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An epoch of the early Tertiary period, spanning the time between 33.7 and 23.8 million years ago. It is named after the Greek words "oligos" (little, few) and "ceno" (new).
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The second earliest period of the Paleozoic era, spanning the time between 505 and 440 million years ago. It is named after a Celtic tribe called the Ordovices.
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Primitive jawless fishes, covered by bony armor, that lived in the Cambrian through Devonian periods.
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