Warm - blooded tyrannosaurs
Many dinosaurs were most likely warm-blooded
Yulia Panchenko, PCR.news
For several decades, scientists have been debating whether dinosaurs were warm-blooded, like birds, or cold-blooded, like reptiles. Knowing this, you can make predictions about their behavior and activity level. Isotopic geochemistry has not given an unambiguous answer, because scientists do not know enough about the process of formation of fossils, nor has the analysis of growth lines made it clear. In a new paper, researchers from the United States studied the metabolic rate of dinosaurs and birds — the volume of oxygen inhaled per hour per gram of body weight. They used Raman and infrared spectroscopy with Fourier transform to analyze accumulations of lipid oxidation products. These methods also have the advantage that they do not damage the sample. A high metabolic rate indicates probable warm—bloodedness, a low one indicates ectothermy, or cold-bloodedness.
Soft tissues from allosaurus bone. Credit: J. Wiemann.
Heat is a byproduct of the breakdown of fats and sugars. The resulting chemical energy is involved in the formation of adenosine triphosphates during oxidative phosphorylation in the outer membrane of the mitochondria. During oxidative phosphorylation, ROS are formed, which penetrate the mitochondrial membrane, interact with lipids and form reactive carbonyl compounds. These compounds react with amino acids of cellular and extracellular proteins. This cascade of oxidative reactions is known as "metabolic stress". As a result, the final products of lipoxidation (CPL) are formed — N-, O- and S-heterocycles and (thio)esters. The authors tested the hypothesis that CPL can be detected in fossils.
The analysis used dark—colored femurs, which means that a lot of organic matter has been preserved in the fossil. The authors studied the remains of dinosaurs, pterosaurs, plesiosaurs, as well as modern mammals, birds and lizards. The signals that come from the CPL were used as metabolic markers. Comparing the amounts of CPL with the known metabolic rate of modern animals, the authors estimated the metabolic rate of extinct animals.
Dinosaurs often had a high metabolic rate. But the avian, for example, Triceratops and Stegosaurus, had a low metabolic rate comparable to modern cold-blooded. The lizard-like Velociraptor, Tyrannosaurus rex and Brachiosaurus were most likely warm-blooded. Some dinosaurs had a metabolic rate comparable to that of birds, which was surprising to researchers.
Jasmina Wiemann, a molecular paleobiologist at Yale University and the first author of the study, makes assumptions about the behavior of dinosaurs based on new data. From the low-metabolic rate birds, one could expect "behavioral" thermoregulation, like in lizards and turtles that bask in the sun. They may also have migrated to warmer terrain during the cold seasons. Warm-blooded dinosaurs could be more mobile. Herbivorous giant sauropods would have to consume large amounts of food to maintain a high metabolism, and their digestive system would have to be very efficient. Because of their size, cooling was a bigger problem for them than heating the body.
Article by Wiemann et al. Fossil biomolecules reveal an avian metabolism in the ancestral dinosaur published in the journal Nature.
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