Bite force and gape are two important performance metrics of the feeding system, and these metrics are inversely related for a given muscle size because of fundamental constraints in sarcomere length-tension relationships. How these competing performance metrics change in developing primates is largely unknown. Here we quantify in vivo bite forces and gapes across ontogeny and examine these data in relation to body mass and cranial measurements in captive tufted capuchins, Sapajus spp. Bite forces and gapes were also compared across geometric and mechanical properties of mechanically challenging foods to investigate relationships between bite forces, gapes, and food accessibility (defined here as the ability to breach shelled nuts). Bite forces at a range of gapes and feeding behavioral data were collected from a cross-sectional ontogenetic series of 20 captive and semi-wild tufted capuchins at the Núcleo de Procriação de Macacos-Prego Research Center in Araçatuba, Brazil. These data were paired with body mass, photogrammetric measures of jaw length and facial width, and food geometric and material properties. Tufted capuchins with larger body masses had absolutely higher in vivo bite forces and gapes, and animals with wider faces had absolutely higher bite forces. Bite forces and gapes were significantly smaller in juveniles compared to subadults and adults. These are the first primate data to empirically demonstrate the gapes at which maximum active bite force is generated and to demonstrate relationships to food accessibility. These data advance our understanding of how primates meet the changing performance demands of the feeding system during development.

Nerves providing sensation to the lower face and jaw exit the mandibular canal via the mental foramen. In humans, there are many documented occurrences of additional foramina (accessory mental foramina, AMFs) on the lateral mandibular surface that may also contain nervous structures. There are large discrepancies in the literature regarding how often AMFs occur in humans, and investigations of non-human hominoid AMFs are rare. Consequently, the causes of interspecific diversity in this variable have not been explored. This project seeks to compare the frequency and number of AMFs between males and females, and among human regional groups and hominoid subspecies and species, and to investigate possible causal factors for any differences identified. No significant differences were found between males and females in any group. Gorillas and orangutans had the highest percentages of individuals with AMFs and the highest mean number of foramina, while modern humans and siamangs had the lowest figures for these variables. Significant differences (p < .05) were found for the mean number of foramina between most pairs of species. The results also showed that species with mandibles that are larger overall, have a larger area anterior to mental foramen, and a longer mandibular canal typically present more AMFs. The strongest correlation was found between the mean number of mental foramina and mandibular canal length. We suggest that these results provide preliminary support for the hypothesis that increasing mandibular canal length increases the likelihood that that nerves will ramify, leading to greater frequencies of accessory mental foramina.

With increased tablet ownership in the United States comes increased levels of neck flexion compared to desktop or laptop computer use, and these neck postures have been linked to increases in neck pain. Importantly, tablet viewing postures can be achieved in multiple ways and could be determined by the morphology of the individual and/or other extraneous factors. In this study, we aim to preliminarily evaluate how neck postures vary during tablet use among individuals and link this variation to other factors such as sex, height, weight, presence/absence of temporomandibular joint disorder (TMD), and morphology of the head and neck. We analyzed two-dimensional landmarks placed on lateralview radiographs of 22 participants (10 female and 12 male) seated in neutral, upright, fully flexed, semi-reclined, and reclined postures. We utilize geometric morphometric techniques, which are advantageous for evaluating shape variation and have not been extensively applied to biomechanical analyses. We found skeletal morphology to be significantly related to sex and height in all but the neutral posture (P < 0.05), and weight was marginally significantly related to shape in the semi-reclined posture (P = 0.047). Morphologically, male participants exhibited more flexion at the articulatio atlantooccipitalis than females, and females showed greater mandibular protrusion than males, although this result is likely related to height. No relationship was found between posture and TMD. This research establishes a framework for future work that uses geometric morphometric analyses to evaluate how neck postures vary in relation to TMD.

Previous work on the mandibular canal, mental foramen, and mandibular foramen has focused on humans and some other non‐primate mammals (with small sample sizes), but little work has investigated the mandibular canal and inferior alveolar nerve (IAN) across primates. However, it is important to understand the relationship between the IAN and mandibular canal due to the IAN's close relationship to the teeth and mastication, and thus dietary adaptations. While it is assumed that most bony canals within the skull grow around and form to pre‐existing nervous structures, this relationship has never been validated for the IAN and mandibular canal. MicroCT scans of 273 individuals (131 females, 134 males, and 8 unknown sex) from 68 primate species and three mammalian outgroups, and diceCT scans of 66 individuals (35 females, 23 males, and 8 unknown sex) from 33 primate species and the same mammalian outgroups were used to create 3D models of the IAN and mandibular canal from which cross‐sectional areas were taken at various points on the structures. Using qualitative descriptions, phylogenetic generalized least squares analysis, and phylogenetic ANOVAs, we were able to establish three main conclusions: (1) the mandibular canal is most often not a defined canal within the mandible of primates, (2) when the canal can be identified, the IAN does not comprise most of the space within, and (3) there are significant relationships between the IAN and the corresponding canals, with most showing isometry and the mental foramen/nerve showing negative allometry.

Tablet ownership in the United States has increased rapidly in the past decade. With this increase in tablet use comes increased levels of neck flexion compared to using a desktop or laptop computer use. These neck postures have been linked to increases in neck pain. Importantly, tablet viewing postures can be achieved in multiple ways and could be determined by either the morphology of the individual or other extraneous factors. In this study, we aim to preliminarily evaluate how neck postures vary among individuals with the goal of further examining how neck morphology and postures may be related to other factors such sex and height of the subject. We utilize geometric morphometric methods to evaluate the biomechanics of the cervical spine and skull in various neck postures; this technique is excellent for evaluating shape variation and has not been extensively applied in the biomechanical literature. Lateral‐view radiographs of 22 college‐aged subjects (10 female, 12 male) were taken seated in 5 neck postures: neutral, maximum neck flexion, upright seated tablet viewing, semi‐reclined tablet viewing, and reclined tablet viewing. In addition to the radiographs, a participant survey was completed to indicate the presence or absence of discomfort and/or abnormalities of the neck and mandible (e.g., pain, clicking/popping at the TMD, stiffness). Eighty‐seven two‐dimensional landmarks were placed on the cervical spine and skull on each radiograph signifying osteological features of the face, positions of the posterior‐most occlusal molars, the mandible, and the morphology of the cervical vertebrae. Variation among positions and subjects was visualized using principal components analysis and thin‐plate spline analysis. A series of ANOVAs and regression models were performed to examine relationships between morphology and other factors such as sex, weight, height, and the presence of symptoms related to temporomandibular joint disorder (TMD). Separate one‐way ANOVAs for each neck posture indicate that every posture but neutral is achieved differently by sex, with males tending to flex more at the atlanto‐occipital joint than females, and females showing greater protrusion in the neck than males. We further observed a significant relationship between neck flexion and height, suggesting that neck length may influence how subjects adopt specific postures. Though we did not observe a significant relationship between neck morphology or postures and the presence of TMD, these findings may provide some insight into why females experience higher rates of TMD, given that increased neck protrusion has been linked increased stresses on the temporomandibular joint and jaw. This study establishes a framework for future research that focuses on evaluating how neck postures vary in relation to TMD.Support or Funding Information Arkansas Student Undergraduate Research Fellowship University of Arkansas Provost's Collaborative Research Grant This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.