知识贝壳
知识贝壳
所属栏目：英汉双解生物学
The second most recent pe-riod of the Paleozoic era,some 355 - 280million years ago. It is characterized by theevolution on swampy land of amphibians,afew primitive early reptiles,and giant ferns.Aquatic life included sharks and coela-canths. The period i ......（本文共 474 字 ） [阅读本文] >>