Today, however, some 50 million years after their quadrupedal ancestors first waded into the warm waters of Tethys, whales are singularly sleek.

• 不过，鲸豚的四足祖先首次进入特提斯海的温暖水域，距今已有5000万年，时至今日，鲸豚造型已极为简洁。