Ordovician

485-443 M.a.

Defined from rocks found in the land of the Ordovices, an ancient Celtic tribe from Wales (UK).

Tetrad spore fossil.

Two continental fragments appear at the edge of Gondwana: Avalonia and Armorica. Some parts of them make up what is currently the southwestern area of the Iberian Peninsula. Invertebrate biodiversity increases and cephalopods, bivalves, echinoderms, etc. proliferate in the oceans. The first fish, known as armoured fish, appear. Spore fossils have been found that prove that plants had already begun the conquest of land (as a result of the adaption of the Charophycean green algae). Large meadows are formed in humid areas with plants similar to current bryophytes.

The expansion of the glaciers and the cooling of the oceans at the end of the Ordovician may have been one of the causes of the first mass extinction which wiped out approximately 25% of the life forms that emerged in the Cambrian period.

Armorican quartzite in Monfragüe National Park (Spain)

Orthoceras regulare (Mollusk, Cephalopod)