THE CAMBRIAN RADIATION, which commenced around 550 million years ago, arguably ranks as the single most important episode in the development of Earth’s marine biota. Diverse benthic communities with complex tiering, trophic webs, and niche partitioning, together with an elaborate pelagic realm, were established soon after the beginning of the Cambrian period. This key event in the history of life changed the marine biosphere and its associated sediments forever.