Definitions for "Ordovician"
Of or pertaining to a division of the Silurian formation, corresponding in general to the Lower Silurian of most authors, exclusive of the Cambrian.
Period from 500 Ma to 435 Ma
Geologic period that occurred roughly 438 to 505 million years ago. During this period, the first fish and fungi species appear.
Keywords:  formation
The Ordovician formation.