Dinosaurs were still warm-blooded

(ORDO NEWS) — For a long time, paleontologists debated whether dinosaurs were cold-blooded, like modern reptiles, or warm-blooded, like birds and mammals. Now, the issue seems to be resolved: many dinosaurs maintained a constant body temperature – the evidence is the remnants of biological molecules in their bones.

Over the past decades, our understanding of dinosaurs has changed a lot. They no longer seem purely primitive and cold-blooded “killing machines” in every sense.

On the contrary, many had colorful plumage and complex social interactions. The next blow to the “myth of toxic reptiles” of the ancient lizards was the finally resolved issue of their warm-bloodedness.

An important evolutionary invention of vertebrates was the so-called homoiothermia (warm-bloodedness, endothermia) – the ability to maintain a constant temperature due to metabolic processes.

Warm-bloodedness is not similar to such evolutionary breakthroughs as, say, the spine or intestines, which first appeared in the most ancient vertebrates and were subsequently inherited “with changes and additions”.

The ability to actively generate heat appeared independently in mammals and birds – it is difficult to say exactly how many times in the history of the biosphere. Moreover, avian warm-bloodedness is considered more effective and originated among the ancient and primitive representatives of this branch of evolution.

Homeothermic animals are opposed to poikilothermic (cold-blooded, ectothermic). They are unable to generate heat with their metabolism, although they are sometimes able to obtain it in some other way – say, by actively working their muscles, basking in the sun, or even “stealing” it from others. Cold-blooded include various fish, amphibians and modern reptiles – crocodiles, turtles, tuatara, lizards and snakes.

Dinosaurs were still warm blooded
Reconstruction of the evolution of the considered species, warm colors show a high metabolic rate (high “degree of warm-bloodedness”)

Many considered poikilothermic and dinosaurs – “terrible lizards”, which, together with sea and flying lizards, dominated the Mesozoic era. Indeed, why should they waste resources on maintaining a constant temperature during that warm and even hot time? On the other hand, warm-bloodedness is not only a certain temperature, but also a fast metabolism and better adaptation.

Now, however, disagreements on this score should be in the past – at least, so the authors of a new article in Nature believe. A team of scientists led by Jasmina Wiemann from Yale University (USA) studied the remains of biological molecules from many dinosaurs.

“A new protocol developed by Jasmina Wiemann has allowed us to directly examine the metabolism of extinct organisms, something we could only have dreamed of a few years ago.

We also found that different groups had different metabolic rates, which had previously been suggested based on other methods, but there were no direct tests yet, ”said Matteo Fabbri (Mattheo Fabbri), co-author of the new paper.

Since metabolism is primarily the efficient use of oxygen and energy, researchers have been looking for molecules that can estimate the rate of these processes.

The objects of study were 55 species of animals, including many dinosaurs, their flying relatives pterodactyls, marine plesiosaurs, as well as a number of modern terrestrial vertebrates (amniotes).

In samples of the femurs of all these animals, spectroscopy revealed traces of lipid oxidation and various “crosslinks” of biomolecules, which correlate well with metabolic activity. This made it possible to confidently judge who could maintain body temperature at a constant level, and for whom it depended on the environment.

Paleontologists have graphically depicted this as an evolutionary tree, where there are separate “warm-blooded” branches and it is clear that they arose independently.

The main conclusion lies precisely in the warm-bloodedness of plesiosaurs and pterosaurs, as well as dinosaurs such as velociraptor, tyrannosaurus or brachiosaurus, that is, a group of lizards. Many of them had not just warm, but “hot” blood, that is, the metabolism is faster than that of modern birds.

At the same time, representatives of another large group of predominantly herbivorous dinosaurs (Ornithischians) like Triceratops and Stegosaurus were quite cold-blooded.

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