Scientists wondered for a long time just how whales are related to land mammals. They believed that there must have been some kind of in-between mammal. It would have lived partly in the sea and partly on land. However, they had no evidence of such as animal. The discover of "Pakicetus" seems finally to be proof of this theory. The bones of Pakicetus show that this large mammal lived 50 million years ago. It looked a lot like a whale.