Smack in the middle of this amazing transformation is Ambulocetus: a toothy predator the size of a sea lion -- and a striking example of a mammal order in transition.

处于这一惊人转变中间的是走鲸：一种长着牙齿的捕食者，体型与海狮相当——也是哺乳动物目次转变的一个显着例子。