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This study characterizes the structure and heterogeneous anisotropic elastic properties of mandibular bone in an adult female specimen of Macaca fascicularis. We determine properties in alveolar, midcorpus, and basal regions of buccolingual cross sections taken from multiple corpus and ramus locations. Within sections, we determine properties from endosteal, midcortical, and periosteal regions. The combined experimental techniques of reflected light microscopy and Knoop microindentation are used within the context of elasticity tensor transformation equations. Reflected microscopy enables the visualization of local principal material directions. Bone is sampled with a Knoop indenter, a diamond rhombohedral pyramid that creates an indentation with major and minor axes. Elastic constants are determined by varying the orientation of the indenter with respect to the material directions and applying the transformation equations. We find regional variations in bone structure, including bands of orthotropic circumferential lamellar bone at the endosteal and periosteal corpus base, angular region, and ramus. Transversely isotropic osteonal bone characterizes the midcortices of alveolar and basal regions, with many resorption spaces in alveolar regions. Regional variations in elasticity include stiffer bone with greater orthotropy in the endosteal molar regions compared to the periosteal angle region. Stiffness increases posteriorly within the midcortical molar region, and is less in alveolar compared to basal regions. Considerable variation exists in structure and material properties on a highly localized scale, and such data provide for more realistic modeling of stress in structural models.

Comparative study of primate jaw morphology has long sought to relate the mechanical demands of diet to size and shape of the mandible. In sympatric colobines, predicted differences in mandibular morphology attributable to diet ate not observed; structurally weaker symphyses are associated with more obdurate diets (Int. J. Primatol. 22:1033-1055), a finding which undermines the premise of a functional linkage between diet and morphology. One explanation for these results is that linear measures used to infer biomechanical performance poorly estimate bone behavior. We explore this possibility by comparing predicted levels of strain with those observed experimentally in 6 mandibles representing Colobus polykomos and Procolobus badius under lateral transverse bending loads, the major source of masticatory stress in anthropoid symphyses. We treat the mandible as a curved elliptical beam and also directly section specimens to calculate area properties. Our results depict differences in labial and lingual strains that are below the disparities predicted by mathematical formulae for curved beams, and labial strain gradients vary in both steepness and direction. These observations indicate that substantial errors are associated with morphometric models, but these errors may only partially account for the poor fit between jaw form and diet among closely related species. Supported by NSF BCS-0096037.

Objectives: We evaluated the effects of four treatments for pathogen inactivation in bone tissue (ethanol storage, formalin fixation, gamma irradiation, and heat treatment via autoclave) on stiffness and anisotropy values in bone samples., Materials and Methods: Cortical bone samples from the humerus of 14 bovine specimens were subjected to Knoop microindentation analysis in longitudinal and transverse planes of section and four indenter orientations within each section. From each specimen, individual samples were assigned to one of five treatment conditions: 50% ethanol-saline solution, formalin immersion, gamma irradiation, autoclave, and buffered saline (controls). Each sample was microindented 100 times and the resultant stiffness data were analyzed by a resampled factorial analysis of variance., Results: First- and second-order interactions as well as main effects of indenter orientation, treatment, and specimen were significant for both transverse and longitudinal sections, with the sole exception that indenter orientation-treatment interaction was nonsignificant for longitudinal sections. Interaction plots reveal that thermal (autoclave) and irradiation treatments depress stiffness values the most, while patterns of indentation stiffness at different orientations are relatively unaffected., Discussion: Patterns of anisotropy are relatively unaffected by preservative treatments, but elastic modulus changes are consistent and unambiguous. Formalin and ethanol treatments are most comparable to controls and represent the best preservative media for mechanical testing. These options, however, are likely to be the least effective for ensuring the inactivation or sterilization of potentially contaminated samples., (© 2024 Wiley Periodicals LLC.)

