Scientists wondered for a long time just how whales are related to land mammals,
especially the largest land mammal, the elephant. They believed there must have been
some kind of in-between mammal that lived partly in the sea and partly on the land.
They had no evidence for such an animal, however, until the discovery of the bones of
an animal scientists have called "Pakicetus." This large mammal, which was alive 50
million years ago,