 The sperm whale 's lower jaw is very narrow and underslung . The sperm whale has 18 to 26 teeth on each side of its lower jaw which fit into sockets in the upper jaw . The teeth are cone @-@ shaped and weigh up to 1 kilogram ( 2 @.@ 2 lb ) each . The teeth are functional , but do not appear to be necessary for capturing or eating squid , as well @-@ fed animals have been found without teeth or even with deformed jaws . One hypothesis is that the teeth are used in aggression between males . Mature males often show scars which seem to be caused by the teeth . Rudimentary teeth are also present in the upper jaw , but these rarely emerge into the mouth . Analyzing the teeth is the preferred method for determining a whale 's age . Like the age @-@ rings in a tree , the teeth build distinct layers of cementum and dentine as they grow . 
