ORDOVICIAN PERIOD (485,4-445,2 Ma)
From the old Celtic tribe called Ordovices, who lived in the north of Wales.

Main events: first jawed fish.

Lifeforms: great diversification of marine organisms. Mollusks and arthropods were the most abundant lifeforms, the first coral reefs were formed and jawed fish evolved. Some coastal areas were colonized by very simple and small plants, similar to mosses.

Paleoenvironment: the existing continental plates continued to separate from Gondwana, giving rise to the Reic Ocean. During most part of the Ordovician, the environment was warm, but at the end of the period, there was a widespread cooling that led to a glaciation.

Cobblestones: La Seu grey slate and Rabassa conglomerate.