Pakicetus is an ancient wolf-like organism that lived 50 million year ago. It had wolf-like ears and nostrils on the front of its skull. Modern whales have a similar ear structure, but their nostrils are on the back of their skull. Aetiocetus lived 25 million years ago, had the same ear structure as both Pakicetus and modern whales, but nostrils in the middle of its skull.