Dinotopia (2002)

Pilot Frank Scott takes his sons, half-brothers raised by different mothers, along on an island hopping holiday, but just after spotting an unchartered yet inhabited large isle, the plane crashes at sea and unconscious Frank presumably drowns. Dardevil Karl and cautious, studious David swim ashore and are astonished to be find a society where people cohabit happily with tame, even speaking dinosaurs.

Bickering, the boys fall into the cascade in drift afloat the river. Thus they and Zippo, who came to their rescue with Marion, discover a scarily-well-guarded lost temple, also an entry to the forbidden Underworld. The conservative mayor forbids further exploration and gets the senate to banish them for a year. In a Dino breeding farm, Karl bonds easily, to his own surprise, with a saurian hatched as his life partner, and is tricked by dodgy, scheming 'antiquarian' Cyrus. David passes the training for Skybax pilot with extreme effort.

All of Dinotopia seems to be falling apart and prey to the pterodactyls as the sun-stones, its power source, systematically break down. Zippo helps the brothers escape from arrest to meet Cyrus on a quest for stones and the way off the island a late explorer discovered. It turns out to be an elaborate trap at the old temple, where they meet up with father Karl, whom they had presumed dead, while Cyrus perishes in the explorer's submarine after stranding the Scotts, who seek their own way out.