 Odontocetes are known as toothed whales ; they have teeth and only one blowhole . They rely on their well @-@ developed sonar to find their way in the water . Toothed whales send out ultrasonic clicks using the melon . Sound waves travel through the water . Upon striking an object in the water , the sound waves bounce back at the whale . These vibrations are received through fatty tissues in the jaw , which is then rerouted into the ear @-@ bone and into the brain where the vibrations are interpreted . All toothed whales are opportunistic , meaning they will eat anything they can fit in their throat because they are unable to chew . These animals rely on their well @-@ developed flippers and tail fin to propel themselves through the water ; they swim by moving their fore @-@ flippers and tail fin up and down . Whale ribs loosely articulate with their thoracic vertebrae at the proximal end , but they do not form a rigid rib cage . This adaptation allows the chest to compress during deep dives as opposed to resisting the force of water pressure . Excluding dolphins and porpoises , odontocetes consist of four families : belugas and narwhals ( monodontids ) , sperm whales ( <unk> ) , dwarf and pygmy sperm whales ( <unk> ) , and beaked whales ( ziphiids ) . There are six species , sometimes referred to as " blackfish " , that are dolphins commonly misconceived as whales : the killer whale , the melon @-@ headed whale , the pygmy killer whale , the false killer whale , and the two species of pilot whales , all of which are classified under the family Delphinidae ( oceanic dolphins ) . 
