Just yesterday, I learned about a type of proto-dragon from Korean mythology.
Korean folk mythology states that most dragons were originally Imoogis, or lesser dragons, which were said to resemble gigantic serpents, there are a few different versions of Korean folklore that describe what imugis are and how they aspire to become full-fledged dragons.
By other accounts, and Imugi is a proto-dragon which must survive one thousand years in order to become a fully fledged dragon, in either case they are said to be large, benevolent, python-like creatures that live in water or caves, and their sighting is associated with good luck.
source: https://engkers.blogspot.com/2016/10/imoogi-korean-dragon-mythology.html