I stumbled across Dragontooth Crater last night. Found a sleeping dragon lying on the ground in front of a word wall. I start attacking him, he gets up, flies around some, and lands again. I continue attacking, his health level is phenomenal! But, as I run his health bar down to nothing, he just sits there, won't die. He's also glitched, and now has his head stuck in the ground. Is it the glitch, or can he not be killed because he's part of the main quest which I have not finished? I've attacked him numerous times after his health runs out, he won't die.

I've beaten the MQ, and I don't remember this being part of it.

Supposedly a dragon will be there randomly. I guess he just glitched somehow, and became invincible at the same time.