Ordovician From Wikipedia, the free encyclopedia Jump to: navigation, search Artist impression of the Ordovician Sea. The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era.
It follows the Cambrian period and is followed by the Silurian period.
The Ordovician extinction event is particularly apparent in the chart of family diversity (second chart on this page).Some scientists even hold out the faint hope that in poorly explored deep sea environments, trilobites may still exist, a holdover from truly ancient times.*The chart above (and below) are based on the International Commission of Stratigraphy 2008 revision of the Geological Time Scale.See the full set of current charts in UNESCO and US standard colors.Molluscs, which had also appeared during the Cambrian, became common and varied, especially bivalves, gastropods, and nautiloid cephalopods.It was long thought that the first true vertebrates (fish - Ostracoderms) appeared in the Ordovician, but recent discoveries in China reveal that they probably originated in the Early Cambrian.