Well, if the plot follows what I think it will, then the 4th film could pretty much take the place of JP 3 as the sequel to The Lost World. In Jurassic Park, velociraptors were escaping from Isla Nublar. In The Lost World, we learned that the meals the park scientists fed the dinosaurs contained
a certain protein or enzyme (Don't have the book with me
) that supressed a disease that was inherent in the dinosaur population. Now that their diet consists of the island's flora and fauna, that disease would likely strengthen. So now you have these diseased dinosaurs reaching the mainland packing an internal viral threat. There's a wealth of ideas in that which could include Bio-Syn and most of the original cast. And Carnotaurus. Please remember the Carnotaurus!!!