The inner ear bones of mammals have evolved from

bones that form the jaws of reptiles.

auditory ossicles

Explanation:

In reptiles, the eardrum is connected to the inner ear via a single bone, the columella, while the upper and lower jaws contain several bones not found in mammals. Over the course of the evolution of mammals, one bone from the lower and one from the upper jaw (the articular and quadrate bones) lost their purpose in the jaw joint and were put to new use in the middle ear, connecting to the existing stapes bone and forming a chain of three bones, the ossicles, which transmit sounds more efficiently