In Middle Cretaceous Argentina, Marven searches for the largest dinosaurs of all time. He encounters a herd of Argentinosaurus, one of the largest sauropod dinosaurs, and observes the long and drawn-out hunt of the sauropods by one of the largest predatory dinosaurs, Giganotosaurus. During his journey, Marven also uses a small plane to fly with pterosaurs such as Pteranodon and Ornithocheirus, and he also encounters the massive crocodyliform Sarcosuchus.

Nigel searches the deserts and forests of Cretaceous Mongolia for Therizinosaurus, an obscure dinosaur with massive fossil claws, believing it to have been a huge carnivore. Throughout his journey, Marven comes face-to-face with dinosaurs such as Saurolophus, Protoceratops, Mononykus, Velociraptor and Tarbosaurus, a close relative of the famous Tyrannosaurus rex. Once Marven finds live Therizinosaurus he discovers them to have been a bizarre type of giant plant-eating theropod dinosaur.