Background: I’ve taken the intro-level university paleontology classes, but they don’t cover the burning questions like “what were noses originally for?”
So, currently mammals can breath through their noses or through their mouths, which is a little redundant, and a lot of lower animals get by fine without noses at all. That’s what got me wondering: can we tell from the fossil record/current biology whether noses were initially developed as air passages (e.g. breathing while eating, breathing with most of an animal submerged, making sounds) or as passages to get air flowing by olfactory nerves?
Nostrils were originally purely for smelling. Fish have two nostrils on either side of the nose that open into a blind sac, unconnected to the mouth, that contains odor receptors. Water enters through one nostril and then leaves through the other.
Apparently at some point one pair of nostrils migrated inside the mouth where they became the internal nostrils (choanae) that permit air to be taken into the lungs. A recent fossil appears to confirm an intermediate stage in this migration.
I did know that. So, Mr. Nose-it-all (;)) How does that happen? If there was something after-the-fish split off that developed internal nostrils, how come not all mammals have internal nostrils? Did some proto-horse have them and then lose them, so modern horses don’t have them?
It seems like since so many mammals can breathe through their noses, for at least most of their lifespan, that it would have had to be a long time ago that it developed. What selective pressure caused it to be lost in horses, do we know?
(I know this is a thoroughly garbled post with flagrant mis-uses of evolutionary terms, but I hope you get the gist of what I’m asking.)
Breathing, as I understand it, involves moving air into and out of the lungs—i.e., inhaling and exhaling. When it comes to mouth breathing, horses clearly have no trouble with the latter, as anyone who has heard them vocalize can attest. So what’s preventing them from inhaling?
I just realized post 13 is moronic and I’m a drooling idiot. So sorry. Please ignore me today. I’d blame it on the cold medicine, only I’m not taking any. :smack:
Horses have internal nostrils like other mammals. However, they have an unusually tight seal between the epiglottis and soft palate that blocks off the pharynx (entrance to lungs) when they are not swallowing. Horses, rabbits, and rodents are regarded as obligate nasal breathers. Whales, for obvious reasons, have developed a separation between the respiratory and digestive systems in order to permit them to breathe and swallow at the same time.
