I have seen every MLP episode, short, and movie from every gen, and I have read a lot of the from every gen comics. Not all that is true but most, and that brings to my talking a point. That there are some equines that have never made into MLP canon, and I feel that is a shame. So that why I'm going to bring these over look equine to light for the fan writers in the hope that at least the fans talk about what it would be like to see these equine right beside the ponies. Now before I list these I want to make it clear I'm only listing common names of these species and only those that names are one word. This is because Hasbro will never scientific names and because while there are many different species zebra lets face facts Hasbro will never going details like that.

Tarpan: Equus ferus ferus also known as Eurasian Wild Horse is an sadly extinct specie of will wild horse. Now it the real world tarpans when it came to looks won't that different from domesticate horse and if they do become canon they probably won't look that different from the large horses like Trouble Shoes. This may seem like a big reason why they wouldn't become canon since they would just be big earth ponies, that is until you realize something. In G1 they would often so full sizes horses that won't the same things as ponies, some they would even so normal animals horses. G4 have done this a little so showings a lot bigger the normal ponies but aren't alicorns. That where the tarpans can come in, they can be the full size normal horse race without magical abilities or cutie marks.

Quagga: Equus quagga quagga is a now extinct specie best know for the fact it didn't look like most zebra species. Now because they look different from other zebra they could easily just be added in as another race of equine no problem.

Onager: Equus hemionus also known as hemione or Asiatic Wild Ass is specie closely related to donkeys. They do look different enough that even with cartoon looks added on they can be different enough in looks from donkeys to be their own race. Now what is need about onagers is that they are one of the fastest known land mammal species so there is some type of magic ability they could be giving right there. Increase their speed and make them more less ground Rainbow Dash in ability.

Kiang: Equus kiang the biggest of the species in the subgenus Asinus or asses if you will. It is also widely they were at least one of inspiration for the myth of the unicorn. So there is something right there in giving some kind of spell casting ability, now they do look a bit like the onager so that could be a problem in design.

Zebroids of all kinds: As you may or may not know all equine can interbreed with each to make hybrids. Mow most of these hybrids are called mules, unless one parent is a zebra. Then they are giving a name base on what their parents are but all collectedly zebroids. Now zebras get a long just fine with all equine species so if you leave a zebra with a non-zebra equine of the different you are going to get one of these sooner or later.

More lore is always fun I guess, but it might be difficult making interesting cultures for all of these, as well as coming up with unique designs. Would you give them individual kingdoms or towns, or have them living here and there in Equestria, like donkeys and mules? Or is there a far away donkey kingdom we never see? Or how about the bat ponies? I don’t think the crossbreeds would need to segregate themselves from wherever they came from, unless there was some ugly history going on.

I had an idea for a story I probably won’t write for awhile, where Fluttershy and Twilight investigate a long lost continent filled with, for lack of a better term, primal or archaic equines. I call them Caspians, because of this weird coincidence:

Caspians - the ancient people
Caspians - the ancient horses

In my version, Capians would be a living fossil descended from the common ancestor of all equines, about the size of the Saddle Arabians. They would exhibit, depending on the individual, pastel colors, stripes, spots, and other peculiar designs. They do not farm or live in cities, and instead wander and graze across a huge plain and visit various forests as the weather changes. They can’t talk outside of a range of chitters, neighs, and chirps, although Fluttershy can somewhat understand them, given her empathic abilities. They have a spark of intelligence in them, doing things like using gourds to haul water, decorating their manes with flowers, painting rock walls with natural paint dyes, and other symbolic gestures. They’re in a hazy gray zone between animals and sapients.

One current in the story would be Fluttershy starts thinking this is actually a superior way of life compared to civilization, which pollutes and destroys the environment and isn’t sustainable and causes all sorts of psychological problems that aren’t evident in the Caspians. But they have their own challenges to face, of course.

Twilight would be bursting with scientific curiosity, especially about their social structure (free flowing anarchist herds), although she might push against Fluttershy’s dream of returning everyone to the wild. Or maybe they vow to protect the continent from the rest of the world somehow -- not really sure yet.