The Maastrichtian is the last stage of the Cretaceous period, occurring approximately 72 to 66 million years ago. It is characterized by significant geological and climatic changes, including rising sea levels and the formation of new marine environments. This period is known for its rich diversity of life, including the dominance of dinosaurs and the emergence of early mammals. The Maastrichtian stage is also notable for the mass extinction event at its end, which led to the extinction of about 75% of Earth's species, including all non-avian dinosaurs. This event marked a major transition in Earth's biological history, paving the way for the rise of mammals and the eventual dominance of birds.