5 million years ago. the impact of an asteroid killed off Tyrannosaurus Rex. But this occurred at a time of violent volcanic eruptions and slow weather changes in the sea that some palaeontologists believe caused their extinction. What really happened to end the age of dinosaurs and begin the age of mammals is still somewhat of a mystery .

In the middle of the vast badlands of Montana sits a place called Hell Creek. It's a fossil hunter's goldmine with more skeletons of Tyrannosaurus Rex than any other place on earth. Here in the "Valley of the T-Rex" lies evidence of the lost world where armour plated, Ankylosaurus and horned Triceratops feed on low growing plants, where duck-billed Edmontosaurus nest and lay their eggs, where small crocodilians, insects and early birds like Avisaurus fight for survival. Discovery Channel travels along with famed palaeontologist "Jack" Horner. as he continues his search for the lost world of the most famous dinosaur of all time.