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The constrained lever model of jaw biomechanics. A ‘triangle of support’ is formed by the bite point (BITE) and the working-side (WS) and balancing-side (BS) temporomandibular joints (TMJ). During a premolar bite (a), the muscle resultant vector (MRV) of the jaw adductor (masticatory) muscles remains within the triangle (passing into the plane of the image), producing compression (green circles) at all three points as the mandible is elevated. However, during some molar bites (b), the MRV falls outside the triangle when the muscles are being recruited equally on both sides of the head, producing compression at the bite point and BS TMJ, but distraction (red circle) at the WS TMJ. To eliminate the distraction, the recruitment of the balancing-side muscles must be lessened, thereby causing the MRV to shift its position towards the working side (arrow). Once the MRV falls back within the triangle, then the WS TMJ will be in compression. A consequence of reducing the recruitment of the balancing-side muscles is that the magnitude of the bite force is reduced.
Source publication
Australopithecus sediba has been hypothesized to be a close relative of the genus Homo. Here
we show that MH1, the type specimen of A. sediba, was not optimized to produce high molar
bite force and appears to have been limited in its ability to consume foods that were
mechanically challenging to eat. Dental microwear data have previously been inter...
Contexts in source publication
Context 1
... of MH1 is well configured to consume hard foods, insofar as its facial skeleton is structurally strong (notwithstanding sampling limitations) and it appears to produce bite force efficiently. However, there is an important constraint on bite force pro- duction that argues against this interpretation. In this 'con- strained lever' model 27,28 (Fig. 4), it is assumed that the two TMJs are loaded in compression (in which the mandibular condyles are drawn into the joints). This will occur when the vector resultant of all of the masticatory muscle forces passes through a 'triangle of support' defined by the bite point and the two TMJs. If, however, the muscle resultant were to fall ...
Context 2
... during bites on the mesial teeth (that is, incisors, canines and premolars). Thus, the model 27 does not predict distraction during bites on such teeth. However, as the bite point moves distally on the tooth row towards the molars, the shape of the triangle of support changes such that a midline muscle resultant may lie outside of the triangle (Fig. 4), and thus create a distractive joint force. To bring the resultant within the triangle, one can reduce the activity levels of the balancing (non-biting) side muscles 27,28 . This has the effect of moving the muscle resultant towards the working side and back within the triangle (Fig. 4). In such bites, there is an asymmetry in the ...
Context 3
... a midline muscle resultant may lie outside of the triangle (Fig. 4), and thus create a distractive joint force. To bring the resultant within the triangle, one can reduce the activity levels of the balancing (non-biting) side muscles 27,28 . This has the effect of moving the muscle resultant towards the working side and back within the triangle (Fig. 4). In such bites, there is an asymmetry in the activity levels of the working and balancing-side muscles, a consequence of which is that overall muscle force is reduced. Thus, although one might expect that a bite on a distal tooth might produce an elevated bite force, this expectation is mitigated by the constraint that muscle force may ...
Citations
... With advances in computer software and imaging technology, FEA has reached a level of sophistication and accessibility that makes it a powerful tool in the testing of biomechanical hypotheses in studies of vertebrate form and function (Wroe et al., 2010). Increasingly, it has been applied to the study of feeding mechanics and dietary adaptations in humans and their relatives (Wroe et al., 2010(Wroe et al., , 2018Strait et al., 2013;Ledogar et al., 2016). ...
... For the FEA results we use color maps, which display areas of compressive and tensile stress of the 3D digital models. Traditionally, the color scheme used for FEA results of paleontological and biological specimens has been the classic 'rainbow' color map showing lower values in blue, higher values in red, and middle values in green and yellow (Wroe et al., 2010(Wroe et al., , 2018Ledogar et al., 2016). However, despite their ubiquitous use, numerous studies have shown that 'rainbow' color maps can be problematic due to uneven color representation and its inaccessibility for those with color vision deficiencies (Crameri et al., 2020;Lautenschlager, 2021). ...
