The Fifth Mass Extinction, the KT Boundary, or end-Cretaceous, occurred 66 million years ago, with the extinction of 76% of species, including ammonites and non-avian dinosaurs. The Fourth Mass Extinction occurred at the end of the Triassic, 200 million years ago, with the extinction of 80% of species. The Third Mass Extinction occurred at the end of the Permian, 251 million years ago, when 96% of species became extinct. The Second Extinction occurred during the Late Devonian, 375 million years ago, when 75% of living species became extinct. The First Extinction occurred 444 million years ago, with a mass extinction (80-90%) of living species, at the end of the Ordovician. The Sixth is the current one, caused by Homo sapiens since prehistoric times.
