 <unk> and all other living <unk> have a rod @-@ like bone called the <unk> that aids in hearing by transferring <unk> from the ear drum — or <unk> <unk> — to the inner ear . <unk> also have a <unk> , which projects into the <unk> cavity . The <unk> likely evolved from the <unk> of lobe @-@ <unk> fishes . The positioning of the <unk> and the shape of the <unk> region suggests that the <unk> of <unk> and frogs are <unk> , but the <unk> of these amphibians are no longer considered <unk> with the hearing systems of reptiles , birds , and mammals . Therefore , ear structures in <unk> were not ancestral to those of all other <unk> . 
