There is actually a cool theory that au ra are children of bahamut who originally had white scales and this other one who had black scales.
And as far as FFxiv is concerned, dragons are not lizards and more of a race of their own.
And are VERY old and are not from our world.

Shiva fell in love with a dragon who we can only assume was a hyur.
We can assume they probably did lay with each other.