Objectives: Although a bounding gait is practiced by a diversity of animals, the morphological characteristics, kinematics, and energetics associated with this locomotor form remain poorly understood. This study focuses on the locomotor anatomy of two species of African colobine monkeys (Piliocolobus badius, a leaper, and Colobus polykomos, a leaper-bounder) in an effort to assess if bounding should be considered a unique primate locomotor category or is better viewed as a behavior on a leaping continuum., Materials and Methods: A total of 53 femora, 28 humeri, and 45 ossa coxae from the two species provide comparative morphological data. Free-body models of bounding and leaping are presented to characterize loading conditions. Species differences in morphometric traits are evaluated via parametric and nonparametric tests (i.e., analysis of variance, resampling)., Results: C. polykomos exhibits traits that align more closely with putative leaping specializations when compared to P. badius (e.g., large femoral head, long femur, low femoral neck angle), while also possessing certain traits that are not (e.g., long femoral neck and reduced relative femoral robusticity). Consequently, C. polykomos likely experiences absolutely greater joint forces at the hip and higher bending at the femoral neck both when it leaps and bounds, given equivalent accelerations in bounding and leaping., Discussion: Bounding is best described as a form of low-acceleration leaping. If bounding has lower acceleration requirements relative to leaping, C. polykomos achieves locomotor competence with less energy, relatively smaller bending moments, and reduced joint forces., (© 2023 Wiley Periodicals LLC.)

(1) Background: Bacillus cereus biovar anthracis (Bcbva) was the causative agent of an anthrax-like fatal disease among wild chimpanzees in 2001 in Côte d'Ivoire. Before this, there had not been any description of an anthrax-like disease caused by typically avirulent Bacillus cereus. Genetic analysis found that B. cereus had acquired two anthrax-like plasmids, one a pXO1-like toxin producing plasmid and the other a pXO2-like plasmid encoding capsule. Bcbva caused animal fatalities in Cameroon, Democratic Republic of Congo, and the Central African Republic between 2004 and 2012. (2) Methods: The pathogen had acquired plasmids in the wild and that was discovered as the cause of widespread animal fatalities in the early 2000s. Primate bones had been shipped out of the endemic zone for anthropological studies prior to the realized danger of contamination with Bcbva. Spores were isolated from the bone fragments and positively identified as Bcbva. Strains were characterized by classical microbiological methods and qPCR. Four new Bcbva isolates were whole-genome sequenced. Chromosomal and plasmid phylogenomic analysis was performed to provide temporal and spatial context to these new strains and previously sequenced Bcbva. Tau and principal component analyses were utilized to identify genetic and spatial case patterns in the Taï National Park anthrax zone. (3) Results: Preliminary studies positively identified Bcbva presence in several archival bone fragments. The animals in question died between 1994 and 2010. Previously, the earliest archival strains of Bcbva were identified in 1996. Though the pathogen has a homogeneous genome, spatial analyses of a subset of mappable isolates from Taï National Park revealed strains found closer together were generally more similar, with strains from chimpanzees and duikers having the widest distribution. Ancestral strains were located mostly in the west of the park and had lower spatial clustering compared to more recent isolates, indicating a local increase in genetic diversity of Bcbva in the park over space and time. Global clustering analysis indicates patterns of genetic diversity and distance are shared between the ancestral and more recently isolated type strains. (4) Conclusions: Our strains have the potential to unveil historical genomic information not available elsewhere. This information sheds light on the evolution and emergence of a dangerous anthrax-causing pathogen.

The role of mechanical stimuli in promoting endochondral ossification during somatic growth and maturation remains an active area of research. This study employs a pisiform model of endochondral ossification to investigate the potential role of mechanobiological signals in the appearance and development of ossification centers and to develop theoretical applications to the primate basicranium. We constructed finite element models based on the structure of a human pisiform within the flexor carpi ulnaris tendon. The pisiform was assigned initial material properties of hyaline cartilage, and tendon properties were based on in situ observations drawn from the literature. A macaque growth model was used to simulate increased load over time as a function of body mass. A load case of uniaxial tension from the tendon was applied over 208 iterations, to simulate weekly growth over a 4-year span. The mechanical signal was defined as shear stress. Element stresses were evaluated in each iteration, with elements exceeding the yield threshold subsequently assigned a higher elastic modulus to mimic mechanically driven mineralization. Three unique mineralization rates were tested. Regardless of rate, all ossification simulations predict a pisiform with heterogeneous stiffness through alternating periods of material stasis and active mineralization/ossification. Assuming metabolic processes underlying endochondral ossification are similar throughout the body, our model suggests that a mechanical signal alone is an insufficient stimulus in the etiology of bone formation through endochondral ossification. Consequently, given the general validity of the simulation, endochondral ossification cannot be fully explained in terms of mechanical stimuli., (© 2023 American Association for Anatomy.)

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., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Three guenon species in Taï National Park frequently form and maintain stable polyspecific associations despite significant feeding competition. This dietary overlap provides an opportunity to examine how closely related and anatomically similar taxa process the same foods. Our research examines whether the oral-processing behaviors of these guenons differ when they consume the same foods. Methods: Data on oral-processing behavior were collected on one habituated group each of Cercopithecus campbelli , C. diana, and C. petaurista in Taï National Park, Côte d'Ivoire from January 2016 to December 2018. We recorded the frequency with which foods were introduced to the mouth (ingestive action) and the frequency with which foods were processed using incisors, canines, and postcanine teeth. Oral-processing profiles for species-specific plant foods, fungi, and invertebrates were compared using Monte Carlo resampling. We quantified oral-processing behavior during a total of 2316 five-minute focal periods. Diana monkeys use their incisors significantly more per ingestive action than Campbell's monkeys or Lesser spot-nosed guenons. Lesser spot-nosed guenons use their incisors more than Campbell's monkeys. Diana monkeys also use significantly more post-canine chews per ingestive action than Campbell's monkeys and Lesser spot-nosed guenons. Lesser spot-nosed guenons generally use fewer post-canine chews than Diana monkeys but more than Campbell's monkeys. Canine use during feeding was rare in all three taxa. The three study species use different oral-processing profiles when consuming the same foods. These results are intriguing given the overall similarity in dental and cranial anatomy in these taxa. The oral-processing profiles we report do not encompass the full dietary breadth of all species; however, the behavioral diversity demonstrated during consumption of the same foods suggests that insight into feeding behavior is more likely obtained by examining oral processing of individual foods rather than broad food categories. Furthermore, these results underscore that important variation in feeding behavior is not necessarily associated with morphological differences in dental or craniofacial anatomy.

The olive colobus (Procolobus verus) is the smallest extant colobine. Based on the axiom that folivory is associated with larger body mass, the olive colobus is expected to be less folivorous than its sister taxon Piliocolobus badius, but previous studies show that the opposite is true. Here we test the hypothesis that masticatory and ingestive effort in the olive colobus is greater due to allometric factors related to bite force scaling and throughput of ingested foods. We analyzed oral processing data collected on olive colobus in the Taï Forest, Ivory Coast, between May 2016 and May 2018. We compare these with previously published data on P. badius and Colobus polykomos from Taï. In terms of overall feeding effort, olive colobus invest more effort (i.e., chewing cycles) than the larger colobines. When contrasts are restricted to commonly consumed foods, this greater energetic investment is not consistently observed. Ingestion of young leaves is associated with a reduced number of masticatory cycles in all three colobine species. A slightly elevated average effort in the olive colobus during young leaf feeding suggests this food source is more challenging in smaller monkeys, but mature leaf processing effort is generally the same among Taï colobines. Thus, for olive colobus, leaf ductility may be more problematic than leaf toughness in terms of masticatory effort. While there may be an allometric cost to being a small colobine, food selectivity is an important mitigating factor., (© 2022. The Author(s), under exclusive licence to Japan Monkey Centre.)

Differences in dentin microstructure have been used as a tool for dietary reconstruction; however, the extent that diet is associated with this aspect of dental morphology has yet to be empirically tested. We conducted microhardness tests of mammalian dentin sections, hypothesizing that species with adaptations to particularly hard diets would have softer dentin, owing to a higher proportion of soft intertubular dentin. Species adapted to abrasive diets, in contrast, should have harder dentin, resulting from a higher proportion of hypermineralized peritubular dentin. We examined molar dentin hardness in ten mammalian taxa with durophagous diets, abrasive diets, and a comparative "control" group of mechanical generalists. Samples included six primate taxa and four non-primate species representing various dietary regimes. Our results reveal significant variation among taxa in overall hardness, but the data do not distinguish between hard and abrasive diets. Several taxa with generalized (i.e., mechanically diverse) diets resemble each other in exhibiting large variance in hardness measurements and comparably soft dentin. The high variation in these species appears to be either a functional signal supporting the niche variation hypothesis or indicate the absence of sustained unidirectional selective pressure. A possible phylogenetic signal of dentin hardness in the data also holds promise for future systematic investigations., (© 2021 Wiley Periodicals LLC.)

The question of which mechanical variables are responsible for inducing osteogenic activity is unresolved despite extensive experimental and theoretical investigation. Candidate variables include strain magnitude, loading frequency, the interaction of magnitude and frequency (strain rate), and strain gradients. An additional challenge is discerning the coordination of periosteal and endosteal expansion during growth, and whether this coordination (or lack thereof) is fully dependent or partially independent of the local mechanical environment. In this study, under the assumption that calculated stresses correspond to relative strain magnitudes, we specify alternative growth algorithms of bone cross-sectional size and geometry to explore skeletal growth under alternative scenarios of osteogenic activity that are tracking 1) an attractor stress, 2) local stress magnitude or 3) steepness of stress gradients. These developmental simulations are initiated from two initial geometries (symmetrical and asymmetrical ellipses) under a time-varying torsional load whose magnitude is proportional to body size growth in a model primate. In addition, we model endosteal expansion under three conditions hypothesized in the literature, in which endosteal expansion is 1) independent of the mechanical milieu, 2) completely dependent on the mechanical milieu, and 3) a "hybrid" model in which intrinsic biological (independent) growth is operative early but gives way to mechanically-sensitive (dependent) growth at later ages. Three variables were recorded over each growth simulation: the safety factor (ratio of yield stress to actual stress), an efficiency ratio (invested bone area per unit of stress), and proximity to an isostress condition (an optimal design criterion in which stress is invariant throughout the structure). The attractor stress algorithm produces the most "adapted" bones in terms of mechanical competence and economy of material. Localized osteogenic activity that is guided in direct proportion to stress magnitude produces competent bones but with variable adult geometries depending on conditions of endosteal expansion. Stress gradients also produce functional but relatively inefficient bones, with widely variable safety factors during growth and heterogeneous stress fields. If, in fact, the osteocyte network monitors strain gradients to generate osteogenic signals, the resulting morphology is competent but falls well short of an optimal mechanical solution., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The material property of leaf toughness is considered the crucial mechanical challenge facing folivorous primates. Mature leaves have higher recorded toughness values than young leaves on average, leading to many assumptions about the patterning of food breakdown that follow a tough/not-tough dichotomy. We tested three hypotheses about how leaves break down under repetitive loading cycles, predicting that mature leaves (i) experience more force during simulated occlusal loads, (ii) more effectively resist fragmentation into small pieces, and (iii) show a more gradual decline in resistance over consecutive cycles than young leaves. Under displacement control using a mechanical testing system, we subjected young and mature leaves to 20 cycles of axial loading using interlocking steel wedges, then collected and quantified the size of the leaf fragments. While we found that mature leaves experienced more overall force than young leaves ( p < 0.001), they also shattered into smaller pieces ( p = 0.004) and showed a steeper decline in their resistance to the cycles over the course of a test ( p < 0.01). These results suggest that putatively 'tougher' foods (i.e. mature versus young leaves) do not necessarily resist fragmentation as commonly assumed. The current tough/not-tough paradigm of primate foods may not accurately reflect how leaves break down during masticatory behaviour., (© 2021 The Author(s).)

Objectives: The function of the browridge in primates is a subject of enduring debate. Early studies argued for a role in resisting masticatory stresses, but recent studies have suggested sexual signaling as a biological role. We tested associations between circumorbital form, diet, oral processing, and social behavior in two species of colobus monkey-the king colobus (Colobus polykomos) and western red or bay colobus (Piliocolobus badius)., Materials and Methods: We quantified circumorbital size and dimorphism in a sample of 98 crania. Controlling for age and facial size, we tested whether variation in circumorbital morphology can be explained by variation in diet, oral processing behavior, masticatory muscle size, and mating system. To contextualize our results, we included a broader sample of facial dimorphism for 67 anthropoid species., Results: Greater circumorbital thickness is unrelated to the stresses of food processing. King colobus engages in longer bouts of anterior tooth use, chews more per ingestive event, and processes a tougher diet, yet circumorbital thickness of C. polykomos is reduced compared to P. badius. Differences in circumorbital development do not vary with wear or facial size. Greater sexual dimorphism is present in P. badius; comparisons across anthropoids indicated patterns of circumorbital dimorphism were decoupled from overall size dimorphism., Conclusions: The expanded circumorbits of male red colobus monkeys evolved in response to intense male-male competition. This hypothesis is consistent with the pattern across anthropoid primates and highlights the underappreciated role of sexual selection in shaping the primate face., (© 2021 Wiley Periodicals LLC.)

