Absence of the Articular Disc in the Tasmanian Devil Temporomandibular Joint

The articular disc of the temporomandibular joint is a constant structure in mammals. According to Parsons' report in 1900, however, it is absent in four animals: the armadillo, two kinds of monotremes and the Tasmanian devil. Thereafter, no research was performed to confirm this observation. The aim of this study was to determine by anatomical and histological examination whether the Tasmanian devil has an articular disc in its temporomandibular joint. Six fresh frozen corpses and one dry skull of Tasmanian devils were obtained from the School of Zoology, University of Tasmania. The corpses were dissected and the morphology of the temporomandibular joint was carefully observed by gross anatomical and histological examination. The structure of the temporomandibular joint of the dry skull was examined macroscopically and by micro-computed tomography. In all cases, absence of the articular disc in the Tasmanian devil temporomandibular joint was morphologically confirmed. The surface layer of both the condyle and the glenoid fossa comprised a thick fibrous tissue. Micro-computed tomography revealed dense and fine trabecular bone in the condyle. The thick fibrous tissue covering the condyle and high-density trabecular bone in the condyle might play a role in absorption against powerful mastication and heavy loading of the Tasmanian devil temporomandibular joint.