Chemical clues reveal dinosaur metabolism

Schematic diagram of a subset of animals examined as part of the study. Metabolic rates and the resulting thermophysiological strategies are color-coded, orange hues characterize high metabolic rates coinciding with warm-blooded bleeding, and blue hues characterize low metabolic rates coinciding with cold-blooded. From left to right: plesiosaur, stegosaurus, diplodocus, allosaurus, calypt (modern hummingbird). Credit: J. Wiemann

For decades, paleontologists debated whether dinosaurs were warm-blooded, like modern mammals and birds, or cold-blooded, like modern reptiles. Knowing whether dinosaurs were warm or cold-blooded can give us hints about how active they were and what their daily lives were, but ways to determine their warm or cold-blooded — how quickly their metabolic processes convert oxygen into energy — have been inconsistent. But in a new paper in temper natureScientists reveal a new way to study the metabolic rates of dinosaurs, using clues in their bones that indicate how much 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 palaeontology, and now we think we have a consensus that most dinosaurs were warm-blooded,” Yasmina Wehmann, author of the paper Principal and Postdoctoral Research Fellow at Caltech.

“The new agent developed by Jasmina Wiemann allows us to directly infer metabolism in organisms of genetics, something that we have only been dreaming about for a few years. We also found different metabolic rates characterizing different groups, which were previously proposed based on other methods,” says Matteo Fabri , a postdoctoral researcher at Chicago’s Field Museum and one of the study’s authors: “But it has never been tested directly.”

People sometimes talk about metabolism in terms of how easily a person stays in shape, but in essence, “metabolism is how effectively we convert the oxygen we breathe into chemical energy that fuels our bodies,” says Weiman, affiliated with the Yale University and Los County Museum of Natural History. Los Angeles.

Animals with a high metabolic rate are endothermic or warm-blooded. Warm-blooded animals such as birds and mammals consume a lot of oxygen and have to burn a lot of calories in order to maintain their body temperature and stay active. Cold-blooded animals such as reptiles breathe less and eat less. Their lifestyle is less expensive than that of warm-blooded animals, but it comes at a price: Cold-blooded animals depend on the outside world to keep their bodies at the right temperature to function (like a lizard basking in the sun), and they tend to be less active than warm-blooded creatures. .

With birds being warm-blooded and reptiles being cold-blooded, dinosaurs have been caught up in the debate. Birds are the only dinosaurs to survive the mass extinction at the end of the Cretaceous period, but dinosaurs (and thus birds) are technically reptiles—outside of birds, their closest relatives are crocodiles and crocodiles. Will this make dinosaurs warm-blooded or cold-blooded?

Scientists have attempted to extract the metabolic rates of dinosaurs from chemical and histological analyzes of their bones. “In the past, people would look at dinosaur bones using isotope geochemistry that basically works like an ancient thermometer,” Wiemann says, as researchers examine minerals in fossils and determine the temperatures at which those minerals would form. “It’s a really cool technique and it was really revolutionary when it came out, and it continues to provide very exciting insights into the physiology of extinct animals. But we realized that we don’t really understand yet how isotopic fossilization processes change the signals we pick up, so it’s unambiguously difficult to compare data from fossils. to modern animals.”

Another way to study metabolism is growth rate. “If you look at a cross-section of dinosaur bone tissue, you can see a series of lines, like tree rings, that correspond to years of growth,” Fabry says. “You can calculate growth lines and the distance between them to see how fast a dinosaur grew. Limit and how to convert growth rate estimates into metabolism: Growing faster or slower can have more to do with an animal’s stage of life than with metabolism, like how we grow faster when we’re young and slower when we are older.”

The new method proposed by Wyman, Fabry and their colleagues does not look at the minerals in the bones or how quickly dinosaurs grew. Instead, they look at one of the hallmarks of basic metabolism: the use of oxygen. When animals breathe, byproducts are formed that react with proteins, sugars and fats, leaving behind molecular “wastes”. This waste is very stable and insoluble in water, so it is preserved during the petrification process. It leaves behind a record of how much oxygen a dinosaur breathed, and therefore its metabolic rate.

Warm-blooded T. rex and cold-blooded stegosaurus: chemical evidence revealing dinosaur metabolism.

