Mass extinctions

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 * 1)  (End Ordovician or O–S): 450–440 Ma (million years ago) at the – transition. Two events occurred that killed off 27% of all families, 57% of all genera and 60% to 70% of all species. Together they are ranked by many scientists as the second largest of the five major extinctions in Earth's history in terms of percentage of  that became extinct.
 * : 375–360 Ma near the – transition. At the end of the in the later part(s) of the, a prolonged series of extinctions eliminated about 19% of all families, 50% of all  and at least 70% of all species. This extinction event lasted perhaps as long as 20 million years, and there is evidence for a series of extinction pulses within this period.
 * 1)  (End Permian): 252 Ma at the – transition. Earth's largest extinction killed 57% of all families, 83% of all genera and 90% to 96% of all species (53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species, including s). The highly successful marine arthropod, the, became extinct. The evidence regarding s is less clear, but new taxa became dominant after the extinction. The "Great Dying" had enormous evolutionary significance: on land, it ended the primacy of . The recovery of vertebrates took 30 million years, but the vacant  created the opportunity for s to . In the seas, the percentage of animals that were  dropped from 67% to 50%. The whole late Permian was a difficult time for at least marine life, even before the "Great Dying".
 * 2)  (End Triassic): 201.3 Ma at the – transition. About 23% of all families, 48% of all genera (20% of marine families and 55% of marine genera) and 70% to 75% of all species became extinct. Most non-dinosaurian s, most s, and most of the large s were eliminated, leaving s with little terrestrial competition. Non-dinosaurian archosaurs continued to dominate aquatic environments, while  continued to dominate marine environments. The  lineage of large amphibians also survived until the Cretaceous in Australia (e.g., ).
 * 3)  (End Cretaceous, K–Pg extinction, or formerly K–T extinction):   at the   –   transition interval. The event formerly called the Cretaceous-Tertiary or K–T extinction or K–T boundary is now officially named the Cretaceous–Paleogene (or K–Pg) extinction event. About 17% of all families, 50% of all  and 75% of all species became extinct. In the seas all the,  and  s disappeared and the percentage of  animals (those unable to move about) was reduced to about 33%. All non-avian s became extinct during that time. The boundary event was severe with a significant amount of variability in the rate of extinction between and among different s. s and s, the latter descended from  dinosaurs, emerged as dominant large land animals.