it would soon cover one-fifth of the land. 不久将覆盖五分之一的陆地
especially when it comes to finding a mate. 尤其是在寻找配偶时
...and ensures it has reserves to get through leaner times. 并能够有所储备 以便挺过食物较少的时期
Its huge size allows it to travel large distances in search of food... 巨大的身躯 使它能够长途跋涉寻找食物
it became a harsher, more difficult place to live. 它成为了 一个更恶劣、更难以生存的地方
It was time for the rise of the mammals. 哺乳动物崛起的时候到了
Scanning for fish, it hovers like a hummingbird... 寻找鱼类时 它们像蜂鸟一样