Neanderthal anterior teeth are very large and have a distinctive morphology characterized by robust 'shovel-shaped' crowns. These features are frequently seen as adaptive responses in dissipating heavy mechanical loads resulting from masticatory and non-masticatory activities. Although the long-standing debate surrounding this hypothesis has played a central role in paleoanthropology, is still unclear if Neanderthal anterior teeth can resist high mechanical loads or not. A novel way to answer this question is to use a multidisciplinary approach that considers together tooth architecture, dental wear and jaw movements. The aim of this study is to functionally reposition the teeth of Le Moustier 1 (a Neanderthal adolescent) and Qafzeh 9 (an early Homo sapiens adolescent) derived from wear facet mapping, occlusal fingerprint analysis and physical dental restoration methods. The restored dental arches are then used to perform finite element analysis on the left central maxillary incisor during edge-to-edge occlusion. The results show stress distribution differences between Le Moustier 1 and Qafzeh 9, with the former displaying higher tensile stress in enamel around the lingual fossa but lower concentration of stress in the lingual aspect of the root surface. These results seem to suggest that the presence of labial convexity, lingual tubercle and of a large root surface in Le Moustier 1 incisor helps in dissipating mechanical stress. The absence of these dental features in Qafzeh 9 is compensated by the presence of a thicker enamel, which helps in reducing the stress in the tooth crown.
... The understanding of C2Rm represents also an anthropological challenge insofar as retrognathism is at the heart of the evolution of the hominin (Spoor et al, 1999, Puech et al., 1996, Cardini & Polly, 2013, Ledogar et al., 2016. Retrognathism or retrognathia is defined as a condition used to describe a mandible that is posterior to and behind where it should be when viewed from a lateral vantage. ...
Recent advances in the interpretability of convolutional neural networks (CNNs) have allowed applications in imaging as a novel method for visual feature extraction. We used this approach to investigate the impact of changing occlusal forces on craniofacial architecture in class II retrognathism (C2Rm) pathology. Better understanding the points of impact of C2Rm on the entire skull is a major challenge in the diagnosis, treatment, and management of this dysmorphism, but also allows to be part of the debate on changes in the shape of the skull during human evolution. To address these challenges, we introduced a methodology for extracting morphological information with an interpretable CNN (MIE-ICNN) that combines: 1) a pre-processing step to train a deep CNN, 2) an interpretability step using the Score-CAM method to explain the areas of the radiographs used by the model to identify the pathological class, and 3) a calculation step to generate a global activation map, which represents an average activation map of all classifications. The main conclusions of this study are as follows: I) the proposed technique made it possible to find the anatomical areas affected by C2Rm and already identified in the literature (i.e. the cranial base and the vertebrae), to confirm the involvement of a controversial area (the frontal sinus), and to identify a new structure (the parietal bone) as a biomarker. In addition, the study of the involvement of anatomical zones according to the severity of the dysmorphism (by the same methodology), has made it possible to propose hypotheses on the evolution of the forms of the skulls during human evolution (highlighting, in particular, the role of mastication). This new information enriches the anthropological debate around C2Rm and human evolution, and medical knowledge on the etiology of C2Rm. Finally, through this application on craniospinal architecture, the proposed methodological pipeline appears as a new toolbox to extract and visualize complex morphological systems and will certainly allow new advances in the fields of health and medical imaging.
... The most abundant C 4 plants on African savannas are the ubiquitous and diverse C 4 grasses, though wetlands can often be dominated by C 4 sedges, such as Cyperus. Early hypotheses about the tough C 4 foods that P. boisei might have been consuming rightfully considered both (e.g., Cerling et al., 2011;Lee-Thorp, 2011), and a common conclusion soon emerged that while both potentially provided food resources, grasses were unlikely to have been consumed regularly because they were deemed to be too low in protein, too high in dietary fiber, and too tough for hominin consumers without the specialized dentition and complex digestive systems of ruminant grazers (but see Sponheimer and Lee-Thorp, 2003). Thus, the storage organs of sedges were pegged as the C 4 food of choice for early hominins (e.g., Dominy et al., 2008;Dominy, 2012;Lee-Thorp et al., 2012;Yeakel et al., 2014) and it is worth noting that modern humans cultivate Cyperus esculentus for its edible tubers ('tiger nuts'). ...
... As noted earlier, paleoecological models based on modern ecological systems derive their validity by demonstrating that the focal environments/species share important parameters with what is revealed in the fossil record, and ultimately, they are deemed successful if they lead to a coherent argument for broad applicability. Morphological models are often more 'granular' in that the important issues may not be foraging strategies or landscape use but something along the lines of temporomandibular joint loading (Ledogar et al., 2016), the details of jaw movement while chewing (Rak and Hylander 2008), or risk of tooth crown fracture (Lawn et al., 2013). These are performance criteria that are typically compared between analogical pairs (e.g., Jolly [1970]: Pan is to basal hominins as Papio is to Theropithecus). ...
