Kelsey Stilson, Postdoctoral Research Associate, Ecology, Evolution, and Organismal Biology
Abstract Title: How Do You Chew with Half a Mandible?
Abstract: The Virginian Opossum (‘Didelphis virginiana’) is the only native North American marsupial. They are notorious for their ability to eat anything from insects, dead larger animals, plants, or anything from a garbage bin. Despite their unique lack of dietary preferences and evolutionary history, they are the same as the majority of Mammalia in at least one key morphological feature: an unfused mandibular symphysis. This means that each side of the jaw moves semi-independently from the other and is connected at the front by a fibrous ligament. However, the hemimandibular system has yet to be fully described and tested using modern techniques. We used biplanar videoradiography and the X-Ray Reconstruction of Moving Morphology pipeline to measure bilateral hemimandibular kinematics in five ‘D. virginiana’ individuals before and after transection of the left inferior alveolar nerve (IAN), which gives feeling to the left lower tooth row. Results in non-transected individuals show that, during occlusion, there is limited hemimandibular movement anteriorly due to the interlocking canines. However, the temporomandibular joint is highly mobile. We hypothesize that this mobility allows for the complex occlusal movements necessary for an interlocking molar system. Left IAN transection impacted jaw rotation and translation of both and left and right hemimandibles during the occlusal phases of the gape cycle. Importantly, this demonstrates that a one-sided nerve transection changes the kinematics of both hemimandibles, and suggesting that bilateral periodontal afferent feedback is necessary for integration in the brainstem and use for efficient mastication.