Measurements of the middle and external ear (A) and ear ossicles (B). A and B are not drawn to the same scale. A is based on the CT images of Cranium 5. V_MA, volume of the mastoid antrum and connected mastoid air cells, measured from its limit with the aditus ad antrum (dotted line 1); V_AD, volume of the aditus ad antrum, measured from its limit with the middle ear (dotted line 2) to its limit with the mastoid antrum (dotted line 1); V_MEC, volume of the middle ear cavity measured from its limit with the aditus ad antrum (dotted line 2) to the edge of the tympanic groove (dotted line 3); L_AD, length of the aditus ad antrum, measured as the mean distance from its limit with the middle ear cavity to the entrance to the mastoid antrum; L_EAC, length of the external auditory canal, measured from the superior point of the tympanic groove to the spina suprameatum. Dotted line 4 marks the level at which the cross-sectional area of the external auditory canal (A_EAC) was measured. B is based on the profiles of the malleus and incus from the temporal bone AT-1907 and the stapes from Cranium 5. L_M, functional length of the malleus, measured as the maximum length from the superior border of the short process to the inferior-most tip of the manubrium; L_I, functional length of the incus measured from the lateral-most point along the articular facet to the lowest point along the long crus; A_FP, measured area of the footplate of the stapes.

Sound power (dB) at the entrance to the cochlea relative to P₀ = 10^-18 W for an incident plane wave intensity of 10^-12 W/m². All individuals have been modeled by using the model defined by Rosowski (17) and the cochlear input impedance (Z_c) of Aibara et al. (27). Solid blue line, modern human; solid green line, chimpanzee 3D CT; solid black line, theoretical chimpanzee-like modern human individual; dashed black line, theoretical human-like chimpanzee individual. solid red line, AT-84; dashed red line, AT-4103; dashed-dotted red line, Cranium 5; solid magenta line, AT-421; dashed magenta line, AT-1907.

Sound power (dB) at the entrance to the cochlea relative to P₀ = 10^-18 W for an incident plane wave intensity of 10^-12 W/m². Results from modern human (solid line) and chimpanzee (dashed line) individuals are shown and were obtained by using the model defined by Rosowski (17) and the cochlear input impedance (Z_c) of Aibara et al. (27). Chimpanzee individual is based on the 3D CT reconstruction.