My family’s standard poodle smiles when any of us come home. Her smile consists of the bared teeth (but somehow looking subtly different from a snarling face), accompanied by snorting and much tail- and butt-wagging. Now she can do it on command too. Her mother did it as well, so maybe that’s how she learned it. Oddly enough, our previous poodle never smiled.
I have had two dogs that smile. One was a greyhound, and yes, he would smile at our other dog. Usually as part of an invitation to play.
CurrentDog smiles almost all the time except when he’s sleeping. He’s a Very Happy Dog. There is a difference between his smile and his “open-mouth breathing”, too - he has dimples when he smiles. Yes. Dimples. Honest. (No, I have no pics - sorry.)
Seeing the other responses from people, I have to wonder if it’s partly a “jowly” thing - Greys have startlingly large jowls (you wouldn’t think it from seeing them, but honestly, they have “chipmunk cheeks”). CurrentDog is part Lab, and has the jowls to match. My other two FormerDogs that did NOT smile weren’t at all “jowly”, so perhaps that does have something to do with it.
<shrug>
But then again, that’s a WAG and someone will no doubt be along shortly to prove me wrong.
jeevpup very definitely smiles. It’s a big open smile when he greets me at the door, and a grin with his teeth showing when he gets a tummy rub. He also does a thing with the skin above his eyes when he’s pleading that’s very adorable.
One my current greyhounds smiles. Here’s his pic:
http://www.unc.edu/~nbeach/idol01.htm
And our dear departed Rob Roy would as well.
Here’s another smiling greyhound:
http://www.compassionforgreyhounds.org/Wingie.htm
There’s a web page out there with a whole bunch of smilers, but unfortunately I can’t seem to dig it up.
When I worked part time as a pet-sitter, we took care of a Golden who would smile as well.
I’ve always thought it was a submissive gesture - if you’ve ever watched nature films about wolves and their behavior, you’ll see when the alpha pair come back from hunting, the other wolves will greet them with a number of submissive gestures - they’ll flatten their ears, walk lower to the ground with their tail low but wagging, smile, and even roll over and expose their bellies. Young wolves will also often lick the alpha’s lips. Our Idol will do many of these things in his greetings to us. I just consider him a bit less evolved than one normally finds in domestic dogs 
This used to happen to my dog Sasha. We called it a puppy sneer.
I knew a smiling dog in my youth. I haven’t seen one in ages though. My Bouncer dog does a sort of closed mouth smile. When you’re scratching his chest and he’s very happy, his eyes will squinch closed and the corners of his mouth will turn up a little. He’s a cutie.
I’ve been involved with field and ex-racing greyhounds for, um, longer than I care to think about. Smiling is fairly common in the breed, and tends to run in certain bloodlines. Most smile with their canines bared (which is what I assume the picture shows), and this behavior seems to have a storng genetic component. I’ve never noticed a smailer smile at another hound, but I’ll have to think about it.
A few, including a mother and daughter I currently own, smile with the back corners of their mouths. Both of these hounds are very imitative of humans, and each other, so I don’t know where this behavior originated. It definitely didn’t show up until they were fully mature.
The weirdest canine communicator I ever had was a Whippet who didn’t smile, but could, on occasion, purr very much like a cat. Where THAT came from, I have no idea.
Our Idol does this sometimes as well. He also makes a whole host of other sounds - by far our most vocal hound.
Selkie, have you ever shown or coursed your hounds in the Southeast? Perhaps I’ve met you or your pups.
Selkie
Purrs?!? Your whippet actually purrs? Jesus. I thought my Italian Greyhound was a weirdo.
Romansperson
I’ve got a picture of a smiling iggy somewhere around here. I’ll post it if I can find it. BTW I showed the picture of Rob Roy around the office. It cracked everybody up.
Our bull mastiff does, its hilarious to see. He has floppy drooly jaws and somehow manages to pull all that up and show his teeth, so he gets all these huge wrinkles along his nose and head. I guess it would be rather frightening though if you didn’t know it was a smile. The sad thing about it is that he refuses to smile for other people or for a camera… so very few people have ever seen it.
Labrat. Yes, purred like a cat. Soft purr, unlike the roar that emanates from my tiny little calico, but definitely a purr. Great way to freak out other whippet people who came to pet him.
romansperson, my coursing days are well past me, although I keep a hand in through my friend’s Afghans (kennel name Twyshire). It’s possible you would have heard of my greyhound Point Breeze California Girl LCM SC (Cally), who was the #3 ASFA greyhound around 1994ish (and, incidentally, is one of my smilers).
The whippet I mentioned, Prophecy’s Love Me Tender FCH (Elvis), although never a top competitor, had quite a wide ranging reputation. I’ll never forget driving to PA (from IL) at the last minute to squeeze in a few more Bowen points for Cally, and finding out that all the whippet people present, whom I’d never met, knew who he was by reputation. He won more on heart than ability, but he was legendary for his, um, “intensity” off the field and the stories that tended to accumulate around him. I once had to scratch him from a trial because he had eaten blue suede. The trial secretary swore I was putting her on until it started coming out of him. Given that, the purring, and his history before he came into my life, he was one of those characters whom far more people knew about than his skill on the field would have otherwise justified. Even in death, the stories continue. Both family and friends who visit the house hear him stepping in and out of his crate, even though the crate is long gone and so is the whippet who called it home. The other hounds still leave his place on my bed empty, and it’s often warm. (Insert your own “Elvis lives” joke here, if you must). I miss him fiercely.
My chow/lab mix does this when he’s really happy, excited or about to get a treat. He gets so excited that he bounces up and down and his tail is going in a circle like a helicopter rotor.
My chow/lab mix does this when he’s really happy, excited or about to get a treat. He gets so excited that he bounces up and down and his tail is going in a circle like a helicopter rotor.