Left endosseous labyrinths of the aquatic, flightless Great Auk <i>Pinguinus impennis</i> (A) and the terrestrial foraging, volant Killdeer <i>Charadrius vociferus</i> (B) in lateral view (not to scale for comparison).

<p>Note the differences in the orientation of the labyrinths (based on horizontal semicircular canal), compression of the semicircular canals (i.e., elliptical versus rounded shape), overall thickness of canals, curvature of the cochlear duct, shape of the distal end of the cochlear duct, and participation of the anterior semicircular canal in the common crus.