Variscan stage

例句：

1. 1. The Variscan stage is characterized by the presence of fossils that are now extinct.
   瓦里卡恩阶的特点是现在已经灭绝的化石的存在。
2. 2. The Variscan stage was a time of significant environmental changes.
   瓦里卡恩阶是一个环境发生重大变化的时代。
3. 3. The Variscan stage is often associated with the rise of the first mammals.
   瓦里卡恩阶常常与第一批哺乳动物的出现联系在一起。