The ability of the tympanum and stapes to effectively transmit vibrations is called impedance matching . Early tetrapods like temnospondyls 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 temnospondyls like Dendrerpeton could not hear airborne sound but would have been able to detect vibration in the ground . Later temnospondyls like Doleserpeton had otic regions adapted to hearing . Doleserpeton has a structure in the inner ear called the perilymphatic 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 Doleserpeton and related temnospondyls was able to detect airborne sound and may have been ancestral to that of living amphibians .