Anyone else notice that the mystical land of adventure in FiM, a Canadian-produced show, is really just... Mexico?
Haha, yes, Canada is America's hat, et cetera.
But let's follow that train of thought for a moment. Now, we've seen mythical creatures from other Earth belief systems before the Daring Do arc started pulling from Aztec mythology. Basilisks, griffins, minotaurs, manticores... so it was no big leap to add an ahuizotl, or even reference Quetzalcoatl in dialogue.
Here's the big leap:
"Daring Don't" established that the Daring Do series was, essentially, nonfiction. The author of the books was Daring Do herself under a pseudonym, writing about her adventures in Equestria. So characters, places, and events in the books are real.
In "Daring Don't", Rainbow Dash points out that "Ahuizotl has sought control of the Tenochtitlan Basin since book three."
Hold up... Tenochtitlan is a real place. Mexico City is built on its ruins.
As far as I'm concerned, this has cemented my personal headcanon -- that Equestria is North America, far in the future, and ponies have replaced humans as the dominant species on the planet.
Check out the official map of Equestria:
The shoreline's not right, that's true. There's a big bay south of Baltimare that doesn't exist today. And mythical creatures would have had to evolve from our current species, to populate Equestria with the basilisks, manticores, and griffins we all know and love.
But there's a simple answer to all of that, really: nuclear war.
That big bay, south of Baltimare? Looks to me like Washington D.C. got nuked so hard all that was left was a crater... which filled with water once the sea levels rose because the polar ice caps melted thanks to the extra greenhouse effect caused by atmospheric dust and ash. That also explains the changed coastlines... and the radiation helped trigger the genetic mutations (perhaps helped along by any genetic experiments humanity had been carrying out before the war) that resulted in mythical creatures and sentient horses taking over the planet.
After the precursors to the ponies we know and love evolved, as they resettled the changed North America, some human terminology and technology stuck. Linguistic drift coupled with an equine focus meant "Manhattan" became "Manehattan"; doorknobs hung around, because doors have always had them... as far as the ponies knew. Over the millenia, ponies continued evolving, and references to their prehistory -- our modern day -- slowly faded.
You heard it here first, folks: global warming and nuclear war will give us real-life ponies.