Despite substantial additions to the paleontological record and unanticipated improvements in analytical techniques since the Journal of Human Evolution was first published, consensus on the diet of early hominin species remains elusive. For instance, the notable advances in the analyses of hominin dental microwear and stable isotopes have provided a plethora of data that have in some instances clouded what was once ostensibly a clear picture of dietary differentiation between and within hominin taxa. In the present study, we explore the reasons why the retrodiction of diet in human evolution has proven vexing over the last half century from the perspective of both ecological and functional-mechanical models. Such models continue to be indispensable for paleobiological reconstructions, but they often contain rigid or unstated assumptions about how primary paleontological data, such as fossils and their geological and taphonomic contexts, allow unambiguous insight into the evolutionary processes that produced them. In theoretical discussions of paleobiology, it has long been recognized that a mapping function of morphology to adaptation is not one-to-one, in the sense that a particular trait cannot necessarily be attributed to a specific selective pressure and/or behavior. This article explores how the intrinsic variability within biological systems has often been underappreciated in paleoanthropological research. For instance, to claim that derived anatomical traits represent adaptations related to stereotypical behaviors largely ignores the importance of biological roles (i.e., how anatomical traits function in the environment), a concept that depends on behavioral flexibility for its potency. Similarly, in the paleoecological context, the underrepresentation of variability within the ‘edible landscapes’ our hominin ancestors occupied has inhibited an adequate appreciation of early hominin dietary flexibility. Incorporating the reality of variation at organismal and ecological scales makes the practice of paleobiological reconstruction more challenging, but in return, allows for a better appreciation of the evolutionary possibilities that were open to early hominins.
... Overlaying cofeeding events with food availability data could be useful in modeling potential areas of disease spillover events. Given that so many of the chimpanzee-gorilla interactions were observed in a feeding context, it is possible that detailed analyses of the diets and feeding adaptations in contemporaneous populations of fossil hominins (Henry et al., 2012;Ledogar et al., 2016;Martin et al., 2021) may also reveal previously unimagined insights into the paleobiology of our early relatives and ancestors. ...
Gorillas reside in sympatry with chimpanzees over the majority of their range. Compiling all known reports of overlap between apes and augmenting these with observations made over twenty years in the Ndoki Forest, we examine the potential predation-related, foraging, and social contexts of interspecific associations between gorillas and chimpanzees. We reveal a greater diversity of interactions than previously recognized, which range from play to lethal aggression. Further, there are indications that interactions between ape species may serve multiple functions. Interactions between gorillas and chimpanzees were most common during foraging activities, but they also overlapped in several other contexts. From a social perspective, we provide evidence of consistent relationships between particular chimpanzee-gorilla dyads. In addition to providing new insights into extant primate community dynamics, the diversity of interactions between apes point to an entirely new field of study in early human origins as early hominins also likely had opportunities to associate.
... Here, we show that biomechanical analysis of the A. afarensis cranium requires a re-interpretation of why australopith facial features evolved. A finite element model (FEM) of fossil specimen A.L. 444-2 [12] (an adult male A. afarensis) was constructed (electronic supplementary material) and compared to already existing models of specimens Sts 5 (an adult female A. africanus [18]), MH1 (a subadult male A. sediba [21]) and OH 5 (an adult male Paranthropus boisei [20]). The former three specimens are gracile australopiths, while the last specimen is a robust australopith. ...
... Details regarding the construction and analysis of FEMs of OH 5, Sts 5, MH1 and the chimpanzees are provided elsewhere [19][20][21], royalsocietypublishing.org/journal/rspb Proc. R. Soc. ...
... N; medial pterygoid = 263.57 N. The forces applied to the other models are reported elsewhere [19][20][21]. These forces are coarse approximations of the forces that were produced in this specimen, and indeed all of the muscle forces applied to all of the fossil hominin models are first-order approximations at best. ...
Australopiths, a group of hominins from the Plio-Pleistocene of Africa, are characterized by derived traits in their crania hypothesized to strengthen the facial skeleton against feeding loads and increase the efficiency of bite force production. The crania of robust australopiths are further thought to be stronger and more efficient than those of gracile australopiths. Results of prior mechanical analyses have been broadly consistent with this hypothesis, but here we show that the predictions of the hypothesis with respect to mechanical strength are not met: some gracile australopith crania are as strong as that of a robust australopith, and the strength of gracile australopith crania overlaps substantially with that of chimpanzee crania. We hypothesize that the evolution of cranial traits that increased the efficiency of bite force production in australopiths may have simultaneously weakened the face, leading to the compensatory evolution of additional traits that reinforced the facial skeleton. The evolution of facial form in early hominins can therefore be thought of as an interplay between the need to increase the efficiency of bite force production and the need to maintain the structural integrity of the face.
