An international team of researchers has re-examined the origins of warm-bloodedness by analyzing deceased amniote ancestors. The authors studied small erythrocytes, a feature of endothermic organisms that has not been considered before.

The ability of living things to produce internal heat for the entire organism is called endothermy, and in everyday life it is called warm-blooded (although it is not strictly the same thing). All mammals and birds, as well as the red-haired opah (a type of fish).Lampris guttatus). Dinosaurs and their ancestors had the same ability.

For decades, the scientific community has been trying to figure out where warm-bloodedness comes from in amniotes (treasures of quadrupeds with embryonic membranes): is this trait acquired or inherited? In 2021, a group of biologists led by Gordon Grigg (Gordon Grigg) studied the first versions of the origin of warm-bloodedness and noted that endothermy appeared in amniotes even before the division into synapsids (ancestors of mammals) and sauropsis (ancestors of reptiles). dinosaurs). In other words, according to the authors, the history of warm-bloodedness is more than 300 million years old. Naked Science talked about this in more detail.

But recently another international team revisited the issue. The authors reviewed the group’s Gordon Grigg version and noted that historical data did not take into account early amniotes, which are now extinct species. Based on additional analysis of the thermophysiology of these animals, the researchers suggested that endothermy may be an acquired quality of amniotes. Preliminary versions of articles are published on the journal’s website. iScience.

One of the signs by which you can determine whether the body can or cannot maintain a high body temperature is the size of the erythrocytes. According to one review, the development of smaller blood cells with higher specific surface area, along with other changes in the circulatory system, was a critical factor in endothermy; because small red blood cells accelerate the delivery of oxygen to the cells. With the decrease in erythrocytes, the blood vessels also decreased. Researchers examined the aerobic capacity and thermophysiology of extinct amniotes based on the diameter of blood vessels in the bones; this is indirect evidence of the size of the blood cells.

The warm-blooded system is complex and incorporates many features. The authors state that this mechanism will not work effectively if some important parts are missing. Tiny erythrocytes, an important component of the endothermic system, are absent in early amniotes, according to the study.

Scientists evaluated, among others, an extinct species of tetrapodomorph whatcheeriaIt was considered a warm-blooded predator. Analysis of the diameter of its vessels showed that it belonged to ectothermic organisms. The authors say that the cardiovascular system whatcheeria and other ancestors of amniotes did not develop the efficient tachymetabolism characteristic of warm-blooded organisms.

However, researchers emphasize that analysis of the size of red blood cells is not the most accurate assessment method. Therefore, such an approach to investigating the origin of endothermy should be approached with caution and all ancestral forms of amniotes should be taken into account.