It's the largest mass extinction in Earth's history so far. They included 9 species of Paleozoic fauna (some of the few that did actually survive past the Great Dying) and 29 species of modern fauna. Results of the experimental data comparing the hypoxia tolerance and temperature sensitivity of 29 modern and 9 Paleozoic marine faunas. (Marquez et al., PNAS, 2026)Bringing all that data together revealed that Paleozoic fauna tended to be far more sensitive to temperature and oxygen levels than modern fauna. Interestingly, Paleozoic fauna were better able to tolerate low oxygen (hypoxia) so long as they were in a resting state.