During the early Ordovician period the first vertebrate fish have been found.  Graptolites and corals also flourished.

The Ordovician period follows the Cambrian period.

The Ordovician period started at an apparently minor extinction event some time 490 million years ago and lasted for about 50-80 million years. It ended with a major extinction event 443.5 million years ago that wiped out 60% of marine genera. The dates cited are recent radiometric dates and vary slightly from those used in other sources.

Ordovician rocks contained abundant life and contain major oil and gas reservoirs in some regions.

The Ordovician is usually broken into

Lower (Tremadoc and Arenig)

Middle (Caradoc, Llanvirn, Llandeilo)

and

Upper (Ashgill) subdivisions.

In North America and Europe, the Ordovician was a time of shallow continental seas rich in life. Trilobites (an extinct class of Arthropods) and Brachiopods (one of the major animal phyla) in particular were rich and diverse. The first Bryozoa (tiny creatures with a ring of tentacles surrounding the mouth) appear in the Ordovician as do the first coral reefs.

Solitary corals date back to the Cambrian at least. It was long thought that the first true vertebrates (fish) appeared in the Ordovician, but recent discoveries in China reveal that they probably originated in the Early Cambrian. Now-extinct marine animals called graptolites thrived in the oceans. The southern continents were collected into a single continent called Gondwana during the Ordovician. Gondwana started the period in equatorial latitudes and drifted toward the South Pole during the period.

As with North America and Europe, Gondwana was largely covered with shallow seas during the Ordovician. By the end of the period, Gondwana had neared or approached the pole and was largely glaciated - a glacier is a large, long-lasting flow of ice that is formed on land and moves in response to gravity.