Teeth of vertebrates are under constant use and therefore show wear-induced traces on the surface. According to Williams (2005), the mechanism by which wear occurs is a mechanical and/or chemical process resulting in material loss. Wear facets, the smooth and polished contact areas between opposing teeth, form during force-fit chewing activity between antagonists due to attritional (tooth-tooth) and abrasional (tooth-substrate-tooth) contacts involving either some kind of resistant alimentary bolus or some other dental behavior with an empty mouth cavity (Maier & Schneck 1981). In mammals, the occlusion of dental surfaces produces characteristic facet patterns on the crown’s surface. Orientation and inclination of a facet are determined by tooth morphology, while the texture of the surface (e. g., complexity and roughness) is the result of the food ingested (e. g., Schulz et al. 2010, Winkler et al. 2019, Schulz-Kornas et al. 2020, this volume). Complementary patterns of wear facets on the occlusal surface of opposing teeth change in shape and size during ontogeny and therefore can be used for age determination (e. g., Baumann 1949, Grau et al. 1970, Habermehl 1985, Anders et al. 2011a,b, Ruf et al. 2020, this volume). Wear facet patterns begin to form as soon as the tooth crown erupts and antagonists occlude. Fortelius (1985) differentiated between primary and secondary occlusal surfaces. Facets on primary surfaces develop gradually on the enamel cover (i. e., enamel facets) and only later expose the dentin with increasing wear due to age. In those cases, the exposed dentin has no explicit function. Facets on a secondary surface are composed of enamel and dentin. Dentin exposure happens relatively fast and it forms depressions in close proximity to protruding enamel, and the combination of both has a specific function. Those facets remain constant for a relatively long period of time in the life of an animal (i. e., dentin facets interrupted and/ or surrounded by enamel bands). Facets on secondary surfaces are specialized occlusal surfaces that are mostly developed in herbivorous taxa with a horizontal power stroke movement, regardless of the direction (Koenigswald 2020, this volume). In these specialized cases enamel and exposed dentin function as a unit, and neighboring facets merge and may cover large areas composed of both tissues (e. g., occlusal surface of elephant molars). In correspondence, some mammal groups developed specialized dentitions (e. g., hypsodonty, euhypsodonty, A new wear facet terminology for mammalian dentitions

Mammal teeth have evolved morphologies that allow for the efficient mechanical processing of different foods, therefore increasing dietary energy uptake for maintenance of high metabolic demands. However, individuals masticate foods with biomechanical properties at odds with the optimal function of a given tooth morphology. Here, we investigate tooth form and function using two quantitative 3D methods at different scales on the same individuals of nine bovid species. Dental topometry quantifies the gross morphology, and therefore, reflects evolutionary adaptive patterns. Surface texture analysis infers mechanical occlusal events, which reflect the actual tooth function, and is free from the influence of morphology. We found that tough foods can be satisfactorily exploited by grazing species with enamel ridge morphologies not more complex than those found in intermediate feeders and browsers. Thus, the evolution of enamel complexity is likely determined by a balance between adaptation and constraints. Wider enamel ridges seem to be a common functional trait in bovids to compensate for severe wear from abrasive foods and/or chipping from hard foods. Our results demonstrate that supposedly essential functional adaptations in tooth morphology may not be required to process food efficiently. This emphasizes the large plasticity between “optimal” morphology and the potential function of the tooth, and underscores the need to appreciate (apparently) maladaptive structures in mammalian evolution as nevertheless effective functioning units.

