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 shows the place in time for the Apatosaurus. A twenty-two page story follows which personifies a female Apatosaurus and takes her through a day in her life. She is feeling the weight of eggs in her body as she eats plants and watches for predators. While her head is deep in a bush, a pack of carnivorous Ceratosaurus come up behind her and stare at her hungrily.