In 1879, Charles Lapworth gave name to a new geological period after a pre-Roman tribe of Ordovices in Wales.

Paleogeography

In the Ordovician, the northern hemisphere was covered almost entirely by a vast ocean. Most of the land was concentrated close to and south of the equator.

Most of today's landmasses (southern Europe, Africa, South America, Antarctica, and Australia) have been a part of Gondwana since the Cambrian. This mega-continent migrated south, where it eventually arrived at the end of the Ordovician.

Other landmasses were separated by oceans, such as the Iapetus Ocean, which separated continents of Baltica, Avalonia and Laurentia. As it closed, the continents converged, starting the Caledonian orogeny.

Climate

For most of the Ordovician period, Earth had a temperate and warm climate. But, with Gondwana reaching the South Pole, extensive ice sheets began to form, starting the first Paleozoic ice age.

Life on Earth

Great Ordovician Biodiversification Event

The large, warm, shallow seas helped the diversification of marine life. Nautiluses, mussels, brachiopods, and snails experienced a boom in the evolution of new species and in numbers. Solitary horn corals (Rugosa) and hexagonal colonial corals (Tabulata) were the Ordovician reef-forming organisms. This unprecedented period of life’s on Earth history has been nicknamed "The Great Ordovician Biodiversification Event".

Graptolites

Graptolites appeared in the Ordovician, and they were one of the first animals to thrive in open sea environments. They were hemichordates related to today's Pterobranchs, small worm-shaped animals. Graptolites are important index fossils.

Colonization of land

The oldest spores discovered so far, indicating the plant colonisation of land, date back to the early Ordovician. They likely belonged to the relatives of modern mosses. Slightly younger are the traces of fungal hyphae. The oldest trace fossils of animals on land, likely distant relatives of horseshoe crabs and arachnids, also come from the Early Ordovician.

Vertebrates

Individual bones and soft tissue traces were recovered from Cambrian rocks, but the oldest complete unequivocal skeletons come from the Ordovician. They belong to a jawless armoured fish commonly known as ostracoderms, although their taxonomic placement is still disputed. A typical Ordovician fish had a head composed of large bony plates and usually lacked paired fins.

The great extinction

The glaciation that took place at the end of the Ordovician was short-lived yet extensive. The changes in sea levels, as a consequence of that glacial period, led to mass extinction, in which about 85% of the species vanished.

Do you know...

The Ordovician glaciation caused a drop in sea levels of about 50 meters.