Ordovician
adjective geology specialized uk/ˌɔː.dəˈvɪʃ.ən/ us/ˌɔːr.dəˈvɪʃ.ən/
奥陶纪的（距今约4亿8千5百万年至4亿4千5百万年前间，此时水中已有许多动物包括脊椎动物，但是陆地上还没有动物）
from or referring to the period of time between about 485 and 445 million years ago, in which there were many different types of animals in the sea, including vertebrates (= animals with back bones), but no life on land
the Ordovician period 奥陶纪
Ordovician fish 奥陶纪的鱼类
the Ordovician
noun [ S ]
奥陶纪
the Ordovician period