 Early archaeocetes such as Pakicetus had the nasal openings at the end of the snout , but in later species such as Rodhocetus , the openings had begun to drift toward the top of the skull . This is known as nasal drift . The nostrils of modern cetaceans have become modified into blowholes that allow them to break to the surface , inhale , and submerge with convenience . The ears began to move inward as well , and , in the case of Basilosaurus , the middle ears began to receive vibrations from the lower jaw . Today 's modern toothed whales use their melon organ , a pad of fat , for echolocation . 
