At the end of Jurassic Park III, we see the Pteranodons flying away from Isla Sorna.
Eric: "Where do you think they're going?"
Dr. Grant: "I don't know, maybe just looking for a... new nesting grounds. It's a whole new world for them."
At the end of the new film, Jurassic World: Fallen Kingdom, we're presented with a similar image. Dinosaurs are now on the loose on the North American mainland. In a post-credits scene, we see Pteranodons landing on the Paris Las Vegas' Eiffel Tower replica. This seems to be the set-up for the next Jurassic World film, in which dinosaurs roam the world.
The Wikipedia article on Jurassic World does mention that the early drafts were built on the idea of dinosaurs getting off the island:
In January 2003, Jeff Goldblum said he had been asked to stay available for a possible return of his character Ian Malcolm. At the end of the month, it was reported that the story would involve dinosaurs migrating to the Costa Rican mainland.
Was the end scene in Jurassic Park III explicitly meant as a set-up for a sequel that didn't get made?