Dinosaurs are warm-blooded or cold-blooded?

By Shorouk Al-Ashqar

Scientists have long wondered why the metabolic rate of birds was so high, and there was no better path to understanding this phenomenon than studying the ancestors of these animals, which opened the door to studying the metabolic rates of dinosaurs, since they represented the ancient ancestor of birds living today. Credit: J. Wiemann

Living organisms have different natures in the way they adapt to the surrounding environment; Birds keep their bodies warm through the heat generated by some metabolic processes, while lizards and reptiles rely on the sun’s heat to keep them warm. Both groups – taxonomically – are closely related to dinosaurs, which is why for decades there has been a debate among paleontologists about the nature of dinosaur bodies. And being a warm-blooded animal like its descendants from birds, or a cold-blooded one like its cousins, reptiles and crocodiles.

Deducing the physiology of the special metabolic processes and their speed in converting oxygen into energy for an extinct animal that lived and died millions of years ago is very difficult and complex, but it helps a lot in determining the activity of this organism and how its daily life was.

In this context, a new study published in the journal Nature reveals new ways to study the metabolic rates of dinosaurs, using scientific evidence in their fossilized bones that show how much these animals breathed during the last hour of their lives, and reveals that the first dinosaurs as well as flying reptiles were all living creatures. Warm-blooded, then began to vary between warm-blooded and cold-blooded over time.

“Our current study confirmed previous assumptions that the first dinosaurs and flying reptiles were warm-blooded, but the current study’s finding of accurate metabolic rates in dinosaur groups is astonishing,” says Jasimena Wiemann, lead author of the study.

Weiman added, in statements to “Science”: I think that one of the most complex aspects of reconstructing the metabolism of dinosaurs is how to link the different lines of evidence, including metabolic rates, body temperatures, and growth rates, and so we believe that in our study we found this link between all Evidence, which describes the metabolic rate and the amount of oxygen an organism breathes in and converts into chemical energy.

“As part of this conversion, some energy is released in the form of heat, and different biochemical mechanisms are responsible for this energy leakage in different groups of organisms,” she explained.

Hot and cold blooded dinosaurs

Metabolism – or what is known as “metabolism” – is one of the most important biological processes in the bodies of living organisms; It is responsible for maintaining the living condition of cells and tissues through a series of biochemical reactions that work primarily to convert food into energy, by breaking down nutrients within the digestive system and converting them into vital energy.

Mammals and birds are the most complex animals in the process of metabolism, while birds have the highest rate of metabolism among all animals living today, and scientists have always wondered about the secret of this high rate of metabolism in birds, and there was no path for scientists to understand this biological phenomenon better than Going back in time to study the ancestors of these animals, which opened the door to studying the metabolic rates of dinosaurs, as they represented the ancient ancestor of the birds that live today.

Birds are “living dinosaurs”, the only ones that survived the mass extinction at the end of the Cretaceous period, and studying the metabolic rate of dinosaurs is important, not only because it will explain the high metabolic rates in birds today, but also because it will undoubtedly give concrete evidence of whether dinosaurs were Warm-blooded (they have a high metabolic rate and can regulate their body temperature) or cold-blooded (they have a low metabolic rate and depend on an external source for heating their bodies).

Birds are the only living animals that are generally considered warm-blooded (a quasi-constant body temperature of about 42°C), mammals (which includes us humans with a near-constant body temperature of about 37°C), and reptiles are cold-blooded, with Since birds are warm-blooded and reptiles are cold-blooded, dinosaurs have fallen into a great scientific debate!

A thermometer preserved in fossil bones

Scientists used several methods to study the metabolic rates of dinosaurs, including geochemical methods represented in the signals of chemical isotopes, which are considered an “old thermometer”, so to speak, in studying the fossils of dinosaur bones to infer some ancient biological processes, and although it gives amazing results and revealed many The secrets about the life of dinosaurs, however, are all subject to criticism and error, as fossilization processes can change the geochemical data of fossilized bones, so it is necessary to search for alternative methods that give more accurate results.

Scientists also used histology by studying the growth rings in the bones of ancient animals, which resemble tree rings, and these rings indicate the years of growth in the organism, and by calculating the distances between them, it is possible to know whether this organism is fast-growing or it is growing slowly, and then This is measured on metabolic rates, as it is known that animals with a high metabolic rate have a rapid growth rate, unlike those with a low rate that grow slowly, but this method also has some inaccuracy, as the speed of growth or slowness can be on It has more to do with the animal’s age than its metabolic rate, and applying this method to access that information could damage the fossil.

Bones don’t lie

Since all the ancient methods are in doubt, scientists had to come up with new ways to explore the mysteries of these abyssal lives, and this is what the team behind this study found. They targeted one of the hallmarks of metabolism, which is the consumption of oxygen; When animals breathe, side compounds are formed that react with proteins, sugars and fats, leaving behind molecular “wastes”. metabolism.

Scientists searched for these bits of molecular waste in dark-colored bone fossils; Because these bones indicate that a lot of organic matter was preserved during the fossilization process, these bones were then examined using infrared spectroscopy of the Raman-Fourier transform, a method particularly attractive to paleontologists; Because it is not destructive to fossils, this spectrometer works to capture the signals of metabolic molecules in both the bones of living animals living today, as well as those that are extinct and fossilized by exposing them to laser light and nothing more, which allowed the researchers to study a large number of samples in a short time and without destroying them.

The use of these unique technologies was met with a standing ovation; The study was well received by many specialists in the study of dinosaurs. Gregory Erickson, a paleontologist at Florida State University, who is not involved in the research, told Al-Alam: “It is a very exciting study that opens new horizons for the future of vertebrate palaeontology to be an integrative science. More reliance on modern technology.

He added, “I think most researchers would agree that dinosaurs were warm-blooded. I’m not sure the public understands the implications. That’s simply the story. The results of the study showed that it was much more complicated. I think they’re right. The methods that this team used are impeccable.” Impurity, we scholars need to rethink this paradigm.

“I have always believed that studying extinct animals using living animals living today is commendable,” adds Erickson. “I think the findings of this study influence countless aspects of the study of dinosaurs and our understanding of bird evolution, indeed our understanding of animal energy, growth, and population biology.” reproduction, and other important topics.

Dinosaurs are like descendants of birds

The team studied 55 femurs collected from different animals, including dinosaurs, their flying cousins ​​(Pterosaurs) and their marine relatives, birds, mammals and modern reptiles. The data were used to infer the metabolic rates of extinct animals, and the team found that the dinosaurs’ metabolic rates were generally high.

Anatomically, dinosaurs are divided into two large families according to the shape of their pelvic bones: ornithischians (having pelvic bones that resemble birds) and lizards (having pelvic bones resembling reptiles).

Aquarium lizards, in turn, are divided into two large groups: theropods (all carnivorous dinosaurs) and sauropods (herbivorous dinosaurs).

Ornithological dinosaurs such as Triceratops, Stegosaurus, and Hadrosaurus had low metabolic rates similar to those of today’s cold-blooded animals, while pelvic lizards had a metabolic rate as high as their warm-blooded counterparts today.

The researchers were surprised when they discovered that some of these dinosaurs were not only warm-blooded, but their metabolic rates were similar to modern birds, and much higher than mammals, and it can be said that they were the animals that had the highest metabolic rate among all the extinct animals.

Higher metabolic rates in warm-blooded animals facilitate rapid growth, while lower metabolic rates in cold-blooded animals lead to relatively slower growth.

Here, “Weiman” adds: “Scientists have long believed that the great herbivorous dinosaurs of the sauropods were endothermic, or what is scientifically known as “gigantothermy,” which means that they had low metabolic rates to be able to control the temperature of their gigantic bodies. Our current study completely denies this, and proves that these organisms had one of the highest metabolic rates.”

As for Jimenji O’Canor – a paleontologist and curator of the Field Museum of Natural History in the United States, who is not involved in the research – she told Al-Salam: “These findings not only change what we can learn about extinct animals, but also change our understanding of their lifestyle. Knowing that some animals, such as the great sauropod dinosaurs, have elevated metabolic rates will change how we interpret their behavior and biology.”

Did metabolism contribute to the extinction of the dinosaurs?

In addition to giving us insight into the ancient lifestyle of dinosaurs, 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 a meteor struck Earth, and today ecologists tend to Emphasizing the importance of metabolic rate to ensure animals survive environmental disturbances, assuming that a high metabolic rate in general is one of the main advantages of surviving mass extinctions and successful dispersal thereafter, and some scientists have suggested that birds survived while non-avian dinosaurs died, due to the increased metabolic capacity of birds However, the current study denies all these claims and shows that this is not true; According to the results of that study, many dinosaurs became extinct even though they had bird-like metabolic rates.

Although this study answered several important questions that remained a mystery for a long time, it in turn opened the door to larger scientific questions and puzzles, which opens the door to the need for future studies to answer them.

In fact, if the results of this study are confirmed, it opens the door to a new scientific debate: when and why amniotes evolved (tetrapods that develop amniotes) She lays her eggs with an amniotic membrane, i.e. strong and yet transparent) The characteristic of warm blood for the first time? Why and how did aquarium finches “reverse” their metabolic rates? How, though, were they able to colonize high latitudes when warm-blooded sauropods did not?

Accordingly, dinosaurs and other extinct animals continue to gain the attention of the human mind, and the passion to unravel the mysteries of these abyssal animals, for a clearer understanding of the present and future of life on earth.