Toward the end of the Age of Dinosaurs, during a time known as the Late Cretaceous, a new type of giant predator appeared along the southern coasts of North America. It was a huge species of crocodylian called Deinosuchus. Neither a crocodile nor an alligator, it was an ancestor of both modern groups; it reached weights of many tons and it had some features unique to its own species. Average-sized individuals were bigger than the carnivorous dinosaurs with which they co-existed; the largest specimens were the size of a T-rex. King of the Crocodylians, the biography of these giant beasts,...