Bone‐conduction hearing and seismic sensitivity of the late permian anomodontKawingasaurus fossilis

Abstract

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.

Reconstructing the Auditory Apparatus of Therapsids by Means of Neutron Tomography

“…This might be also the reason that neutron radiation produces usually a good contrast between fossil bones and matrix (Laaß et al 2010), which is probably caused by hydrogen-containing minerals in fossil bones such as Hydroxyl-Apatite. Neutron tomography was already successfully used, for example, for the examination of sauropod vertebrae and ribs (Schwarz et al 2005), archosaurian reptile bones (Cisneros et al 2010) and therapsid skulls (Laaß et al 2010;Laaß 2014).…”

Neutron Imaging in Cultural Heritage Research at the FRM II Reactor of the Heinz Maier-Leibnitz Center

“…The latter consists of two components: the vestibule for hearing and the semicircular canals for equilibrium. Remarkably, the vestibule of D. feliceps does not show a distinct cochlear cavity (Figure 8c,d, which is otherwise already present in some advanced therapsids and in mammals and might be an indication for a low sensitivity to airborne sound [13,14]. …”

“…Recent cold neutron tomography of small therapsids skulls performed at ANTARES supported the hypothesis that a bony plate at the lower jaw of therapsids, the reflected lamina, served for sound detection [13]. A reflected lamina was also present at the lower jaw of S. potens, but it was extremely large and thick in comparison to small species.…”

“…The latter consists of two components: the vestibule for hearing and the semicircular canals for equilibrium. Remarkably, the vestibule of D. felicepsdoes not show a distinct cochlear cavity (Figure 8c,d, which is otherwise already present in some advanced therapsids and in mammals and might be an indication for a low sensitivity to airborne sound [13,14]. In mandibular specimens (a), due to fossilization, we sometimes obtained noisy datasets (b), but it was still possible to retrieve reliable morphological information on the internal tooth structure (c) [11] (with permission).…”

Morphological evolution of the mammalian jaw adductor complex

“…Digital techniques have been used to visualise and reconstruct synapsid soft-tissue features, such as the nasal anatomy and the olfactory apparatus (Laaß et al, 2011;Ruf et al, 2014), the endocranial anatomy (Rowe et al, 2011; and inner ear morphology (Rodrigues, Ruf & Schultz, 2013;Laaß, 2015Laaß, , 2016. Functional studies, involving digital visualisation, computational biomechanical approaches and three-dimensional free body analyses have employed the vector-based representation of adductor musculature (Gill et al, 2014;Jasinoski, Abdala & Fernandez, 2015;Reed et al, 2016).…”