Climate and Geography During the Cretaceous, the inexorable breakup of the Pangaean supercontinent continued, with the first outlines of modern North and South America, Europe, Asia and Africa taking shape. Conditions were as hot and muggy as in the Jurassic, with the added twist of rising sea levels and the spread of endless swamps--yet another ecological niche in which dinosaurs could prosper.
Terrestrial Life It was during the Cretaceous that dinosaurs really came into their own. Thousands of species roamed the slowly separating continents, including theropods like T. Rex, ornithopods like Iguanodon, and ceratopsians like the elaborately horned Styracosaurus and Triceratops. Mammals still kept to themselves; they would only emerge from the shadows after the dinosaurs were wiped out in the K/T Extinction.
Aquatic Life Toward the beginning of the Cretaceous, ichthyosaurs vacated the scene, to be replaced by aquatic reptiles like Mosasaurus and Tylosaurus; gigantic pliosaurs like Kronosaurus and plesiosaurs like Elasmosaurus still preyed on fish, squids and mollusks. A new breed of bony fish, known as teleosts, roamed the seas in enormous schools.
Avian Life By the end of the Cretaceous, pterosaurs had finally attained the enormous sizes of their cousins on land and in the sea, Quetzalcoatlus being the most spectacular example. This was the breed’s last gasp, though, as they were gradually crowded out of the sky by the first true birds (which paleontologists believe evolved from land-dwelling dinosaurs, not pterosaurs).
Plant Life The main innovation of the Cretaceous was the evolution of flowering plants, which spread across the separating continents, along with thick forests and other kinds of dense, matted vegetation. At the end of the Cretaceous, 65 million years ago, a meteor impact raised huge clouds of dust, blotting out the sun and causing most of this vegetation to die out. The herbivorous dinosaurs that fed on the plants died, as did the carnivorous dinosaurs that fed on the herbivorous dinosaurs. The way was now clear for the evolution of mammals.
