Ordovician
Proper noun 1. The Ordovician Period: A major division of geological time within the Paleozoic Era, following the Cambrian Period and preceding the Silurian Period. It is characterized by the diversification of marine life, including the appearance of early corals, nautiloids, and jawless fish, and ended with a significant mass extinction event.
The word "Ordovician" is used almost exclusively as a proper noun to refer to this specific geological period. It is typically capitalized and often functions adjectivally to describe rocks, fossils, or events from that time. - The Ordovician Period saw a great expansion of life in the seas. - These limestone deposits contain abundant Ordovician fossils. - The end-Ordovician extinction was one of the largest in Earth's history.
- In compound geological terms: When used adjectivally before other nouns, it specifies the time origin.
- Ordovician shale
- Ordovician fauna
- Ordovician-Silurian (adj): Pertaining to the boundary or events spanning the end of the Ordovician and the beginning of the Silurian Period.
- The Ordovician-Silurian boundary is marked by a global glaciation.
- Ordovician Period: The full formal name.
- Middle Paleozoic: A broader, less specific temporal description.
- Great Ordovician Biodiversification Event (GOBE): A significant evolutionary event during this period involving a major increase in the diversity of marine life.
- Late Ordovician mass extinction: The extinction event that defines the end of the period.
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from 500 million to 425 million years ago; conodonts and ostracods and algae and seaweeds
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