Abstract
Dental microwear of four postcanine teeth of Exaeretodon argentinus was analyzed using both two dimensional (2D) and three dimensional (3D) methods to infer their masticatory jaw movements. Results of both methods were congruent, showing that linear microwear features (scratches) were well aligned and mostly directed to the antero-posterior direction in all four teeth examined. These findings support the palinal masticatory jaw movement, which was inferred in previous studies based on the observation of gross morphology of wear facets. In contrast, the lack of detection of lateral scratches confirmed the absence of the lateral jaw movement that was also proposed by a previous study. Considering previous microwear studies on cynodonts, palinal jaw movements observed in Exaeretodon evolved within cynognathian cynodonts from the fully orthal jaw movement of its basal member. Although there are currently only three studies of dental microwear of non-mammalian cynodonts including the present study, microwear analysis is a useful tool for the reconstruction of masticatory jaw movement and its future application to various cynodonts will shed light on the evolutionary process of jaw movement towards the mammalian condition in more detail.
Highlights
Evolution of postcanine occlusal pattern and masticatory jaw movement toward the mammalian condition among cynodonts has been studied intensively as one of the historical topics in vertebrate paleontology [1,2,3]
Mean orientations of the scratches were within 15 degrees from the anterior direction (90 degrees) for postcanines of PVSJ 1091 and 702, and within 20 degrees for the postcanine of PVSJ 707
The 3D surface texture parameter Str recorded the lowest value in PVSJ 1091 and the highest in PVSJ 707
Summary
Evolution of postcanine occlusal pattern and masticatory jaw movement toward the mammalian condition among cynodonts has been studied intensively as one of the historical topics in vertebrate paleontology [1,2,3]. Masticatory jaw movements of cynodonts had been considered to have some phylogenetic significance; for example, palinal (i.e., backward) movement of the mandible of traversodontids and tritylodontids was considered evidence of their ancestor-descendant relationship [2]. Jaw movement of Exaeretodon argentinus advances in understanding of the phylogeny of cynodonts [4], it is considered that various jaw movement patterns of cynodonts were evolved as an adaptation for various diets. Palinal jaw movements were perhaps adaptations for an herbivorous diet, which evolved independently among traversodontids and tritylodontids, and within mammaliaforms among haramiyidans and multituberculates [3]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
