Columella (auditory system)

The columella form thin, bony structures in the interior of the skull and serve the purpose of transmitting sounds from the eardrum.

Under selective pressure to detect airborne sound vibrations, the columella in crocodilians have become more slender and reduce their mass.

[6] Birds and modern crocodilians have evolved a trifurcated columella, which forms a Y-shaped support structure on the surface of the tympanic membrane.

[7] In birds, this is thought to increase the surface area of the columellar footplate, thus lowering the threshold of hearing and improving the detection of airborne sound waves.

[3] In reptiles, the columella function to transduce sound through the middle ear as part of the auditory pathway.

[3] Due to the rigid bony structure, the columella primarily responds to low-frequency vibrations transmitted through the ground.

[3] In Amphisbaenia, the extracolumella is particularly lengthened and firmly connects with a layer of skin over dentary bone of the lower jaw.

As a result, the amphisbaenian is able to detect substrate vibrations as it burrows through the ground while protecting the internal ear from damage.

This is thought to provide a lever advantage in conducting airborne sound from the distal to the proximal end of the columella.

Later-arising reptiles with columella likely evolved stronger limbs and a more crawling posture, which removed the body from the ground and prevented the transmission of ground-conducted sounds.