Extinction Rates over geological time

Rates of extinction (measured as the percentage of taxonomic families that disappear in the fossil record in each successive period) are highly variable over time. The two major episodes are the "Permian Die-off" at the end of the Paleozoic, which affected mainly marine invertebrates, and the K/T Boundary event (Cretaceous / Tertiary) at the end of the Mesozoic, which affected terresterial dinosaurs. Note that, despite extinctions, the total taxonomic diversity has generally increased over time (red line).