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Geological periods are annotated (by abbreviation and colour) above.
The Permian–Triassic extinction event is the most significant event for marine genera, with just over 50% (according to this source) failing to survive.
According to this theory one of these extinction pulses occurred at the end of the Guadalupian epoch of the Permian.The ammonoids, which had been in a long-term decline for the 30 million years since the Roadian (middle Permian), suffered a selective extinction pulse 10 million years before the main event, at the end of the Capitanian stage.In this preliminary extinction, which greatly reduced disparity, or the range of different ecological guilds, environmental factors were apparently responsible.However, it is now possible to date the extinction with millennial precision.U–Pb zircon dates from five volcanic ash beds from the Global Stratotype Section and Point for the Permian–Triassic boundary at Meishan, China, establish a high-resolution age model for the extinction – allowing exploration of the links between global environmental perturbation, carbon cycle disruption, mass extinction, and recovery at millennial timescales.
In well-documented Late Triassic deposits, fossils overwhelmingly consist of modern fossil insect groups.