Like modern birds, T. rex and allosaurus were warm-blooded

Birds are warm-blooded, while lizards are cold-blooded. Both groups are related to dinosaurs. For this reason, paleontologists have long wondered whether these deniers had slow (cold-blooded) metabolisms like their lizard cousins ​​or high metabolisms like their avian relatives. Scientists now know the answer: both.

An animal’s metabolism refers to the amount of energy the body uses to function normally. An animal with a high metabolism is often more active, but it must compensate by eating enough food and breathing enough oxygen to keep the metabolic engine running. As a bonus, this high metabolism generates heatThus keeping the warmth of these animals.

The opposite metabolic strategy requires less energy. So these animals need less oxygen and food to develop. However, this metabolism process does not generate enough heat to keep them warm. So they must Regulating body temperature Lay in the sun or hide in the shade.

What about dinosaurs?

Today, only birds and mammals are warm-blooded, others are cold-blooded, but what about millions of years ago? As part of the study, a team led by JCalTech’s asmina Wiemann became interested in fifty-five speciesincluding many dinosaurs, with the goal of tracking the evolution of metabolism over time.

Previous studies have already addressed this question. However, this work had two main drawbacks. First, the researchers tended to infer metabolism indirectly by analyzing eggshell thickness, tooth structure, or isotopes left after fossilization (differences of an element with a different number of neutrons). These factors are often used to determine growth rate or body temperature which are indicators of metabolic rate. However, these measures remain indirect. On the other hand, the methods used to conduct this research are Often invasivewhile forcing researchers to destroy fossils to obtain their data.

For this new study published in Nature, researchers used a light scattering microscope To determine the chemical composition of bone. It is a non-surgical method. More specifically, they searched for Waste products of the same metabolism (such as hydrolyzed fat) which can indicate the use of oxygen in the animal’s body (a direct measure of the metabolic rate).

Microscopic view of soft tissue extracted from Allosaurus bones. Credits: J. Wiemann

Diverse and sophisticated metabolism

In the Triassic period, there Between 251.9 million and 201.3 million years agoDinosaurs were divided into two large groups with on the one hand the Saurischians (lizard-hipped dinosaurs) and on the other, Ornithischians (bird-hipped dinosaurs). The results of this work indicate that members of the first group, which notably includes the T-Rex and many other theropods, were warm-blooded. Birds of this line maintained a similar metabolism.

On the other hand, Ornithischians, which include ceratopsids (such as Triceratops) or hadrosaurids (duck-billed dinosaurs), lost their rapid metabolism over time and became cold-blooded animals. In the end, the dinosaurs had Various metabolisms that follow an evolutionary pattern.

Aside from dinosaurs, the study also reveals that warm-blooded metabolisms arose in two different evolutionary lineages: in mammals and a group of extinct marine reptiles known as plesiosaurs. Not only did these lines achieve higher metabolisms independently of each other, but they all did so at roughly the same time during Triassic period.

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