The boundary marks the end of the Cretaceous period, which is the last period of the Mesozoic era, and marks the beginning of the Paleogene period of the Cenozoic era. The boundary is associated with the Cretaceous–Paleogene extinction event, a mass extinction, which is considered to be the demise of the non-avian dinosaurs.

Cretaceous–Paleogene boundary - Wikipedia, the free encyclopedia Tuesday, April 1, 2014 @ 10:49pm