paleontology. By studying the hearing channels of hundreds of species, living and extinct, an international team has turned upside down the calendar and the speed of appearance of endothermal animals.
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Stefan Glasauer thought not to ignore much of the secrets of the inner ear. Professor at the Technological Institute and the Medicine School of the University of Brandenburg, Germany, he dissects the auditory but above all positional role of this curious labyrinth. Perceive the angular movements of the head, record the acceleration of the body, adapt the vision, keep balance … “It has been years since I work on this vestibular system. Discover today that the dimension of the sensors could inform us about the temperature of extinct species, I admit that it impresses me, “he confides.
An international team bringing together scientists from seven European and American countries published on Wednesday July 20, in the journal Nature, an article offering a new chronology of an essential step in animal evolution: the appearance of so -called species “Hot blood”. “Until then, the animals were all Ecototherms. Their temperature depended on that of the outside, underlines Ricardo Araujo, researcher at the University of Lisbon and the first author of the study. It is the acquisition of endothermalia which allowed mammals and birds to explore different climates, to go out in all seasons, day and night, to move faster and longer. All the innovations attributed to our humanity also depend on this moment- There. “
” a brilliant idea “
To track down this rocking, scientists have, for several decades, multiplied approaches. Analyze posture, diaphragm, nasals, dentition, chemical isotopes in the bones … “The results were often contradictory and unconvincing, estimates Romain David, postdocho at the London Natural History Museum and co-prime author of the Research. But the main hypothesis wanted this transition to take place around 255 million years ago in a gradual way. “
It is to try to verify the relevance that in 2017 Araujo and David decided to look into the inner ear. “Our reasoning was quite simple, says the French of London. The semi-circular channels of the inner ear are sensors traveled by a fluid, the lymph. When the temperature increases, it is as with honey, the viscosity of the Fluid decreases, so the eyelashes that record the information capture it less well. However, we have known for more than fifty years that the mammals’ channels are proportionally smaller than those of lizards or fish. We have hypothesized that, for Compensate for the loss of efficiency, they had evolved by reducing the size of the tubes. “” Linking viscosity of the endolymph, body temperature and canal morphology is really a brilliant idea, comments Guillaume Billet, lecturer in paleontology at Museum National of Natural History of Paris. And they demonstrated it by integrating several scientific fields: mechanics of fluids, physiology, morphology and evolutionary biology. A particularly substantial dataset. It is very impressive. “
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