The Cretaceous began 145 million years ago, and it ended 66 million years ago. It was the period when the sea level had its highest point. In the seas, tiny single-celled algae produced huge chalk layers. Different groups of invertebrates had a huge diversity, like the molluscs and the echinoderms. Especially the ammonites and the coral-like rudists were typical for this time. There were also many species of fishes and marine reptiles. On land, the first flowering plants emerged. The dinosaurs had their largest diversity. The largest flying animals existed in the skies. The climate was very warm. At the end, the last big mass extinction happened.
On the picture, you can see sponges, corals, rudists and other kinds of sea life on the seafloor. Above them, different ammonites, belemnites, fishes like Xiphactinus and marine reptiles like Archelon and Mosasaurus are swimming. In the background, you can see a forest with conifers and leafed trees. In this forest, dinosaurs like Tyrannosaurus rex, Triceratops and Iguanodon are walking around. The huge pterosaur Quetzalcoatlus is flying.