The 3D topography of dental tools: food item mechanical properties and primate dentition morpho-functional evolution – DieT-PrimE

Mechanically challenging foods are hypothesized to play a major role in dental adaptation. Generally speaking, these foods are broken into two categories: preferred and fallback foods (FBFs). Preferred foods are those consumed when all food resources are available, while fallback foods are those are consumed in lieu of preferential foods, frequently because of seasonal variation in resources. The aim of DieT-PrimE is to assess if primate dental occlusal morphology is wholly or partially adapted to i) mechanically challenging preferred-foods. ii) Mechanically challenging FBFs iii) or the most mechanically challenging foods, regardless if they are preferred or fallback. This is fundamental for understanding the emergence, selection and fixation of dental novelties, a major issue in paleoprimatology.
DieT-PrimE postulates that primate teeth bear “dental tools” representing functional, morphological adaptations to mechanically challenging foods. We believe these critical traits can be quantified using our topographic signifiers, which constitutes the core of our project. Following in the DieT-PrimE project, we will use a form-function approach to investigate the relationship between diet, dietary mechanical properties, and dental tools. First, the diets of 20 key extant primates will be established to determine their preferred and fallback foods. The mechanical properties of these foods (food mechanical properties, FMPs) will be gathered in lab or on the field using an universal tester to identify the most challenging food items consumed by those species. These properties will include hardness (resistance to surface indentation) and toughness (resistance to fracture propagation). Hardness will be used as a proxy for resistance to fracture initiation.
While gathering FMPs, we will review aspects of dental morphology suggested to facilitate fracture initiation and propagation (e.g. cusp sharpness) during mastication. Our project aims to quantify these aspects of dental morphology using an innovative analytical method, 3D Dental-Topography. Dental topography is the quantification of tooth shape with a single metric using geographic information systems (GIS) technology, but has since expanded to use non-GIS specific technologies and metrics and has been used to quantify singular aspects of dental form. Dental topography will be used to quantify aspects of tooth shape such as inclination, orientation, mean curvature, relief, and complexity, and additionally quantify a metric important for tooth strength, enamel thickness. Dental topographic metrics will be developed to finely characterize individual dental phenotypes. These phenotypes will be compared to simplified, theoretical, dental models with similar phenotypes and known masticatory performance. A standalone program will additionally be created to provide the scientific community with a user-friendly way of (semi)automatic detection and quantification of dental tools in extant and extinct primates.
The relationship between dental tool geometries and FMPs will be achieved through complex statistical analyses and mechanical testing, using a chewing simulator and a universal tester equipped with 3D-printed dental models. This step will allow to better test our hypotheses concerning the relationship between dental form and function in each primate species, and determine whether each species dental form is compliant with the expected function(s) to process its preferred and fallback food items.
Using fossil taxa, our project will ultimately allow for identifying which dental features have been selected for in Primates and the role of dietary constrains on these morphologies. We will, for instance, focus on the emergence of key dental features, such as the bunodonty in Anthropoidea, bilophodonty in Cercopithecoidea, and peculiar morphologies such as the thick-enameled molars of the australopith Paranthropus.