GEOLOGY & PLANETARY SCIENCE A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site Ordovician period A period of the Paleozoic era that spans the time between the Cambrian and the Silurian, about 490 to 443 million years ago. The Ordovician period is best known for the presence of its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). Related category    • GEOLOGY AND PLANETARY SCIENCE Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP