Hearing is a wonderful thing, able to translate vibrations of air into sound. Numerous desert creatures rely on sound more than on sight, for many are nocturnal, only active during the dark hours. Part of the great sensitivity in mammals is due to the three small bones in our middle ears, the auditory ossicles. These transmit and amplify the vibrations of the ear drum, conveying them to the inner ear.
What's fascinating from an evolutionary viewpoint is their origins.
Studies of embryos and fossils trace their origin far back in time. The ossicle next to
the inner ear, the stapes, can be traced back to part of a gill arch in a very distant
fish ancestor. The other two ossicles, the malleus and incus, are derived from bones
that, in our reptilian ancestry, formed the joint between skull and lower jaw, as they
do today in modern reptiles. After incipient mammals evolved a new jaw joint, those
bones were in perfect position to be incorporated into a hearing device in
evolution's favorite avenue—jury-rigging structures for new roles.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.