An early story idea would partially involve dinosaurs migrating to the Costa Rican mainland. A team of experts, including Dr. Alan Grant and Dr. Ian Malcolm, would chart an expedition to an offshore island and discover the dinosaurs breeding freely. Part of the plot would involve the characters devising a way to restrict the spread of the dinosaurs and prevent an ecological disaster. Early concept art also depicted genetically engineered human-dinosaur mercenaries. Monahan's first draft of the script was finished in July 2003; the story was not set in a jungle, as in previous films. Monahan subsequently left the project to work on Kingdom of Heaven. In 2004, Frank Marshall joined the project as a producer, and Monahan was replaced by John Sayles, who wrote two drafts of the script. In one draft, a new character, a mercenary named Nick Harris, would be charged with training a team of genetically modified Deinonychus for use on rescue missions and to combat drug dealers. The concept of a human who trains dinosaurs came from Spielberg. By April 2005, the film had been postponed, as Spielberg was dissatisfied with the script revisions.