Scientifically speaking, there is no evidence that proves animals can smile. It's possible that what we think of as animals smiling may just be a case of pareidolia, a psychological phenomenon where we see human faces on animals and inanimate objects.
Animals are still quite emotive so just because science can't prove their ability to smile, it doesn't mean that they can't feel joy.
Frankly there are very few things in the world that can make you as happy as looking at adorable photos of animals with smiles on their faces. Here are 20 of the smiliest animal photos that'll lift your spirits and put a smile on your face too: