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Modern humans have smaller faces relative to Middle and Late Pleistocene members of the genus Homo. While facial reduction and differences in shape have been shown to increase biting efficiency in Homo sapiens relative to these hominins, facial size reduction has also been said to decrease our ability to resist masticatory loads. This study compares crania of Homo heidelbergensis and H. sapiens with respect to mechanical advantages of masticatory muscles, force production efficiency, strains experienced by the cranium and modes of deformation during simulated biting. Analyses utilize X-ray computed tomography (CT) scan-based 3D models of a recent modern human and two H. heidelbergensis. While having muscles of similar cross-sectional area to H. heidelbergensis, our results confirm that the modern human masticatory system is more efficient at converting muscle forces into bite forces. Thus, it can produce higher bite forces than Broken Hill for equal muscle input forces. This difference is the result of alterations in relative in and out-lever arm lengths associated with well-known differences in midfacial prognathism. Apparently at odds with this increased efficiency is the finding that the modern human cranium deforms more, resulting in greater strain magnitudes than Broken Hill when biting at the equivalent tooth. Hence, the facial reduction that characterizes modern humans may not have evolved as a result of selection for force production efficiency. These findings provide further evidence for a degree of uncoupling between form and function in the masticatory system of modern humans. This may reflect the impact of food preparation technologies. These data also support previous suggestions that differences in bite force production efficiency can be considered a spandrel, primarily driven by the midfacial reduction in H. sapiens that occurred for other reasons. Midfacial reduction plausibly resulted in a number of other significant changes in morphology, such as the development of a chin, which has itself been the subject of debate as to whether or not it represents a mechanical adaptation or a spandrel.

Alveolar bone, together with the underlying trabecular bone, fulfils an important role in providing structural support against masticatory forces. Diseases such as osteoporosis or periodontitis cause alveolar bone resorption which weakens this structural support and is a major cause of tooth loss. However, the functional relationship between alveolar bone remodelling within the molar region and masticatory forces is not well understood. This study investigated this relationship by comparing mammalian species with different diets and functional loading (Felis catus, Cercocebus atys, Homo sapiens, Sus scrofa, Oryctolagus cuniculus, Ovis aries). We performed histomorphometric analyses of trabecular bone morphology (bone volume fraction, trabecular thickness and trabecular spacing) and quantified the variation of bone and tooth root volumes along the tooth row. A principal component analysis and non-parametric MANOVA showed statistically significant differences in trabecular bone morphology between species with contrasting functional loading, but these differences were not seen in sub-adult specimens. Our results support a strong, but complex link between masticatory function and trabecular bone morphology. Further understanding of a potential functional relationship could aid the diagnosis and treatment of mandibular diseases causing alveolar bone resorption, and guide the design and evaluation of dental implants.

Finite element analysis (FEA) is increasingly applied in skeletal biomechanical research in general, and in fossil studies in particular. Underlying such studies is the principle that FEA provides results that approximate reality. This paper provides further understanding of the reliability of FEA by presenting a validation study in which the deformations experienced by a real cadaveric human cranium are compared to those of an FE model of that cranium under equivalent simulated loading. Furthermore, model sensitivity to simplifications in segmentation and material properties is also assessed. Our results show that absolute deformations are not accurately predicted, but the distribution of the regions of relatively high and low strains, and so the modes of global deformation, are reasonably approximated.

Island subspecies of the Arctic fox Vulpes lagopus differ morphologically from the mainland subspecies. In particular, differences in cranial form may reflect varied biomechanical adaptations associated with hunting and feeding behaviours. We tested the hypothesis that the observed cranial differences between two island foxes (living on two North Pacific islands) and those living on the mainland have no impact on biomechanical performance during simulated biting. 3D cranial models of three Arctic fox subspecies were compared based on biomechanical parameters (e.g. local strain and large-scale deformation). Finite elements (FE) analyses were used to simulate equivalent biting loads, and geometric morphometrics was used to compare the modes of deformation among the models. The results showed differences in local strains and modes of global deformation among the three subspecies; the mainland subspecies was particularly distinct from the island subspecies. The representative cranium of the mainland subspecies experienced higher strain than that of both island subspecies during all bites. However, the findings highlight issues that arise when relating biomechanical performance, measured via FE analyses, to the foods consumed rather than to the mechanical properties of the individual’s diet. Additional physical properties data for each prey type are necessary to determine the extent to which the present findings reflect biomechanical adaptations to diet and prey acquisition.

The study of morphological variation in the hominin fossil record has been transformed in recent years by the advent of high resolution 3D imaging combined with improved geometric morphometric (GM) toolkits. In parallel, increasing numbers of studies have applied finite elements analysis (FEA) to the study of skeletal mechanics in fossil and extant hominoid material. While FEA studies of fossils are becoming ever more popular they are constrained by the difficulties of reconstruction and by the uncertainty that inevitably attaches to the estimation of forces and material properties. Adding to these modelling difficulties it is still unclear how FEA analyses should best deal with species variation. Comparative studies of skeletal form and function can be further advanced by applying tools from the GM toolkit to the inputs and outputs of FEA studies. First they facilitate virtual reconstruction of damaged material and can be used to rapidly create 3D models of skeletal structures. Second, GM methods allow variation to be accounted for in FEA by warping models to represent mean and extreme forms of interest. Third, GM methods can be applied to compare FEA outputs the ways in which skeletal elements deform when loaded. Model comparisons are hampered by differences in material properties, forces and size among models but how deformations from FEA are impacted by these parameters is increasingly well understood, allowing them to be taken into account in comparing FEA outputs. In this paper we review recent advances in the application of GM in relation to FEA studies of craniofacial form in hominins, providing examples from our recent work and a critical appraisal of the state of the art. info:eu-repo/semantics/publishedVersion

In recent years finite element analysis (FEA) has emerged as a useful tool for the analysis of skeletal form-function relationships. While this approach has obvious appeal for the study of fossil specimens, such material is often fragmentary with disrupted internal architecture and can contain matrix that leads to errors in accurate segmentation. Here we examine the effects of varying the detail of segmentation and material properties of teeth on the performance of a finite element model of a Macaca fascicularis cranium within a comparative functional framework. Cranial deformations were compared using strain maps to assess differences in strain contours and Procrustes size and shape analyses, from geometric morphometrics, were employed to compare large scale deformations. We show that a macaque model subjected to biting can be made solid, and teeth altered in material properties, with minimal impact on large scale modes of deformation. The models clustered tightly by bite point rather than by modeling simplification approach, and fell out as being distinct from another species. However localized fluctuations in predicted strain magnitudes were recorded with different modeling approaches, particularly over the alveolar region. This study indicates that, while any model simplification should be undertaken with care and attention to its effects, future applications of FEA to fossils with unknown internal architecture may produce reliable results with regard to general modes of deformation, even when detail of internal bone architecture cannot be reliably modeled.

Objectives Changes to soft- and hard-tissue components of the masticatory complex during development can impact functional performance by altering muscle excursion potential, maximum muscle forces, and the efficiency of force transfer to specific bitepoints. Within Macaca fascicularis, older individuals exploit larger, more mechanically resistant food items and more frequently utilize wide-gape jaw postures. We therefore predict that key architectural and biomechanical variables will scale during ontogeny to maximize bite force and gape potential within older, larger-bodied individuals. Materials and methods We analyzed 26 specimens of M. fascicularis, representing a full developmental spectrum. The temporalis, superficial masseter, and deep masseter were dissected to determine muscle mass, fiber length, and physiologic cross-sectional area (PCSA). Lever-arm lengths were also measured for each muscle, alongside the height of the temporomandibular joint (TMJ) and basicranial length. These variables were scaled against two biomechanical variables (jaw length and condyle-molar length) to determine relative developmental changes within these parameters. Results During ontogeny, muscle mass, fiber length, and PCSA scaled with positive allometry relative to jaw length and condyle-molar length within all muscles. TMJ height also scaled with positive allometry, while muscle lever arms scaled with isometry relative to jaw length and with positive allometry (temporalis) or isometry (superficial and deep masseter) relative to condyle-molar length. Conclusion Larger individuals demonstrate adaptations during development towards maximizing gape potential and bite force potential at both an anterior and posterior bitepoint. These data provide anatomical evidence to support field observations of dietary and behavioral differences between juvenile and adult M. fascicularis.

Dielectric measurements provide valuable information about the properties of materials, and could be used to classify and identify the source of objects, in fields such as archaeology. Current methods of identification are all partly destructive, so an innovative electromagnetic method developed by the authors, based on resonant cavity perturbation (RCP), provides an attractive, non-destructive alternative. A problem with traditional RCP is that the changes in frequency and Q-factor vary with the object’s shape; however we overcome this by creating a replica of the object, from a material whose dielectric properties are known. Then, by combining three separate perturbations with orthogonal field directions, due firstly to the object and then to its replica, we eliminate the shape dependency, and thus determine the object’s dielectric constant and loss factor. After developing the theory of this novel DRM technique, we demonstrate the principle using a set of geometric shapes made in both polytetrafluoroethylene (PTFE) and a 3D printed material. Further measurements then enable second-order terms to be included in the model, improving its accuracy. Finally, DRM is shown to be capable of distinguishing two irregularly shaped objects of different materials. Potential applications of DRM include determining the provenance of pottery, glasses and flints, and distinguishing ivory from bone. These would be of interest to customs and environmental agencies, as well as museum curators and archaeologists.

In 2015 an engraved shale pendant was found during excavations at the Early Mesolithic site of Star Carr, UK. Engraved motifs on Mesolithic pendants are extremely rare, with the exception of amber pendants from southern Scandinavia. The artwork on the pendant is the earliest known Mesolithic art in Britain; the 'barbed line' motif is comparable to styles on the Continent, particularly in Denmark. When it was first uncovered the lines were barely visible but using a range of digital imaging techniques it has been possible to examine them in detail and determine the style of engraving as well as the order in which the lines might have been made. In addition, microwear and residue analyses were applied to examine whether the pendant showed signs that it had been strung or worn, and whether the lines had been made more visible through the application of pigments, as has been suggested for some Danish amber pendants. This approach of using multiple scientific and analytical techniques has not been used previously and provides a methodology for the examination of similar artefacts in the future.

Shamanic belief systems represent the first form of religious practice visible within the global archaeological record. Here we report on the earliest known evidence of shamanic costume: modified red deer crania headdresses from the Early Holocene site of Star Carr (c. 11 kya). More than 90% of the examples from prehistoric Europe come from this one site, establishing it as a place of outstanding shamanistic/cosmological significance. Our work, involving a programme of experimental replication, analysis of macroscopic traces, organic residue analysis and 3D image acquisition, metrology and visualisation, represents the first attempt to understand the manufacturing processes used to create these artefacts. The results produced were unexpected-rather than being carefully crafted objects, elements of their production can only be described as expedient.

Finite element analysis (FEA) is a modelling technique increasingly used in anatomical studies investigating skeletal form and function. In the case of the cranium this approach has been applied to both living and fossil taxa to (for example) investigate how form relates to function or infer diet or behaviour. However, FE models of complex musculoskeletal structures always rely on simplified representations because it is impossible completely to image and represent every detail of skeletal morphology, variations in material properties and the complexities of loading at all spatial and temporal scales. The effects of necessary simplifications merit investigation. To this end, this study focuses on one aspect, model geometry, which is particularly pertinent to fossil material where taphonomic processes often destroy the finer details of anatomy or in models built from clinical CTs where the resolution is limited and anatomical details are lost. We manipulated the details of a finite element (FE) model of an adult human male cranium and examined the impact on model performance. First, using digital speckle interferometry, we directly measured strains from the infraorbital region and frontal process of the maxilla of the physical cranium under simplified loading conditions, simulating incisor biting. These measured strains were then compared with predicted values from FE models with simplified geometries that included modifications to model resolution, and how cancellous bone and the thin bones of the circum-nasal and maxillary regions were represented. Distributions of regions of relatively high and low principal strains and principal strain vector magnitudes and directions, predicted by the most detailed FE model, are generally similar to those achieved in vitro. Representing cancellous bone as solid cortical bone lowers strain magnitudes substantially but the mode of deformation of the FE model is relatively constant. In contrast, omitting thin plates of bone in the circum-nasal region affects both mode and magnitude of deformation. Our findings provide a useful frame of reference with regard to the effects of simplifications on the performance of FE models of the cranium and call for caution in the interpretation and comparison of FEA results.

During development the masticatory apparatus undergoes significant changes; including changes in muscle size and orientation, and in dental form due to replacement and wear. As body size increases during development, absolute masticatory forces are predicted to increase. However the effect of simultaneous changes to muscle lever mechanics and dental topography upon masticatory performance is currently unknown. Cercocebus atys (the sooty mangabey) provides an ideal opportunity to examine this. Over 50% of the diet among all post-weaning individuals centres upon exploiting a mechanically stress resistant seed. Given this dietary consistency, it may be expected that the masticatory system will be integrated across development; such that individuals of all ages are capable of processing this food item. Using virtual modelling techniques, changes in bite pressure along the postcanine dental row were predicted at various stages of development. Results indicate that while maximum muscle force production increase...