 Ancient sperm whales differ from modern sperm whales in tooth count and the shape of the face and jaws . For example , Scaldicetus had a tapered rostrum . Genera from the Oligocene and Miocene had teeth in their upper jaws . These anatomical differences suggest that these ancient species may not have necessarily been deep @-@ sea squid hunters like the modern sperm whale , but that some genera mainly ate fish . Contrary to modern sperm whales , most ancient sperm whales were built to hunt whales . Livyatan had a short and wide rostrum measuring 10 feet ( 3 @.@ 0 m ) across , which gave the whale the ability to inflict major damage on large struggling prey , such as other early whales . Species like these are collectively known as killer sperm whales . 
