The dragons were driven up to the caves by humans after the last ice age. The ice age had already happened before they were driven up. After the KT event, the earth was almost completely wiped out but only the animals that took to the water survived. The land dragons were extinct but still some of the water dragons survived, and over thousand of years, evolved to walk back on land. It’s possible some dragons did live up in the mountains during the ice age, and if so they had a number of ways of surviving. first of all they lived in caves with kept the heat in like an igloo. Second, dragons have a protein in their body that keeps their skin from freezing. If they eat enough, they can also hibernate for many days and beat out most of the cold. they also have fire, but must use it cautiously because they do not have an endless supply. Hope this answers your question and if you have anymore you can watch the movie “dragon’s world” and find out some answers.