In crown reptiles, the stapes is a slender bone capable of transmitting high-frequency sounds from the outer tympanum to the inner ear. However, this element is larger and more robust in stem-group and early crown amniotes. In those taxa it likely played a greater role in structural support of the cranium than in transmitting sound. The early amniote stapes has been suggested to have been capable at most of transmitting low frequency sounds. This, in conjunction with quadrate morphology, caused previous workers to categorize stem and crown reptiles in a binary manner when discussing the evolution of hearing: impedance-matching or not. This binary classification implies a rapid transition between states. There is, however, a paucity of transitional fossil stapedes; our understanding of the evolutionary transition from low-frequency to high-frequency hearing in reptiles is limited. Our discovery of stapedes in near-crown stem-reptiles suggests that the evolution of this trait was not as binary as previously implied. The stapedes of two archaic diapsid stem-reptiles, Palacrodon sp. and Avicranium renestoi, are minute elements that show a transitional morphology between the robust, supportive stapedes of earlier stem-reptiles and the slender, elongate morphology of crown reptiles. Moreover, we find that the stapes of Youngina capensis, one of the most crownward stem-reptiles, is much more elongate than those of earlier stem-reptiles, despite frequently having been described as robust. The stapedial morphologies of these taxa suggest they were capable of hearing higher frequencies than more basal taxa. We posit therefore that stapedial evolution was more gradual than previously appreciated, and that middle ear specializations for higher-pitched hearing may have preceded external ear (tympano-quadrate) specializations.