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Burrowing Permian anomodont Kawingasaurus seismic sound hearing ability

Ben Creisler

A new online paper:

Michael Laaß (2014)
Bone-conduction hearing and seismic sensitivity of the late Permian
anomodont Kawingasaurus fossilis.
Journal of Morphology (advance online publication)
DOI: 10.1002/jmor.20325

An investigation of the internal cranial anatomy of the anomodont
Kawingasaurus from the Upper Permian Usili Formation in Tanzania by
means of neutron tomography revealed an unusual inner and middle ear
anatomy such as extraordinarily inflated vestibules, lateroventrally
orientated stapes with large footplates, and a small angle between the
planes of the anterior and lateral semicircular canals. The vestibule
has a volume, which is about 25 times larger than the human vestibule,
although Kawingasaurus has only a skull length of approximately 40 mm.
Vestibule inflation and enlarged stapes footplates are thought to be
functionally correlated with bone-conduction hearing; both
morphologies have been observed in fossorial vertebrates using seismic
signals for communication. The firmly fused triangular head with
spatulate snout was probably used for digging and preadapted to
seismic signal detection. The quadrate-quadratojugal complex was able
to transmit sound from the articular to the stapes by small vibrations
of the quadrate process, which formed a ball and socket joint with the
squamosal. Mechanical considerations suggest that the ventrolaterally
orientated stapes of Kawingasaurus was mechanically better suited to
transmit seismic sound from the ground to the fenestra vestibuli than
a horizontal orientated stapes. The low sound pressure level
transformer ratio of 2–3 in Kawingasaurus points to a seismic
sensitivity of the middle ear and a vestigial or reduced sensitivity
to airborne sound. Three hypothetical pathways of bone conduction in
Kawingasaurus are discussed: 1) sound transmission via the spatulate
snout and skull roof to the otic capsules, 2) relative movements
resulting from the inertia of the mandible if sound is percepted with
the skull, and 3) bone conduction from the substrate via mandible, jaw
articulation, and stapes to the inner ear.