User blog comment:Hulk10/Dragon Extinction./@comment-8554208-20140529211838

According to the books, it has something to do with Hiccup. And it has been comfirmed that the film series will end similar to the books.

In the books, which are Hiccup's memoirs, the dragons have begun to depart to the sea. So maybe they're not extinct, just hibbernating, which they can do for hundreds, even thousands of years!

Think about that!