 The ability of the tympanum and stapes to effectively transmit vibrations is called impedance matching . Early tetrapods like <unk> have thick stapes with poor impedance matching , so it is now thought that they were not used for hearing . Instead , these thick stapes may have functioned to support the tissue that covers the otic notch . Early <unk> like <unk> could not hear airborne sound but would have been able to detect vibration in the ground . Later <unk> like <unk> had otic regions adapted to hearing . <unk> has a structure in the inner ear called the <unk> duct , which is also seen in frogs and is associated with hearing . Its stapes is also a better transmitter of sound . The hearing system of <unk> and related <unk> was able to detect airborne sound and may have been ancestral to that of living amphibians . 
