As a reminder, the "Big 5" mass extinction events are the following : The Late Ordovician mass extinction (~445–444 Ma) The End Devonian mass extinction event (~372 Ma) The Permian-Triassic extinction event aka The Great Dying (~252 Ma) The End Triaasic mass extinction event (~201 Ma) The Cretaceous-Paleogene Mass Extinction event, the asteroid and dinosaur one (~66 Ma). The “Big Five” mass extinction events obviously stand apart statistically and in terms of ecological impact, but I was wondering: if you had to make a list of “medium-tier” extinction/crisis events, what events would you include? By that I mean major global biotic disruptions that significantly reshaped ecosystems and caused substantial turnover/extinctions, but are not traditionally counted among the Big Five.…