Tyrannosaurus rex and its relatives were warm-blooded, like modern birds

Birds keep warm through their active metabolism, and lizards rely on the Sun. Both of these groups

animals are related to dinosaurs.Because of this, paleontologists have long wondered whether these inhabitants of ancient Earth had a cold-blooded metabolism, like their lizard cousins, or a warm-blooded one, like their avian relatives. Now scientists know the answer: both.

A high metabolism generates heat, whichwarms animals, hence the term warm-blooded or endothermic. Otherwise, less energy is required to maintain life. This type of metabolism is known as cold-blooded or ectothermic metabolism. Such animals require less oxygen and food than endothermic creatures, but they must regulate their body temperature by lifestyle. Instead of generating their own heat, they maintain their internal temperature by basking in the sun or hiding in the shade.

The composition of dinosaur bones was studied by the authorsusing Raman infrared spectroscopy and Fourier transform infrared spectroscopy. The scientists analyzed the femurs of 55 different groups of animals, including dinosaurs, their flying relatives pterosaurs, their more distant marine relatives plesiosaurs, as well as modern birds, mammals and lizards. Paleontologists compared the amount of molecular by-products associated with respiration in modern animals with known metabolic rates and used the data to infer the metabolic rate of ancient animals.

Researchers have discovered that dinosaursdescended from a common ancestor, they were probably warm-blooded, but not all remained so. During the Triassic period, between 251.9 million and 201.3 million years ago, they split into two main groups: saurischian and ornithischian dinosaurs. Existing Evidence suggests that saurians, including carnivorous theropods such as Tyrannosaurus and Allosaurus, were warm-blooded creatures like their ancestors. 

Representatives of another group - ornithischiansdinosaurs, which included theropods and sauropods, turned out to be warm-blooded. Moreover, some of them had a metabolic rate comparable to modern birds and much higher than that of mammals. Theropod dinosaurs, a group that includes birds, developed high metabolisms even before some of their members could fly.

The authors of the work note that birds are the onlya group of dinosaurs that survived the mass extinction at the end of the Cretaceous period (approximately 145–66 million years ago), so perhaps their highly active metabolism gave them an advantage. However, this question remains to be clarified.

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