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Visual overview of the muscle attachment (regions and directional vector) in 3D and 2D models. A.) Oblique view of 3D complete model showing regions of superficial masseter, deep masseter, anterior temporalis, posterior temporalis and medial pterygoid attachments on buccal and lingual sides of the mandible (face loadings). Vectors (at centroid of mandibular attachment area) are directed towards the centroid of 3D cranial attachment areas B.) Lateral view of 2D planar model showing regions of nodal forces applied to model. Outlined regions correspond to attachment areas of the superficial masseter, deep masseter, anterior temporalis, posterior temporalis and medial pterygoid on the mandibular surface (XY plane). Z-components of muscle force have been removed and vectors (tail at centroid of mandibular attachment area) are directed towards the centroid of 2D cranial attachment areas (in XY plane). Please note: Muscles have been mapped in lateral view, but forces applied to 2D planar model are nodal, not face loads.

Definitions of terms used to describe loading, deformation and strain regimes following Ross et al., 2011, Panagiotopoulou et al., 2020 and Smith et al., 2021.

Supplementary methods and data

Models are mathematical representations of systems, processes, or phenomena. In biomechanics, finite-element modelling (FEM) can be a powerful tool, allowing biologists to test form-function relationships in silico, replacing or extending results of in vivo experimentation. Although modelling simplifications and assumptions are necessary, as a minimum modelling requirement the results of the simplified model must reflect the biomechanics of the modelled system. In cases where the three-dimensional mechanics of a structure are important determinants of its performance, simplified two-dimensional modelling approaches are likely to produce inaccurate results. The vertebrate mandible is one among many three-dimensional anatomical structures routinely modelled using two-dimensional FE analysis. We thus compare the stress regimes of our published three-dimensional model of the chimpanzee mandible to a published two-dimensional model of the chimpanzee mandible and identify several fundamental differences. We then present a series of two-dimensional and three-dimensional FE modelling experiments that demonstrate how three key modelling parameters; (1) dimensionality, (2) symmetric geometry, and (3) constraints affect deformation and strain regimes of the models. Our results confirm that, in the case of the primate mandible (at least), two-dimensional FEM fails to meet this minimum modelling requirement and should not be used to draw functional, ecological or evolutionary conclusions.

The mechanical behaviour of the mandibles of Pan and Macaca during mastication was compared using finite-element modelling. Muscle forces were calculated using species-specific measures of physiological cross-sectional area and scaled using electromyographic estimates of muscle recruitment in Macaca. Loading regimes were compared using moments acting on the mandible and strain regimes were qualitatively compared using maps of principal, shear and axial strains. The enlarged and more vertically oriented temporalis and superficial masseter muscles of Pan result in larger sagittal and transverse bending moments on both working- and balancing-sides, and larger anteroposterior twisting moments on the working-side. The mandible of Pan experiences higher principal strain magnitudes in the ramus and mandibular prominence, higher transverse shear strains in the top of the symphyseal region and working-side corpus, and a predominance of sagittal bending-related strains in the balancing-side mandible. This study lays the foundation for a broader comparative study of Hominidae mandibular mechanics in extant and fossil hominids using finite-element modelling. Pan's larger and more vertical masseter and temporalis may make it a more suitable model for hominid mandibular biomechanics than Macaca.

Supplemental Figures (5) & Supplemental Tables (3)

