Although the name of the film points to a specific time in the Mesozoic era, the animals depicted in the story lived during different periods.

Most of the dinosaurs appearing in the story (such as Tyrannosaurus, Velociraptor, and Triceratops) lived during the Cretaceous period, which was the last of the Mesozoic era. Representatives of Jurassic period dinosaurs appearing in history, however, were Brachiosaurus and Dilophosaurus.