The K-T Event(Cretaceous–Tertiary extinction event) pales in comparison to the Permian Mass Extinction. More has been published about the extinction of dinosaurs at the K-T boundary than any other group of organisms, which is why it is so widely known.

The Permian–Triassic extinction event, sometimes informally called the Great Dying, was an extinction event that occurred 251.4 million years ago. It was the Earth's most severe extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It caused the extinction of such invertebrates as trilobites, Blastoids, and eurypterids. There is enough evidence to indicate that over two-thirds of terrestrial amphibian, sauropsid ("reptile") and therapsid ("mammal-like reptile") families became extinct. All Permian anapsid reptiles died out except the procolophonids (testudines have anapsid skulls but are most often thought to have evolved later, from diapsid ancestors). Pelycosaurs died out before the end of the Permian. As far as how this great extinction occured is still debated.

As far as how the dinosaurs went extinct, there is enough clear evidence to convince me that it was caused by the Chicxulub Crater impact.

The tsunami in SE Asia and Hurricane Katrina in the Gulf Coast, stick out in my mind.

That's my two cents.:D