Dinotopia

From the introduction: Welcome, Jumper, to the island nation of Dinotopia. This isolated island, a few hundred miles across, has a variety of terrains and is surrounded by the deadly Razor Reef and year-round storms. These obstacles make it impossible to leave Dinotopia—but really, why would anyone want to? This tropical paradise is home to dinosaurs that survived the mass extinction at the end of the Mesozoic Era by taking shelter in a system of caves under the island. Later, humans came to live in Dinotopia and helped to create a harmonious and peaceful land. Dolphin-backs—those humans who have washed ashore instead of being born in Dinotopia—are the only source of knowledge of the outside world, and the last one to arrive was in 1944.