Did noses evolve for smelling or for breathing?

[Speaker for the Dead]

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?

[Colibri]

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 (http://www.newscientist.com/article/dn6607-fish-fossil-confirms-origin-of-nostrils.html) appears to confirm an intermediate stage in this migration.

[Leo Bloom]

Colibri, who knew you knew so much about nostrils?

[Blake]

Colibri, who knew you knew so much about nostrils?

He nose his stuff.

[panache45]

That's nothing to sneeze at.

[Peter Morris]

He makes a lot of scents.

[Sunspace]

These puns stink.

[Peter Morris]

Okay, from now on, puns are strictly No-Nos.

[Polycarp]

If you ever figure out how to avoid 'em, sinus up!

[Colibri]

Colibri, who knew you knew so much about nostrils?

C'mon, I've always been a nose-it-all.:)

[Gary T]

If you ever figure out how to avoid 'em, sinus up!
What's to figure out? It's as plain as the....oh, never mind

[Toucanna]

Great question and love the puns, just one clarification: not all species of mammals can breathe through their mouths. Horses are one example.

[WhyNot]

Great question and love the puns, just one clarification: not all species of mammals can breathe through their mouths. Horses are one example.

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.)

[psychonaut]

Great question and love the puns, just one clarification: not all species of mammals can breathe through their mouths. Horses are one example.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?

[WhyNot]

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:

[Gorsnak]

Noses evolved for making more babies, same as everything else. :p

[enalzi]

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 (http://www.newscientist.com/article/dn6607-fish-fossil-confirms-origin-of-nostrils.html) appears to confirm an intermediate stage in this migration.

Interesting. When I saw the question, I immediate thought, "it had to be breathing, otherwise why would air be drawn in." Ignorance fought!

[Colibri]

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?

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. (http://en.wikipedia.org/wiki/Obligate_nasal_breathing) 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.

[GiantRat]

Y'all may think your pun is funny, but it's not.

[Siam Sam]

So what's up with those two lines that come down from the nose?

[don't ask]

And here I was thinking that the nose evolved to facilitate modern office politics.

[JKellyMap]

So what's up with those two lines that come down from the nose?

Ask Phil somebody (http://www.google.com/imgres?imgurl=http://www.hahastop.com/pictures/Philtrum.jpg&imgrefurl=http://www.hahastop.com/pictures/Philtrum.htm&h=560&w=600&sz=53&tbnid=o3rRqOeWIsi2jM:&tbnh=90&tbnw=96&prev=/search%3Fq%3Dphiltrum%26tbm%3Disch%26tbo%3Du&zoom=1&q=philtrum&docid=CqZDCCZm7F-ClM&hl=en&sa=X&ei=h65JT-7SLpGctweZt-DxAg&sqi=2&ved=0CEgQ9QEwBg). He nose.

[phreesh]

Somewhat related, but why are the nostrils downward pointing? In the great apes, the nostrils are forward facing, which seems like the more 'natural' way for them to be utilized for the intake of oxygen and odors.

I've read that it's to facilitate swimming, so water doesn't [easily] get into your nose, but that seems pretty far-fetched. Is there a factual answer to this?

[Speaker for the Dead]

Guys, wow. I haven't been on the SDMB for months and months, and my first thread nets me BOTH the answer I want and an amazing series of puns. I'm sad I ever left!

[Zebra]

Moses supposes horse noses are hoses, but Moses supposes erroneously.

[Autolycus]

What selective pressure caused it to be lost in horses, do we know?

Sinus pressure?

Or what Colibri said. One of the two!

[Elendil's Heir]

These puns stink.

Then why'd you come sniffing around here?

[Chefguy]

Then why'd you come sniffing around here?

He's nose it adenoids us.

[Tom Tildrum]

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.

And yet they never discovered oral sex....

[psychonaut]

And yet they never discovered oral sex....On the contrary… (http://www.metro.co.uk/weird/1427-gay-dolphins)