Postcanine tooth function and jaw movement in the gomphodont cynodont Diademodon (Reptilia; Therapsida)

Abstract

The postcanine dentition of Diademodon was well adapted, in both morphology and pattern of replacement, to exercising and maintaining precise occlusion. These teeth may be grouped into three morphological classes, consisting of conical, gomphodont and sectorial teeth. The anterior conicals may have acted as gripping teeth, and the posterior sectorials may have been utilized as food "tenderizers" or shredders, while the intermediate gomphodont teeth were utilized in the mastication of food items. The gomphodont teeth, which show evidence of heavy wear, were examined in the scanning electron microscope (SEM), in order to attempt a reconstruction of the masticatory jaw movements in this animal, based on the morphology and orientation of the occlusal wear facets. The occlusal surfaces of the gomphodont teeth are pitted. The pitted occlusal surface texture is an indication of either abrasion or attrition, resulting from direct pounding of the lower teeth against their maxillary antagonists. It is concluded that masticatory jaw movements in Diademodon were wholly orthal. There is no dental evidence to support the contention that this reptile exercised either propalinal (Hopson, 1971) or ectental chewing movements. The jaw closing action in Diademodon appears to have been equivalent to the masticatory power stroke.