The secrets of the inner ear

Peel back your skin & muscles and peer past your skull and you’d find three very important little semi-circular canals that make up your inner ear. These canals control your balance and aide in motion – and are the key to Brian Shearer, Elise, and Diana’s investigation of extant and extinct primate locomotion.

A micro-CT scanner allows you to penetrate a skull (and other things) without the very invasive and destructive process of physically opening up a skull. X-ray light is bombarded at the specimen. Bones reflect these x-rays differently according to their density, a phenomenon that allows for the creation of a three dimensional computer model. With this model or 3-D scan, bones are differentiated based on their density.

Elise and Diana

In their search for the semi-circular canal, Elise and Diana slowly e-dissolve their 3-D skull models leaving behind only the densest bones:  ghostly teeth and the petrous, one of the densest bones in the human body and the bone that supports the semicircular canals.

Once located, Elise and Diana, start the process of rendering or digitizing the canals. Going layer-by-layer in this 3-D model they trace the canals’ outline and contours. When completed, the team will measure the size, volume, and the orientation of each canal, metrics that correlate with modes of primate location. For example, more perpendicular angle of orientation is associated with faster swinging in primates know for their brachiation (aka arm swinging locomotion). 

The team hopes to explore the form of these semi-circular canals in both juveniles and adults across several extant (living) primates. In the end, better understanding the relationship between the form of the semicircular canals and locomotion in extant species may help paleontologist understand how extinct primates got around – simply by looking to its inner ear.

Brian Shearer, primatologist, biological anthropologist, mentor