Ordovician
/ˌɔːdəʊˈvɪʃən/adjective
1- Geology of, relating to, or denoting the second period of the Palaeozoic era, between the Cambrian and Silurian periods【地质】（与）奥陶纪（有关）的。
1.1
- as noun the Ordovician the Ordovician period or the system of rocks deposited during it奥陶纪; 奥陶系, 奥陶纪岩石。
The Ordovician lasted from about 510 to 439 million years ago. It saw the diversification of many invertebrate groups and the appearance of the first vertebrates (jawless fish).
词源
late 19th cent.: from Ordovices, the Latin name of an ancient British tribe in North Wales, + -IAN.