The Ordovician biodiversification event, or radiation, of 500 million years ago (mya) was one of the most significant events in the history of life, and in fact involved a greater increase in diversity at the family and genus level than did the more popularly known Cambrian radiation, which occurred 540 mya. (Recall that families comprise genera, which in turn comprise species.) During the Ordovician radiation the diversity of marine families nearly tripled, and those groups of animals that came to dominate the next 250 million years were established.