Now, with the Pie family, it's quite obviously Pie. With the Cake family, it's Cake. But with the Apple family, it just seems to be nonexistent. And most people say that, for example, that Rarity is "Rarity Belle."
Shining and Twilight don't share a last name. I think her parents don't either, I think her mom shares her FIRST name, like quite a few of the apple family.

So...
There are no surnames? Just freakin names?

991620
No idea, but I like to add a surname every now and then.

I have two names that really don't have a last, but I created some that more or less fits their personalities.

(Not sayin what they are because SPOILERS for my story. Also I don't want them stolen.)

991620
Just freakin' names. Maybe ponies aren't as hung up on lineage as humans are because they're a matriarchal society?

Yes. They just have freaking names. They can choose to pass on something of a surname if they want, but they don't have to.

It may be a tradition with some families and not others. In a story I'd just go with whatever works for you.

991684 Is that information canon? If so where can I read it?

991656 This wasn't for a story, I just thought of it today and got a little angry when there was no answer.

991684 My head hurts

991620
The idea of ponies with surnames really annoys me. Ponies obviously don't follow traditional western naming conventions, and it pisses me off when people try to combine the two.

I am unsure how naming conventions work exactly, but my current headcanon is that it is a little like cutie marks—when they are born, their parents instinctively know what to call their child. Sometimes this results in theme naming, like the Cakes, or the Apples. Sometimes you get wildly different names, like Twilight Sparkle and Shining Armour. And sometimes you get ponies with just one name, like Rarity. The one consistant in all their names is that it sounds aesthetically pleasing. "Rarity Belle" doesn't. It is forced, ugly and fails to flow off the tounge.

And even if you did use surnames, how would that work? Would you take the stallion's name, or the mare's? Equestria is a mare dominated, matriarchal society (because horses). So if you took the mares name, then in Twilight's family we would have Twilight Velvet, Nightlight Velvet, Shining Armour Velvet and Twilight Sparkle Velvet—all very clumsy on the tongue. I don't even know how it would work with stallion names, seeing as Nightlight only has the one name—something that's refered to as a monomym, a characteristic present in many real life cultures (assuming that's even his name—Nightlight is a female G1 pony he just happens to look like, and Twilight Velvet looks like the G1 pony Twilight, also known as Galaxy. So we can't even use traditional western naming standards here even if we wanted to, due to lack of information.)

Now onto the headcanony bit. In order to bind together family units under a common banner (like surnames do in the western world, or the clan and family name in roman culture, both of which were heridtory, or the uppername in japanese culture), ponies are arranged into "houses" "clans" and "tribes", depending on their social status. Pinkie and Applejack, being farm labourers, come from clans (the Apple, and persumily the Pie, if we extrapolate from the references to a 'Granny Pie'. Although, why would a family called "Pie" work on a rock farm in a world where your name is supposed be a descriptor?). I see Rainbow Dash and Fluttershy coming from a more militant minded tribe (the same one in my headcanon, Clan Huricane, although there are so many degrees of separation between the two they can hardly be called related). Dash embraces this military heritage (martial arts, joining the Wonderbolts) whilst Fluttershy rejects it.
Alternatively, Fluttershy comes from a noble house, explaining her gentle nature and freaky knowledge of sewing. Twilight also comes from a house, although it is a weak house despite the prominent positions of Twilight and Shining. Rarity, being a commoner, is houseless, and her family unit consists of herself, her parents and Sweetie Belle, whilst everypony else has the wider clan/tribe/house structure to fall back on.

So yeah, I don't believe in giving ponies surnames. It is trying to impose western culture onto an unrelated fantasy culture, and is highly arrogant, as if the western naming convention is the only naming convention, when in reality it is simply the most common form of naming at this time on this planet, with many cultures (mainly Eastern European, Asian and African) using their own, personal variations.

991620
Surnames are a farely new concept in this world (even among nobility), mostly for rulers to categorize their subjects for tax reasons.

Proof of concept, how many Greeks can you name by their 'full name'? Sokrates, Plato, Pythagoras, Aristophanes...All of them simply had only a given name.

991620
Well, clearly there's certain family groups or clans that follow the whole surname tradition.
You point them out. Apples, Cakes, Pies. All earth pony families dealing with food.

Also just as clear, most ponies don't use surnames.

Seems to me like it's just a sort of fringe tradition among earth ponies, which the rest of Equestria doesn't follow.

It's possible extended family or bloodlines aren't that important. Or that what clan/family/herd/whatever that you belong to just doesn't get used when introducing yourself, so that Shining Armor, say, might have a birth certificate with his name, and his filial herd/clan on a separate line, which isn't really used for much but official purposes.

from hat i understand ponies share similar cutie-marks with there family's for example Shining Armour's shield has the same star as twilight and the apples all have...apples

993319 but Pinkie has balloons.

992658
It seems that some of the ponies follow the old Viking tradition, where the child has a name derived from the coresponding gender parent.
Ie. Eric's son = Ericsson (that is the last name of the male child)
Inga's dauter = Ingasdauter (the daughter's last name, an bad example, it's after 11p.m. where I am)