The sooty mangabey (Cercocebus atys) practices year-round durophagy. A large part of the C. atys diet consists of the oily nut of Sacoglottis gabonensis, which is accessed by post-canine crushing of the hard, protective seed coat. During a typical foraging bout, some seeds are discarded after initial crushing attempts using isometric biting, but the reason mangabeys reject some seeds and break into others is unclear. Although C. atys is sexually dimorphic, little is known about whether differences between males and females affect the selectivity of mechanically protected foods. We studied C. atys feeding on S. gabonensis in the Taï National Park,  Côte d'Ivoire, in July and August 2016. Nuts discarded after an initial crushing attempt were collected and their hardness measured using a Shore D durometer. Measurements were taken in the region of the nut where monkeys attempted to crush it. Hardness values of nuts rejected by adult male (n = 79) and adult female (n = 104) C. atys were compared to those of a control assemblage of nuts collected randomly on the forest floor (n = 69). Nuts rejected by either sex do not differ statistically from the random sample; however, they do differ from each other, with females rejecting harder nuts. This suggests that males are more effective at broaching harder seed husks, and discard seeds based on other factors.

Anthrax is a worldwide zoonotic disease caused by the spore-forming bacterium Bacillus anthracis . Primarily a disease of herbivores, human infections often result from direct contact with contaminated animal products (cutaneous and inhalational anthrax) or through consumption of infected meat (gastrointestinal anthrax). The genetic near neighbor, Bacillus cereus biovar anthracis (Bcbva), causes an anthrax-like illness in the wildlife and livestock of west and central Africa due to the presence and expression of B. anthracis -specific virulence factors in this background. While Bcbva infections have not been reported in humans, a recent seroprevalence study detected Bcbva antibodies in the rural population around Taï National Park. This work describes the development of new TaqMan multiplex PCRs for the simultaneous detection of B. anthracis and Bcbva. The assays are designed to amplify Ba-1, capB , and lef markers in B. anthracis and genomic island IV (GI4), capB , and lef in Bcbva. Our assays allow for the rapid discrimination of B. anthracis and Bcbva and will provide insights into the molecular epidemiology of these two important pathogens that share an overlapping geographical range in west and central Africa.

We review feeding and mandibular anatomy in a community of West African monkeys. We use field observations, food material property data, and skeletal specimens from the Ivory Coast's Taï Forest to explore the factors that shape mandibular architecture in colobines and cercopithecines. Despite excellent geographic control across our sample, the fit between bone form (as conventionally described) and functional activity (as we perceive it) is not spectacular. We present a thought experiment to assess how well we could reconstruct diet in the Taï monkeys if we only had skeletons and teeth to study. This exercise indicated that we would be correct about half the time. Our analyses reinforce the notion that diet is anything but a monolithic variable and that better success at relating mandibular form to food must incorporate information on ingestive and processing behavior, geometric and material properties of foods, and both material and structural data on jaws themselves., (© 2019 Wiley Periodicals, Inc.)

Primates are hypothesized to "fall back" on challenging-to-process foods when preferred foods are less available. Such dietary shifts may be accompanied by changes in oral processing behavior argued to be selectively important. Here, we examine the oral processing behavior of Diana monkeys (Cercopithecus diana) in the Taï Forest across their dietary breadth, testing relationships among food intake, fruit availability, preference, and oral processing behaviors including those involved in food ingestion and breakdown. We conducted 1,066 focal follows from April 2016 to September 2017 documenting frequencies of incisor, canine, and cheek tooth mastications (i.e., chews) per ingestive action (n = 11,906 feeding events). We used phenological survey and scan sample data collected between 2004 and 2009 to examine dietary preference and food availability. Our analyses show that Diana monkeys processed foods in significantly different ways (H2 = 360.8, p < 0.001), with invertebrates requiring the least oral processing, fruit requiring intermediate amounts, and leaves requiring the most oral processing. There was no relationship between fruit availability and consumption of preferred or nonpreferred fruits (p > 0.05); however, preferred fruits were processed with significantly fewer mastications (i.e., less chewing) than nonpreferred fruits (U = 6,557, p < 0.001). We thus demonstrate that, when preferred foods are scarce, Diana monkeys do not fall back on difficult-to-process foods. Changes in processing profiles occurred throughout the year and not solely when preferred foods were in short supply. Though preferred fruits required less processing than nonpreferred fruits, we found no relationship between fruit preference and fruit availability. Diana monkeys' lack of readily identifiable fallback foods may be attributable to the relatively high tree diversity and productivity of the Taï Forest. We conclude that Diana monkeys engage in resource switching, consuming a relatively easy-to-process diet year-round., (© 2020 S. Karger AG, Basel.)