... Ma), when resource availability would have been highest, resulting in these hominins co-evolving in competition with each other (Maslin et al., 2015). Additionally, Au. sediba, P. robustus, and H. erectus were contemporaneous in South Africa between 2.04 and 1.95 Ma (Berger et al., 2008;Herries et al., 2020), coinciding with substantial changes in South African ecosystems that may have placed selective pressures on Australopithecus, leading to divergent Homo and Paranthropus lineages (Ledogar et al., 2016;Joannes-Boyau et al., 2019). ...
Climate variability and hominin evolution are inextricably linked. Yet, hypotheses examining the impact of large-scale climate shifts on hominin landscape ecology are often constrained by proxy data coming from off-site lake and ocean cores and temporal offsets between paleoenvironmental and archaeological records. Additionally, landscape response data (most commonly, records of vegetation change), are often used as a climate proxy. This is problematic as it assumes that vegetation change signifies global or regional climate shifts without accounting for the known non-linear behavior of ecological systems and the often-significant spatial heterogeneity in habitat structure and response. The exploitation of diverse, rapidly changing habitats by Homo by at least two million years ago highlights that the ability to adapt to landscapes in flux had emerged by the time of our genus’ African origin. To understand ecosystem response to climate variability, and hominin adaptations to environmental complexity and ecological diversity, we need cross-disciplinary datasets in direct association with stratified archaeological and fossil assemblages at a variety of temporal and spatial scales. In this article, we propose a microhabitat variability framework for understanding Homo’s adaptability to fluctuating climates, environments, and resource bases. We argue that the exploitation of microhabitats, or unique ecologically and geographically defined areas within larger habitats and ecoregions, was a key skill that allowed Homo to adapt to multiple climates zones and ecoregions within and beyond Africa throughout the Pleistocene.
... We analysed facial strain magnitudes and bite force leverage for simulated P 3 and M 2 bites in LB1 and compared these data with previously constructed models of modern chimpanzees (Pan troglodytes; [19]), recent humans (H. sapiens; [17]) and australopiths, including Australopithecus africanus (Sts 5; [20]), Australopithecus sediba (MH1; [21]) and Paranthropus boisei (OH5; [20]). ...
... A thermal diffusion technique [39] was used to distribute spatially heterogeneous elastic moduli throughout the cortical volume (electronic supplementary material, figure S4). Volumes of trabecular bone and those for the tooth crowns were assigned homogeneous isotropic Young's moduli of 0.637 GPa and 80 GPa, respectively, each with a Poisson's ratio of 0.318, following previous work [17,[19][20][21]. ...
... We also compared data on von Mises strain magnitude from 14 functionally homologous royalsocietypublishing.org/journal/rsfs Interface Focus 11: 20200083 locations across the facial skeleton. These locations correspond to those included in our prior research on fossil hominin feeding biomechanics [17,[19][20][21]. ...
Homo floresiensis is a small-bodied hominin from Flores, Indonesia, that exhibits plesiomorphic dentognathic features, including large premolars and a robust mandible, aspects of which have been considered australopith-like. However, relative to australopith species, H. floresiensis exhibits reduced molar size and a cranium with diminutive midfacial dimensions similar to those of later Homo , suggesting a reduction in the frequency of forceful biting behaviours. Our study uses finite-element analysis to examine the feeding biomechanics of the H. floresiensis cranium. We simulate premolar (P³ ) and molar (M² ) biting in a finite-element model (FEM) of the H. floresiensis holotype cranium (LB1) and compare the mechanical results with FEMs of chimpanzees, modern humans and a sample of australopiths (MH1, Sts 5, OH5). With few exceptions, strain magnitudes in LB1 resemble elevated levels observed in modern Homo . Our analysis of LB1 suggests that H. floresiensis could produce bite forces with high mechanical efficiency, but was subject to tensile jaw joint reaction forces during molar biting, which perhaps constrained maximum postcanine bite force production. The inferred feeding biomechanics of H. floresiensis closely resemble modern humans, suggesting that this pattern may have been present in the last common ancestor of Homo sapiens and H. floresiensis .
... Advances in three-dimensional scanning techniques, computer science and statistical shape modelling (e.g. geometric morphometrics [55], dental topography [56]) have made it possible to not only (re)construct three-dimensional digital representations of such models [9,[57][58][59][60][61], but also quantify complex shapes for statistical analyses [55,[62][63][64]. Constraints come from muscles, joints and/or the external environment. ...
