I 've kept all sorts of creatures over my life, as well as having been a keeper at two zoos, and I'd think most people might well be surprised at just how many different types of animals display what can(only) be described as emotions. It's hardly limited to the "upper primates". These can be seen in a lot of mammals, birds, reptiles and fish. I'd doubt it skips amphibians, it's just I haven't personally seen such displays nor read of them, and That certainly does t mean they dont have them too.
For example, chameleons don't change color so much to camouflage themselves(though their base colors do tend to blend in) their more vibrant displays of colors depend on their emotional state. They have combat colors, "Hey baby, hey baby!" Colors, " leave me alone" colors, and more.
In a sense I'd think it akin to degrees of consciousness. For centuries most animals were thought to be acting solely by instinct.
But any creature that learns from interacting with its environment has some degree of conscious awareness, just like the first cowboy to try eating a cactus, if it lives through it it learns. Similarly, you can bet that first cowboy HATES cactus, and therein is the start of emotion. It seems to me that the more socially interactive a species is, the more likely it is to have a wider range of emotive response, but that could just be the bias of a social creature.
It might just be me, but humans have been trying to differentiate themselves from The Animals for a long long time, and it seems like we jump on any unprovable(at the time)qualifiers at hand, you know, like how animals arent consciously aware, self determined, able to learn, capable of abstraction, don't feel pain, don't have emotion, don't have a soul, aren t made in gods image, can't use language, and more. Is it some deep seated insecurity that we might not be special? Guilt over that whole "dominion over" thing or some need to justify the claim? Or are we afraid that we're "just another monkey" ? This whole do our closest relatives have similar emotions to our own strikes me as a rather ridiculous question. Anyone who's spent any time observing them. knows they do, unless they approach it with the preconception that it's impossible, thereby giving excuse to ignore elements of what they see before them.