@thps48  
If they stick to G1 lore, Spike’s Egg was delivered to Celestia by Scorpan as a gift, from an area that was quite far from any place near equestria. This would easily explain “why are there no other non-winged dragons?” because they (spike) are from another continent altogether.
 
How Scorpan ended up in possession of the egg is anyone’s guess.

@Daneasaur  
Well, right, his winglessness would of course give them a different use to that of a winged dragon. Meanwhile, I kind of think the term Earth Dragon is odd sounding because he’s the only dragon without wings. It’d probably sound better if we bloody well knew what attributes his parents have that they gave him. lol

@thps48  
Some birds do, using them as flight goggles, but also aquatic animals often have them as well.
 
The difference being that this trait is a reflex upon the environment under normal situations.
 
IE: A bird uses it while diving, a croc/gator uses it while diving.
 
I still stress that there isn’t anything wrong with the idea of their being winged dragons earth dragons, and even sea/magic centered dragons.
 
Anyway, Spike’s most prominent features are: Lack of wings, thick scales, and great skill in digging. All signs point that he’s an earth dragon.

@Daneasaur  
And birds don’t have the same membrane as lizards and dinosaurs? I’m actually asking. I definitely don’t know for reals how birds protect their eyes from wind and debris. X3

This just forever shall be more backing to the claims that spike is an earthdragon and would naturally need the membrane to prevent dirt and debris from getting in his eyes while digging.

Basically, those are see-through eye-lids for the purpose of eye protection. Some reptiles actually go to sleep like that (ewww), which is pretty cool.

I love this scene

Many vertebrates have it as a protection for their eyes when hunting. You can say its a pair of goggles.

Invisible Rarity.

@Too_Offensive  
Snakes don’t have any eyelids, they have a brille(transparent scale/layer of skin) but that doesn’t movie.

I know crocodiles do that when they go under water. Dunno about snakes. I’d assume desert snakes have a setup like that to keep sand out of their eyes.

The terrible power of the Pimp Hat of Avarice.

It really makes me curious. Do snakes really do that with their eyes?

The fact that they gave him a second pair of eyelids instead of just having him make a scary face is amazing.