Mass extinction events. Artwork of mass extinction events of life on Earth in strata of rock. Each point of mass extinction is a dark line, where the Earth's fauna suffered extinction rates far higher than normal. At bottom, many invertebrates went extinct in the late Ordovician era (440 million years BP); many bony fish in the late Devonian era (360 Myr BP); many amphibians & early reptiles like Dimetrodon in the late Permian (225 Myr BP); early dinosaurs such as Stegosaurus in the late Triassic (190 Myr BP); advanced dinosaurs like T. rex & Triceratops in the late Cretaceous/Tertiary (65 Myr BP). Extinction events may have been due to volcanic activity on Earth or comet impacts.