The tie to water 由于蛋的进化

261. Its egg developed a protective shell
     它的卵进化出了一层保护性外壳
262. that held the embryo in its own private pool of fluid.
     将胚胎保护在“私家泳池”之中
263. Inside, the young could develop safely without drying out.
     幼崽在其中能够安全地发育 而不会干涸
264. The tie to water
     由于蛋的进化
265. was finally broken by the evolution of this amniotic egg.
     与水的联♥系♥终于被断开
266. Known as the amniotes,
     这些羊膜动物
267. these creatures could colonize the drier land
     能够以两栖动物无法做到的方式

来自《我们星球上的生命 第一季 第三集 Life on Our Planet S01E03 入侵大地》第 264 行