251 million years ago, up to 96% of marine species and 54% of marine families were lost in the end-Permian extinction event. (Hallam, 1997)

Comparing species that survived and those that perished can provide clues about the crisis. Optimally, one would hope to see clear patterns in the fossil record; for example, photoautotrophs suffering most, larger animals that died quickly or specialists disappearing in a particular way. Evidence for selectivity such as this is hard to come by, but some conclusions can be drawn. Of course, species with wide ranging habitats, food sources and environmental tolerances will likely be among extinction survivors.

By surveying survivors and victims of the Permo-Triassic extinction, Tony Hallam et al. (Hallam, 1997) argue that survivors share a few common traits; the ability to live in low oxygen conditions and dwarfism. Surviving foraminifera, the brachiopods Lingula and Crurithyris, the bivalves Claraia and Eumorphotis and ostracods are species exhibiting the ability to live in a low oxygen environment. This observation, along with composition of boundary strata, helps to show the anoxic environment of the PTB.

In the Lower Triassic Werfen Formation in northern Italy, marine strata record deposition in a number of settings, from peritidal to outer ramp environments. This range of environments helps to minimize facies related effects in faunal recovery analyses. In this area, the extinction of shelly taxa appears as the most rapid, followed by echinoderms and trace fossil taxa. A marked decrease in macrofossil and ichnofossil diversity occurs during the Smithian (249.7 Mya) with the appearance of increased terrigenous sediment. This sediment possibly reflects increased run-off from continents and brackish conditions. (Twitchett, 1999)