There are whispers, there are rumours and then there’s cemented info….none of the latter with “Jurassic Park 4” just yet – but according to the IMDB, they’ve at least got a story.
"65 million years ago, a terrible disease plagued the Earth which brought about the extinction of the dinosaurs. In the early eighties, when InGen cloned the dinosaurs, they also brought this disease back with them and it has been present ever since before Jurassic Park (thus explaining the sick Triceratops and Brachiosaur). Now this disease has become fully active in the dinosaurs and they’re all getting very ill. When dinosaur carcasses start washing up on the shore of Costa Rica, a team (including Alan Grant) is called out to find out what’s going on. They head to the islands to study the dinosaurs and find out about the disease, known as DX. They also discover the disease is transferable to humans and could possibly bring on our own extinction".
Thanks to Dark Horizons.