An introductory page contains a diagram of the Mesozoic Era showing the Triassic, the Jurassic, and the Cretaceous Periods. A brief text explains that living things have been around for billions of years and the place in time for the Tylosaurus. A twenty-four page story follows which personifies a male Tylosaurus and takes him through a day in his life. He awakes in his watery environment ready to eat. A Pterosaur barely escapes his great jaws. Tylosaurus dives under the water to look for prey, but he must be alert for enemies. A shark with sharp teeth approaches and he quickly changes directions.