Paleontologists have uncovered a wealth of whale fossils spanning the Eocene epoch, the time between 55 million and 34 million years ago when archaic whales, or archaeocetes, made their transition from land to sea.

• 古生物学家已经找到了丰富的始新世古鲸化石，也就是现生鲸豚的祖先；他们发现古鲸是在5500~3400万年前的始新世，从陆栖动物演变成海栖动物的。