in a period known as the Devonian, 进入泥盆纪时期

265. because in the ancient seas,
     因为在古老的海洋中
266. there was to be a changing of the guard.
     即将发生权力转移
267. Seventy million years after the great melt,
     大融化7000万年之后
268. in a period known as the Devonian,
     进入泥盆纪时期
269. the vertebrates made their move.
     脊椎动物开始行动
270. This is Dunkleosteus...
     这是邓氏鱼
271. a descendant of the tiny Arandaspis.
     是微小的阿兰达甲鱼的后代

来自《我们星球上的生命 第一季 第二集 Life on Our Planet S01E02 第一前线》第 268 行