Australopiths exhibit a number of derived facial features that are thought to strengthen the face against high and/or repetitive loads associated with a diet that included mechanically challenging foods. Here, we use finite element analysis (FEA) to test hypotheses related to the purported strengthening role of the zygomatic root and “anterior pillar” in australopiths. We modified our previously constructed models of Sts 5 (Australopithecus africanus) and MH1 (A. sediba) to differ in the morphology of the zygomatic root, including changes to both the shape and positioning of the zygomatic root complex, in addition to creating variants of Sts 5 lacking anterior pillars. We found that both an expanded zygomatic root and the presence of “anterior pillars” reinforce the face against feeding loads. We also found that strain orientations are most compatible with the hypothesis that the pillar evolved to resist loads associated with premolar loading, and that this morphology has an ancillary effect of strengthening the face during all loading regimes. These results provide support for the functional hypotheses. However, we found that an anteriorly positioned zygomatic root increases strain magnitudes even in models with an inflated/reinforced root complex. These results suggest that an anteriorly placed zygomatic root complex evolved to enhance the efficiency of bite force production while facial reinforcement features, such as the anterior pillar and the expanded zygomatic root, may have been selected for in part to compensate for the weakening effect of this facial configuration. Anat Rec, 300:171–195, 2017. © 2016 Wiley Periodicals, Inc.

Every year in the U.S, college students face a range of consequences as a result of alcohol consumption. College students who consume alcohol create problems not only for themselves, but also for their peers and the higher education institutions they attend. Despite all of the attention from the research community, laws created by federal and state governments, and prevention efforts put forth by higher education institutions, the degree of alcohol consumption, binge drinking, and significance of alcohol-related problems on U.S. college and university campuses has remained a serious and unchanged problem for 30 years. Comprehensive evidence-based alcohol prevention programs offer the greatest opportunity for positive behavior modification in college students in terms of alcohol use. The purpose of this qualitative, collective case study was to identify and explore strategies within comprehensive alcohol prevention programs at the colleges and universities which incorporate them. Of specific interest was the criteria these institutions use when selecting alcohol prevention programs and the perceived barriers that are preventing institutions which are not offering comprehensive alcohol prevention programs, from incorporating them. Data collection began with email requests for participants to complete a 10 question structured survey. From those responses, eight participants were purposively selected to participate in semi-structured interviews. In addition, documents from the institutions were requested and analyzed and institution websites were reviewed to advance further understanding of the information and increase trustworthiness of the study. Data analysis was conducted using the constant-comparative method and consisted of open and axial coding. This study is significant in that it identified best practices used by colleges and universities to develop impactful comprehensive evidence-based alcohol prevention programs and revealed the criteria these institutions use when selecting or developing these prevention programs. Trustworthiness was established through credibility, confirmability, dependability and transferability, using member checking, reflexive journaling, audit trails, and by providing thick, rich description. The results of this study support the effectiveness of comprehensive evidence-based alcohol prevention programs on college and university campuses. Participants described very similar program components including required alcohol education for freshmen, required interventions for students in violation of the student code of conduct regarding alcohol use, peer educator programs, and community and campus alcohol committees and coalitions. Other results from this study included: 1) the lack of a common definition of what constitutes the success of a comprehensive evidence-based alcohol prevention program; 2) the unanimous focus on harm reduction as opposed to an abstinence only approach to alcohol prevention; 3) various identified methods of selecting individual components that fall within the comprehensive program; and 4) perceived barriers preventing higher education institutions from implementing comprehensive evidence-based alcohol prevention programs such as the taboo nature of alcohol prevention on college campuses, an unfair perception that alcohol is a campus problem as opposed to a societal issue, and inadequate staff needed to implement comprehensive programs. The results of this study suggest implications and recommendations for higher education practice. Implications include: 1) the need for higher education institutions to implement comprehensive evidence-based alcohol prevention programs in order to effectively address alcohol use by students; 2) the importance of abandoning abstinence based prevention efforts to focus on the underlying issue which is reducing harm that occurs as a result of alcohol consumption; 3) the need to establish baseline data specific to the campus and develop campus specific definitions of success to determine best practices for the campus and also to avoid damaging comparisons to other colleges and universities who operate under different demographics; and 4) the necessity of administrator support in alcohol prevention initiatives to advance campus efforts. Recommendations for the practice of higher education include: 1) the need for colleges and universities to hire qualified staff to lead alcohol prevention efforts; 2) recruitment of administrative support for alcohol prevention programs; 3) community involvement in campus alcohol prevention efforts; and 4) the incorporation of evidence-based program components within the comprehensive alcohol prevention program.