There is evidence of a lot of mass extinctions. The Big Five is just the biggest 5 we know off (all of them feature atleast 75% of all species becoming extinct

There is evidence of a lot of mass extinctions. The Big Five is just the biggest 5 we know off (all of them feature atleast 75% of all species becoming extinct on a relatively short timeframe, with the quickest being the KT which lasted at most a thousand years, the biggest of them, the PT event, making 95% of all species extinct). For smaller extinction events, Wikipedia lists about 30 of them. But those aren't nearly as interesting because they didn't have that much impact.