Some older (medieval) civilizations apparently `domesticated’ dragons (if it can be really called domestication) to the point that they would accept riders on their backs, and could thus be used as part of the war machinery (used to `melt castles and burn cities’, Jon Snow, Game of Thrones). This is thought to be the case of the continent that existed just west of modern day Europe, before cataclysmic geological evolution reduced its size and left a number of smaller islands.
Exploration of the waters around the islands, should yield evidence confirming this.