... Two additional common engineering methods-FE analysis and tension/compression tests-have been used extensively in palaeoanthropology to quantify the biomechanical performance of hard skeletal tissues and address questions concerning the evolution of primate diets [12,46,58,[112][113][114]. The ability to print three-dimensional fossils further allows for the mechanical testing of previously inaccessible material [115][116][117]. ...
... Fortunately for anthroengineering, several well-respected journals have been receptive to the publication of anthroengineering manuscripts (e.g. those published by the Royal Society [106,107,134], Proceedings of the National Academy of Sciences of the United States of America [12] and Nature [58]), but more explicit definition of the field will extend this acceptance. ...
In recent decades, funding agencies, institutes and professional bodies have recognized the profound benefits of transdisciplinarity in tackling targeted research questions. However, once questions are answered, the previously abundant support often dissolves. As such, the long-term benefits of these transdisciplinary approaches are never fully achieved. Over the last several decades, the integration of anthropology and engineering through inter- and multidisciplinary work has led to advances in fields such as design, human evolution and medical technologies. The lack of formal recognition, however, of this transdisciplinary approach as a unique entity rather than a useful tool or a subfield makes it difficult for researchers to establish laboratories, secure permanent jobs, fund long-term research programmes and train students in this approach. To facilitate the growth and development and witness the long-term benefits of this approach, we propose the integration of anthropology and engineering be recognized as a new, independent field known as anthroengineering . We present a working definition for anthroengineering and examples of how anthroengineering has been used. We discuss the necessity of recognizing anthroengineering as a unique field and explore potential novel applications. Finally, we discuss the future of anthroengineering, highlighting avenues for moving the field forward.
... Most work relating diet and feeding behaviour to mandibular morphology in primates has used beam models, the limitations of which are widely acknowledged [42,[44][45][46][47], but our understanding of jaw function can be broadened using an engineering approach-finite element analysis (FEA)-which combines experimental levels of control with three-dimensional (3D) anatomical detail [42,43,[48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. Here, we present a finite element model (FEM) of the mandible of a Pan troglodytes female and compare its loading, deformation and strain regimes with those of an FEM of a mandible of a Macaca mulatta female [42,43]. ...
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 .
... Changes in functional morphology have underpinned some of the most significant evolutionary transitions in the history of life. Colonization of the land by the earliest tetrapods [1], mammalian origins and diversification [2][3][4][5], the evolution of locomotion in dinosaurs and birds [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], and functional and ecological shifts in human ancestors [24][25][26][27][28][29][30][31] represent extensively studied examples. The last two decades has seen widespread adoption of sophisticated mathematical-computational approaches to study functional morphology in extinct animals and the biomechanics of evolutionary transitions documented in the fossil record. ...
... [12,13,[19][20][21]34]), scaling values from analogous extant animals (e.g. [12,13,[24][25][26][28][29][30][31]), extrapolating values from estimated muscle attachment areas [e.g. 10,27,36,37], and computer-aided design approaches to reconstruct the size of soft tissues directly in the fossil themselves (e.g. ...
Biomechanical modelling is a powerful tool for quantifying the evolution of functional performance in extinct animals to understand key anatomical innovations and selective pressures driving major evolutionary radiations. However, the fossil record is composed predominantly of hard parts, forcing palaeontologists to reconstruct soft tissue properties in such models. Rarely are these reconstruction approaches validated on extant animals, despite soft tissue properties being highly determinant of functional performance. The extent to which soft tissue reconstructions and biomechanical models accurately predict quantitative or even qualitative patterns in macroevolutionary studies is therefore unknown. Here, we modelled the masticatory system in extant rodents to objectively test the ability of current muscle reconstruction methods to correctly identify quantitative and qualitative differences between macroevolutionary morphotypes. Baseline models generated using measured soft tissue properties yielded differences in muscle proportions, bite force, and bone stress expected between extant sciuromorph, myomorph, and hystricomorph rodents. However, predictions from models generated using reconstruction methods typically used in fossil studies varied widely from high levels of quantitative accuracy to a failure to correctly capture even relative differences between macroevolutionary morphotypes. Our novel experiment emphasizes that correctly reconstructing even qualitative differences between taxa in a macroevolutionary radiation is challenging using current methods. Future studies of fossil taxa should incorporate systematic assessments of reconstruction error into their hypothesis testing and, moreover, seek to expand primary datasets on muscle properties in extant taxa to better inform soft tissue reconstructions in macroevolutionary studies.
