(ORDO NEWS) — An international team of scientists analyzed the structure of the semicircular canals of the inner ear of mammals and their ancestors. This allowed them to understand at what point in evolution mammals became warm-blooded.
Scientists were able to determine when mammals became warm-blooded by the structure of their ears
An international team of paleontologists has found that the ancestors of mammals became warm-blooded about 233 million years ago, several tens of millions of years after their appearance in the mid-Triassic period.
How the study was conducted
Until now, scientists could not say when the first mammals became warm-blooded, and whether their ancestors from among the cynodont animal lizards (the oldest mammals) had this ability.
However, the results of a new study published in the journal Nature suggest that ancient mammals acquired warm-bloodedness about 233 million years ago.
To obtain these results, the scientists studied the structure of the ear bones of putative mammalian ancestors in 341 animals that lived on Earth approximately 235-220 million years ago, in the mid-Triassic period, as well as in 243 species of modern animals and 64 extinct ones.
As scientists explain, the bones of the inner ear contain a set of semicircular canals, which are necessary for the functioning of the vestibular apparatus. The semicircular canals are filled with fluid – endolymph.
Receptors of the semicircular canals respond to endolymph vibrations caused by head turns. This is necessary to maintain balance, perception of space and coordination of movements.
Thanks to the properties of endolymph, scientists were able to determine the occurrence of warm-bloodedness. The thing is that the viscosity of the endolymph depends on the temperature of the animal’s body.
The transition to warm-bloodedness would reduce the viscosity of the endolymph, which would negatively affect the performance of the semicircular canals. Therefore, the semicircular canals of warm-blooded animals must have undergone some changes in order to perform their functions effectively.
Guided by this idea, experts studied the ear bones of 56 species of ancient animal lizards, which were presumably related to our immediate ancestors. An analysis of their anatomy indicated that the ancestors of mammals became warm-blooded about 230-233 million years ago, but they acquired this ability in less than a million years.
The rapid development of warm-bloodedness in this era, as scientists suggest, was due to the fact that at about the same time the ancestors of mammals developed wool, whiskers and a special anatomy of the spine, which allowed them to actively move.
Subsequent searches for the remains of the last cynodonts and the first mammals, as scientists hope, will give a more accurate answer to the question of what caused the development of warm-bloodedness.
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