Our ancestors had two nostrils, one front and one back, but no opening on the palate or in the throat. They could smell, but not breathe with their nose. How did our nose evolve? Per Ahlberg, Uppsala university, and Zhu Min, department of Vertebrate Paleontology in Beijing, China, has now found a fossil that explains the history of the nose.
Have you ever wondered, taking a deep breath of fresh autumn air and sensing how the smell of wet leaves tickles your nose, just how it came about that you can do so? We humans take it for granted that our nose forms a passage between the world around us and our windpipe, but this hasn’t always been the case. We land-based vertebrates or “tetrapods” (mammals, birds, reptiles, and amphibians) originally descend from fish, and fish cant breathe through their nose. On the side of a fish’s head there are two nostrils, one front and one back, that form the opening to a little sac containing the olfactory organs: water flows in through the front nostril and out through the back one, but there is no connection whatsoever to the throat. In other words, fish can smell with their nose, but not breathe.
We tetrapods may have only one external nostril on each side of our head, but we do have an inner nostril or “choana” that opens on the palate or in the throat. This is what makes it possible for us to breathe through our nose. But how did this inner nostril evolve? One thing all scientists agree about is that the front nostril in fish corresponds to our single outer nostril: the question is whether the back nostril was transformed into our choana by “migrating” to the palate, or whether the choana is a new opening that arose with tetrapods.
Anneli Waara | alfa
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