Investigating the dental toolkit of primates based on food mechanical properties: Feeding action does matter

Abstract

Although conveying an indisputable morphological and behavioral signal, traditional dietary categories such as frugivorous or folivorous tend to group a wide range of food mechanical properties together. Because food/tooth interactions are mostly mechanical, it seems relevant to investigate the dental morphology of primates based on mechanical categories. However, existing mechanical categories classify food by its properties but cannot be used as factors to classify primate dietary habits. This comes from the fact that one primate species might be adapted to a wide range of food mechanical properties. To tackle this issue, what follows is an original framework based on action-related categories. The proposal here is to classify extant primates based on the range of food mechanical properties they can process through one given action. The resulting categories can be used as factors to investigate the dental tools available to primates. Furthermore, cracking, grinding, and shearing categories assigned depending on the hardness and the toughness of food are shown to be supported by morphological data (3D relative enamel thickness) and topographic data (relief index, occlusal complexity, and Dirichlet normal energy). Inferring food mechanical properties from dental morphology is especially relevant for the study of extinct primates, which are mainly documented by dental remains. Hence, we use action-related categories to investigate the molar morphology of an extinct colobine monkey Mesopithecus pentelicus from the Miocene of Pikermi, Greece. Action-related categories show contrasting results compared with classical categories and give us new insights into the dietary adaptations of this extinct primate. Finally, we provide some possible directions for future research aiming to test action-related categories. In particular, we suggest acquiring more data on mechanically challenging fallback foods and advocate the use of other food mechanical properties such as abrasiveness. The development of new action-related dental metrics is also crucial for primate dental studies.

Dental topography and the diet of Homo naledi

“…Besides inferring dietary ecology, dental topography has also been used to predict enamel surface morphology from the shape of the enamel-dentine junction (Skinner et al, 2010;Guy et al, 2015), to investigate evolutionary pressures, such as niche partitioning (Boyer et al, 2012;Godfrey et al, 2012;Berthaume and Schroer, 2017), and to describe and assign a primate fossil to a new species (Boyer et al, 2012). The relationship between tooth shape and food item breakdown have additionally been investigated (Thiery et al, 2017a(Thiery et al, , 2017b, but how foods break down during mastication is not yet fully understood, and the proposed categories (e.g., crushing, grinding) need to be better defined from a fracture mechanics standpoint before this classification system can be used (Berthaume, 2016b;Thiery et al, 2017b).…”

Beyond the Map: Enamel Distribution Characterized from 3D Dental Topography

“…Nonetheless, a feature that was not taken into account is the feeding action performed to access or process stress-limited food, which needs to be considered when evaluating the form-function relationship between diet and dental morphology (Thiery et al, 2017). For instance, P. pithecia does not crack open the most challenging food it consumes with its molars, but with its strong and proclive incisors and canines (Kinzey and Norconk, 1993; Norconk and Veres, 2011).…”

“…When possible, they were also classified as stress-limited or soft food eaters sensu Lucas et al (2000). To do so, we followed the methodology presented in Thiery et al (2017) and combined reports of dietary composition, including seasonal variation in food item consumption, with studies on the physical properties of primates food. Whenever a species was reported to consume stress-limited food on a regular basis, we classified it as a hard food eater .…”

Overcoming sampling issues in dental tribology: Insights from an experimentation on sheep

“…These qualitative terms are used to broadly qualify the food properties used in this study. Grasses are considered tougher, i.e., to have a higher energy release rate (Berthaume, 2016;Thiery et al, 2017) than browse such as clover. However, we should note that the clover and grass assemblages foraged by the ewes during the experiments do not display any significant differences in fracture toughness (meaning the ability to absorb deformation energy per unit volume before failure) measured thanks to a tensile test (Merceron et al, 2016).…”