The timing of this transition, to an essential feature of mammals, remains a matter of debate. They would have become endothermic, that is to say warm-blooded, and no longer cold-blooded as reptiles remained, around 252 million years ago. At the time of one of the great extinctions of species, in the Permian.
The problem is you can’t just put a thermometer in a fossil, you can’t know its body temperature.says Ricardo Araujo, from the University of Lisbon, one of the authors of the study published in Nature.
The researchers got around the problem by examining the semicircular canals of the inner ear fossils of 56 species of extinct mammals.
The inner ear, which is used to maintain balance, is traversed by a fluid, which the researchers found that the temperature rose in concert with that of the animal’s body. With the consequence of making this fluid more liquid.
Ricardo Araujo illustrates this by comparing it to the oil in a fryer,
very viscous and very dense before being heated, and which after
flows much more easilyhe told AFP.
In the case of the inner ear, this fluidity has led to finer semicircular canals, whose size evolution according to that of the body has been modelled. With the conclusion that the transition to a warm-blooded system occurred 233 million years ago.
A model that works for all mammals, including humans, that
lets look at your inner ear and tell you how warm blooded you areexplains to AFP the main author of the study, Romain David, of the Natural History Museum in London.
appears to work well for a wide range of contemporary vertebratessays Michael Benton, a paleontologist from the University of Bristol, who was not involved in the study.
It does not simply provide a yes/no answer, but determines the “degree” of endothermy in terms of baseline body temperaturehe said to AFP.
Mr Benton, whose research had previously determined the appearance of warm-blooded mammals 252 million years ago, says this transition happened in stages. With some
significant progress preceding the change in architecture of the inner ear.
On the other hand, for Mr. Araujo, the transition to a warm-blooded system came
very quickly in geological terms, less than a million yearshe argues, excluding
a slow, gradual process over tens of millions of years, as previously thought.
Another argument against a transition 252 million years ago is that the very high temperatures at that time, around 31 degrees Celsius, would not have provided an advantage to warm-blooded animals. On the other hand, they would have benefited from the drop in temperatures that followed, over millions of years.
Being an endotherm makes it easier to overcome climatic hazards, to run faster, longer, to explore new habitats, to explore the night and the polar regions, to make long migrationsaccording to Mr. Araujo.
So many things that have shaped what a mammal is
and also, ultimately, what a human being would be likesummarizes the researcher.