ABSTRACT Plasticity of tooth shape in mammals is of great adaptive value for the efficient exploitation of specific feeding niches and is a crucial mechanism for ecological diversification. In this study, we aimed to infer chewing effectiveness from the functional shape of different postcanine teeth within bovids, the most diverse extant group of large herbivorous mammals. We consider the postcanine dentition as a masticatory unit and test for differences related to food biomechanical properties, dietary abrasiveness, and chewing dynamics. We compare functional properties of the postcanine tooth row among species with well‐known dietary strategies by integrating digitalization of high‐resolution occlusal surface 3D‐models of upper postcanine dentitions and quantification of the indentation index ( D ), a structural parameter representing enamel complexity. We test for differences in the occlusal shape among tooth positions in the postcanine dentition using robust, heteroscedastic tests in a one‐way analysis of variance. Our results show three distinct patterns of enamel complexity along the tooth row: (1) D is more homogeneously distributed among tooth positions; (2) D increases gradually in the mesiodistal axis along the tooth row; and (3) D increases abruptly only at the transition between premolars and molars. We interpreted these patterns as different adaptive configurations of the postcanine tooth row relating to diet. Grass‐ and fruit‐eating bovids show the same abrupt increase in enamel complexity at the transition from premolars to molars. Intermediate feeding and leaf‐browsing species show the same gradual, mesiodistal increase in complexity along the tooth row. The absolute physical dietary resistance (biomechanical properties plus abrasiveness) and its relation to mechanical constraints of the chewing stroke are the likely selective factors leading to convergence of enamel complexity patterns along the tooth row among taxa with different diets. J. Morphol. 275:328–341, 2014. © 2013 Wiley Periodicals, Inc.

Evolution in isolated island has shaped a variety of endemic taxa with outstanding characteristics. Amongst them is the extinct bovid genus Myotragus, endemic to Mallorca and Menorca Island, for which six succeeding species have been described: M. palomboi, M. pepgonellae, M. antiquus, M. kopperi, M. batei and M. balearicus. Myotragus has developed special cranial and post-cranial adaptations to meet the specific ecological demands of its insular habitat, like progressive dwarfing and fused limb elements. During its evolution, the dentition of Myotragus underwent subsequent changes: firstly a reduction in the number of teeth, and secondly an increase in hypsodonty. The ecological conditions inducing this dental evolution, especially Myotragus' diet, remain unknown. In this study, methods of 3D-dental topometry, enamel surface texture analysis according to ISO/FDIS 25178-2, and Scale-Sensitive Fractal Analysis (SSFA) are applied in order to infer palaeodiets of M. pepgonellae, M. kopperi, M. batei and M. balearicus, and to test the hypothesis that a dietary change may have occurred in the Myotragus lineage which relates to gradual morphological changes on upper second molars. We detect changes in the enamel/dentin ratio, enamel ridge length and enamel surface area within the lineage. Furthermore, Myotragus balearicus has enamel surface texture characteristics also present in extant browsing ungulates, while the three antecedent Myotragus species show an enamel surface texture signal similar to extant grazers. These results suggest a dietary change and are interpreted as a successive adaptation to limited resources in an isolated, insular environment. They can either be a consequence of a change in plant community structure or a successive expansion of Myotragus' dietary range due to increased intraspecific competition. (C) 2013 Elsevier Masson SAS. All rights reserved.

Newly colonised, isolated habitats, like islands, provide diverse niches to be filled and are prone to facilitate ecological separation which might lead to an adaptive radiation. Examples of such radiations can be found in the Mediterranean for the genera Candiacervus (Crete), Nesogoral (Sardinia) and Hoplitomeryx (Gargano). A different strategy to cope with limited resources on islands is generalism. We test whether populations of the endemic bovid Myotragus balearicus from two sites and Pleistocene as well as Holocene levels on Mallorca island displays ecological separation indicated by diet, or whether the species shifted its dietary trait towards generalism. We expect to find either: (1) dietary divergence in space and time (between sites and stratigraphic levels), which would indicate niche partitioning and/or a shift in dietary traits due to environmental influences; or (2) dietary congruence in a less specialised, generalistic dietary strategy in space and time which would indicate a flexible trait to cope with instable resource availability. We compare individuals from a fossil assemblage at a northern site and one assemblage from the eastern coast in terms of their dietary traits. Traits are reconstructed using dental dietary proxies, complementary in time scale and resolution. (1) 3D-dental topometry and (2) enamel surface texture analysis. Data suggest that individuals from both assemblages of M. balearicus behaved as variable browse dominated intermediate feeders. We thus conclude that the observed variability relates to a shift towards generalism as a subsistence strategy. We consider hypsodonty the pre-adaptation for this life style that enabled M. balearicus to exploit almost any food source in its energetically restricted island habitat.