserved during the petrification process. He leaves behind a record of how much oxygen the dinosaur inhaled and thus the rate of his metabolism.
We live in the sixth mass extinction, so it is important for us to understand how modern and extinct animals have reacted physiologically to past climate change and environmental disturbances, so that the past can inform biodiversity conservation in the present and inform our future actions. ”- Jasmina Wiman
Researchers have been looking for these molecular waste particles in dark-colored fossil femoral bones because these dark colors show that a lot of organic matter is preserved. They examined fossils using Raman-Fourier transform infrared spectroscopy – “These methods work like laser microscopes, we can basically quantify the abundance of these molecular markers that tell us about the rate of metabolism,” says Viman. “This is a particularly attractive method for paleontologists because it is non-destructive.
The team analyzed the femurs of 55 different groups of animals, including dinosaurs, their flying cousins pterosaurs, their more distant marine relatives plesiosaurs and modern birds, mammals and lizards. They compared the amount of respiratory molecular by-products with the known metabolic rates of living animals and used this data to infer the rate of metabolism of the extinct.
The team found that the rate of metabolism of dinosaurs is generally high. There are two large groups of dinosaurs, the Zaurischi and the Ornithishi – the thighs of lizards and the thighs of birds. Dinosaurs with bird thighs, such as triceratops and stegosaurus, had low levels of metabolism comparable to those of cold-blooded modern animals. Dinosaurs with lizard hips, including theropods and sauropods – two-legged, bird-like birds of prey such as Velociraptor and T. rex, and giant herbivores with long necks such as Brachiosaurus – were warm-blooded or even hot-blooded. Researchers were surprised to find that some of these dinosaurs are not just warm-blooded – they have metabolic levels comparable to modern birds, much higher than those of mammals. These results complement previous independent observations that hinted at such trends but could not provide direct evidence due to the lack of a direct proxy for the inference of metabolism.
These findings, researchers say, could give us fundamentally new insights into what dinosaur life was like.
“Dinosaurs with lower metabolic rates would be somewhat dependent on outside temperatures,” says Wiman. “Lizards and turtles sit in the sun and bask in the sun, and we may need to consider such” behavioral “thermoregulation in ornithis with extremely low metabolic rates. Cold-blooded dinosaurs may also have had to migrate to warmer climates during the cold season, and climate may have been a selective factor in where some of these dinosaurs might live.
On the other hand, she says, high-blooded dinosaurs would be more active and should eat a lot. “Giant-blooded giant sauropods were herbivores and will need a lot of plant matter to feed this metabolic system. They had a very efficient digestive system, and because they were so large, they probably had a bigger problem cooling down than warming up. ” .
“Reconstructing the biology and physiology of extinct animals is one of the most difficult things in paleontology. This new study adds a fundamental part of the puzzle to understanding the evolution of physiology in time and complements previous proxies used to study these issues. “We can now deduce body temperature through isotopes, growth strategies through osteohistology and metabolic rates through chemical substitutes,” says Fabbri.
As well as giving us an idea of what dinosaurs were like, this study also helps us better understand the world around us today. Dinosaurs, with the exception of birds, have disappeared en masse …
Add Comment