Microscopic view of soft tissue extracted from the bones of an Allosaurus specimen examined for metabolic cues (metabolic cross-links) in the ossified outgrowths of the protein bone matrix. Ossification introduces additional crosslinks that, in combination with metabolic cross-links, generate the characteristic brown color of the fossil extracellular matrix that keeps osteoblasts (branched dark structures) and blood vessels (tube-like structure in the center) in place. Credit: J. Wiemann

The researchers looked for these bits of molecular waste in dark-colored bone fossils, because those darker colors indicate that a lot of the organic matter is preserved. They examined the fossils using Raman and Fourier transform infrared spectroscopy—”these methods work like laser microscopes, we can basically determine the abundance of these molecular markers that tell us about the metabolic rate,” says Wiemann. “It’s a particularly attractive method for paleontologists, because it is non-destructive.”

The team analyzed the thighs of 55 different groups of animals, including dinosaurs, their flying cousins ​​pterosaurs, and their more distant marine relatives plesiosaurs, birds, mammals and modern lizards. They compared the amount of molecular byproducts associated with respiration with the known metabolic rates of living animals and used these data to infer the metabolic rates of extinct animals.

The team found that the dinosaurs’ metabolic rates were generally high. There are two large groups of dinosaurs, the saurischians and ornithischians – the lizard’s hip and the bird’s hip. Lizard-hiped dinosaurs, such as Triceratops and Stegosaurus, had lower metabolic rates similar to those of modern cold-blooded animals. Hip-hoped dinosaurs, including theropods and sauropods — legged, more bird-like predatory dinosaurs like Velociraptor and T-Rex, and giant long-necked herbivores like Brachiosaurus — were warm-blooded or even warm-blooded. The researchers were surprised to discover that some of these dinosaurs weren’t just warm-blooded—they had metabolic rates similar to modern birds, much higher than 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 metabolism inference.

The researchers say these findings could give us fundamentally new insights into what dinosaurs lived like.

“Dinosaurs with lower metabolic rates were somewhat dependent on outside temperatures,” Wyman says. “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.”

On the other hand, she says, warm-blooded dinosaurs were more active and had to eat a lot. “Giant, warm-blooded sauropods were herbivores, and it would take a lot of plant matter to fuel this metabolic system. They had very efficient digestive systems, and because they were so large, it probably was a problem for them to cool them down from heating.” Meanwhile, theropod dinosaurs – the group that includes birds – developed high metabolisms even before some of their members evolved to fly.

“Reconstructing the biology and physiology of extinct animals is one of the most difficult things to do in palaeontology. This new study adds an essential piece of the puzzle in understanding the evolution of physiology in ancient times and complements previous agents used to investigate these questions. We can Now infer body temperature through isotopes, growth strategies through bone morphology, and metabolic rates through chemical agents,” says Fabry.

In addition to giving us insight into what dinosaurs looked like, this study also helps us better understand the world around us today. Dinosaurs, with the exception of birds, died out in a mass extinction 65 million years ago when an asteroid hit Earth. “It has been suggested that a generally higher metabolic rate is one of the major advantages when it comes to surviving mass extinctions and succeeding in radiation afterward,” says Wyman, and some scientists have suggested that the birds survived while the non-avian dinosaurs died because of the birds. Increased metabolic capacity. But this study, Wiemann says, helps show that’s not true: Many dinosaurs with bird-like metabolic abilities became extinct.

“We are living in the sixth mass extinction, so it is important for us to understand how physiologically modern and extinct animals have responded to climate change and past environmental disturbances, so that the past can inform biodiversity conservation in the present and inform our future actions,” says Wyman.

The study indicates that dinosaurs were warm-blooded

more information:
Jasmina Wiemann, Fossil biomolecules reveal bird-like metabolism in dinosaur ancestors, temper nature (2022). DOI: 10.1038/s41586-022-04770-6.

the quote: Warm-blooded T. rex and Cold-blooded Stegosaurus: Chemical Evidence Revealing Dinosaur Metabolism (2022, May 25), Retrieved May 26, 2022 from -rex-cold -blood-stegosaurus-chemical. html

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