 The caudal fin is <unk> , meaning the upper and lower lobes are about equal in size . The spine ends at the caudal peduncle , the base of the caudal fin , distinguishing this group from those in which the spine extends into the upper lobe of the caudal fin , such as most fish from the Paleozoic ( 541 to 252 million years ago ) . The neural arches are elongated to form <unk> which provide support for this upper lobe . In addition , the hypurals , bones that form a flattened plate at the posterior end of the vertebral column , are enlarged providing further support for the caudal fin . In general , teleosts tend to be quicker and more flexible than more basal bony fishes . Their skeletal structure has evolved towards greater lightness . While teleost bones are well calcified , they are constructed from a scaffolding of struts , rather than the dense cancellous bones of <unk> fish . In addition , the lower jaw of the teleost is reduced to just three bones ; the dentary , the angular bone and the articular bone . 
