End-Cretaceous Extinction

The end-Cretaceous extinction is best known of the "Big Five" because it was the end of all dinosaurs except birds (the non-avian dinosaurs). It also created opportunities for mammals. During the Mesozoic Era dinosaurs dominated all habitats on land. Mammals remained small, mostly mouse to shrew-sized animals and some paleontologists have speculated that they might have been nocturnal to avoid dinosaurs. All that changed with the end-Cretaceous extinction. Mammals survived and took over. The following Paleogene Period saw the evolution of everything from bats to whales. Without the end-Cretaceous extinction, we might not be here to learn about it. end_Cret_on_time_scale

When did it happen?

The extinction occurred at the end of the Cretaceous Period, about 65.5 million years ago.

Who became extinct?

In addition to the non-avian dinosaurs, vertebrates that were lost at the end of the Cretaceous include the flying pterosaurs, and the mosasaurs, plesiosaurs and ichthyosaurs of the oceans. Important marine invertebrates also disappeared, including ammonites, groups of cephalopods and some bivalves, such as the reef-building rudists and some relatives of modern oysters. Below are examples of vertebrate groups that became extinct at the end_Cretaceous event.