Did you know ponies aren’t the same thing as young horses? I didn’t. I am shocked and furious.
Um…watching Friendship Is Magic would disabuse you of this concept posthaste. All the characters, young and old, are referred to as ponies, with younger ones referred to as foals in general, colts and fillies specifically.
I’m still wondering, though, if ponies are an entirely different species from horses.
Nope. Ponies and horses are the same species—ponies are just smaller. There are ‘pony breeds’ and ‘horse breeds’, and sometimes they correlate (a Pony of the Americas is basically a pony-sized Appaloosa), and sometimes they’re their own thing (there is no horse-version of a Norwegian Fjord). The cutoff for an animal is 14.2 hands, though, breed can complicate things (Arabians are often below 14.2 hands, but we call them horses anyways because they aren’t fat like ponies.).
And, of course, further complicating the matter is that over in the UK and possibly elsewhere, any kid’s horse, regardless of size or breed, is referred to as a pony.