Clues reveal the metabolic rate of dinosaurs: warm-blooded Tyrannosaurus rex, cold-blooded Stegosaurus!

For decades, paleontologists have debated whether dinosaurs were warm-blooded, like modern mammals and birds, or cold-blooded, like modern reptiles. Knowing whether dinosaurs were warm-blooded or cold-blooded can give us hints about how active they were and what their day-to-day lives were like. In a new paper in the journal Nature, scientists reveal a new way to study the metabolic rate of dinosaurs using clues in their bones.

"This is really exciting for us as paleontologists - the question of whether dinosaurs were warm- or cold-blooded is one of the oldest in paleontology, and now we think we're in agreement, that most dinosaurs were warm-blooded," said Jasmina Wiemann, lead author of the paper and a postdoctoral researcher at the California Institute of Technology.

Dinosaur bones are clues to studying the metabolic rate of dinosaurs.

"The new proxy developed by Jasmina Wiemann allows us to directly infer metabolism in extinct organisms, something we've always dreamed of before." Matteo Fabbri, a postdoctoral researcher at the Field Museum in Chicago and one of the study's authors, says different metabolic rates are specific to different groups.

People sometimes talk about metabolism the way one easily stays in shape, but at its core, "metabolism is how we efficiently convert the oxygen we breathe into energy." chemistry that powers the body," said Wiemann, associate professor with Yale University and the Los Angeles County Museum of Natural History.

The lifestyle of cold-blooded animals is less energy-intensive than that of warm-blooded animals. (Illustration).

Animals with a high metabolic rate are endothermic, or warm-blooded; Warm-blooded animals like birds and mammals take in a lot of oxygen and have to burn a lot of calories to maintain body temperature. Cold-blooded animals, like reptiles, breathe less and eat less than warm-blooded animals. Their lifestyle is less energy-intensive than warm-blooded animals, but they must depend on the outside world to keep their bodies at the right temperature to function (like a lizard basking in the sun). sun), and they tend to be less active than warm-blooded organisms.

With birds being warm-blooded and reptiles cold-blooded, dinosaurs were caught in the middle of a debate. Birds were the only dinosaurs that survived the mass extinction of the late Cretaceous, but dinosaurs were essentially reptiles. So that's realistic, were dinosaurs warm-blooded or cold-blooded?

Dinosaurs are warm-blooded or cold-blooded animals?

Scientists have been trying to gather the dinosaur's metabolic rate from chemical and backbone analyzes of their bones. "In the past, people have looked at dinosaur bones with isotope geochemistry that behaves like a classical thermometer," says Wiemann - researchers examine the minerals in a fossil and determine the temperature. that these minerals will form. But we realized that we don't really understand how fossils change isotopic signals, so it's difficult to clearly compare data from fossils with modern animals."

Instead, they looked at one of the most basic markers of metabolism: oxygen utilization. When animals breathe, by-products of reactions with proteins, sugars and lipids are formed, leaving behind molecular "waste". This waste is very stable and insoluble in water, so it is stored in petrochemical processes. It records the amount of oxygen the dinosaur inhaled, and thus its metabolic rate.

The researchers looked for bits of these molecular waste in dark-colored fossil females, because those dark colors indicate that a lot of organic matter was preserved. They examined the fossils using Raman and Fourier transform infrared spectroscopy - "these methods work like laser microscopy, we can essentially quantify the abundance of molecules and know on metabolic rate," says Wiemann.

The team analyzed samples from 55 different animal groups, including king dinosaurs, pterosaurs, plesiosaurs, and modern birds, mammals and lizards. They compared the amount of molecular by-products involved in respiration with the known metabolic rates of living animals and used those data to infer the metabolic rates of extinct species.

Tỷ lệ trao đổi chất của khủng long nói chung là cao.

Nhóm nghiên cứu phát hiện ra rằng tỷ lệ trao đổi chất của khủng long nói chung là cao. Có hai nhóm khủng long lớn, saurischians và ornithischians - hông thằn lằn và hông chim. Các loài khủng long chân chim, như Triceratops và Stegosaurus, có tỷ lệ trao đổi chất thấp tương đương với các loài động vật máu lạnh hiện đại.

Khủng long mỏm thằn lằn, bao gồm các loài khủng long săn mồi hai chân như Velociraptor, T. rex và động vật ăn cỏ cổ dài, khổng lồ như Brachiosaurus đều là những loài động vật máu nóng - chúng có tỷ lệ trao đổi chất tương đương với các loài chim hiện đại, cao hơn nhiều so với động vật có vú.

The discovery could provide a fundamental understanding of how dinosaurs lived, the researchers say. Reconstructing the biology and physiology of extinct animals is one of the most difficult tasks in paleontology. The new study was able to infer body temperature from isotopes, growth strategies from bone histology, and metabolic rate from chemicals.

Understanding how modern and extinct animals physiologically respond to previous climate changes and environmental disturbances is crucial to being able to inform them, the researchers say. biodiversity conservation now and inform future human actions.