But this blossoming of life was interrupted within 40 or 50 million years by the fourth mass extinction, which arrived about 200 million years ago. Roughly 75 percent of all species went extinct in this end-Triassic extinction that preceded the Jurassic period. The cause of this extinction is uncertain, but lower sea levels and the start of the volcanic rift that eventually produced the Atlantic Ocean might have played a role. Most large vertebrate predators in the ocean were killed off and species of sponges, corals, brachiopods, nautiloids, and ammonoids were badly hit as well. This
...more
