Marine invertebrates suffered the greatest losses during the P–Tr extinction.
Evidence of this was found in samples from south China sections at the P–Tr boundary.
These cyclical flora shifts occurred a few times over the course of the extinction period and afterwards.
In this preliminary extinction, which greatly reduced disparity, or the range of different ecological guilds, environmental factors were apparently responsible.
Here, 286 out of 329 marine invertebrate genera disappear within the final 2 sedimentary zones containing conodonts from the Permian..