The mammals had gone from tiny land animals... 哺乳动物从微小的陆地动物

300. As the planet continued to cool,
     随着地球持续降温
301. it fed an explosion of life...
     生命爆♥炸♥式发展
302. allowing the giants of today to evolve.
     使如今的巨兽得以进化
303. The mammals had gone from tiny land animals...
     哺乳动物从微小的陆地动物
304. to being bigger than dinosaurs.
     变得比恐龙还大
305. With each giant breath,
     通过大口呼吸
306. they use oxygen far more effectively than Maiacetus.
     它们利用氧气的效率远高于慈母鲸

来自《我们星球上的生命 第一季 第七集 Life on Our Planet S01E07 地球继承者》第 303 行