Or·do·vi·cian /ˌɔrdəˈvɪʃən/
奧陶紀,奧陶系(a.)奧陶紀的
Or·do·vi·cian a. Geol. Of or pertaining to a division of the Silurian formation, corresponding in general to the Lower Silurian of most authors, exclusive of the Cambrian. -- n. The Ordovician formation.
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Ordovician
n : from 500 million to 425 million years ago; conodonts and
ostracods and algae and seaweeds [syn: Ordovician period]