One way bone adapts to its mechanical environment is by Haversian remodeling, a repair process in which existing bone is resorbed and replaced by new bone. Haversian remodeling forms interconnected, cylindrical structures called secondary osteons. The amount of remodeling that occurs is related to the nature of mechanical loading and accrual of microdamage, but it is uncertain whether habitual loads of high magnitude versus high frequency result in more remodeling. The answer to this question is important if remodeling is to be a tool for inferring loading environments, and thus behavior, in past populations. Here, secondary osteon population density (OPD), osteon cross-sectional area (On.Ar), and percent Haversian bone (%HAV) were compared among mid-diaphysis femora, tibia, fibulae, and mid-level ribs of five adult crab-eating macaques (Macaca fascicularis). Ribs experience relatively low strains but have a high daily loading frequency (~33 times per minute). Limb bones are loaded for fewer cycles per day, but the femur and tibia have high load magnitudes due to gravitational forces. Strain magnitudes in the fibula are a fraction of those in the femur and tibia. Analyses of variance demonstrated significant differences in OPD (P = 0.010) and On.Ar (P < 0.001) among the bones. Pairwise t-tests revealed greater OPD but lower On.Ar in the rib than all other bones. The high rib OPD suggests that Haversian remodeling is more responsive to load frequency than strain magnitude. The fact that osteons are smaller in ribs than any other bone may be an effect of remodeling in comparatively narrow cortices., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Limb bone articular and diaphyseal proportions have been shown to relate to locomotor behavior in broad comparisons across catarrhines, but comparisons among phylogenetically and functionally more closely related species may be particularly useful in investigating form-function relationships that can be applied to fossil taxa. Here we compare inter- and intra-limb proportions of diaphyseal strength and articular surface area and breadth of the femur and humerus with frequencies of leaping and vertical climbing behavior in 13 cercopithecid species. Leaping frequency is highly positively correlated with femoral/humeral diaphyseal strength, moderately positively correlated with femoral/humeral articular breadth, and less highly correlated with femoral/humeral articular surface area. These results are consistent with predicted higher bending loads as well as joint reaction forces on the femora of leapers. Surface areas may show a weaker association because they also directly impact joint excursion and are thus more influenced by other aspects of locomotion, including climbing. Climbing frequency is positively correlated with humeral head articular surface area/diaphyseal strength, but weakly negatively correlated with femoral head articular surface area/diaphyseal strength. These combined trends lead to a strong negative association between climbing and femoral/humeral head surface area. Femoral/humeral diaphyseal strength and distal articular breadth are not correlated with climbing frequency. The climbing results are consistent with greater shoulder mobility in more frequent vertical climbers. The lack of such a relationship in the femur among these taxa contrasts with earlier findings for catarrhines more generally, including hominoids, and may be a result of different climbing kinematics in cercopithecoids involving less hip abduction than in hominoids. Different use of the forelimb during climbing in cercopithecoids and hominoids may also explain the lack of association between femoral/humeral diaphyseal strength and climbing in the present study, in contrast to comparisons across catarrhines more generally., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Bone remodeling is at least partially mediated by the mechanical environment created by an animal's behavior. Here, we test the hypothesis that bone remodeling is primarily induced by high magnitude loads, likely encountered during leaping/bounding behaviors. Osteon population density (OPD), osteon cross-sectional area (On.Ar), and relative osteonal area (%HAV) were measured from femoral and humeral midshaft thin sections of four cercopithecids (N = 5 per species) from Taï Forest, Côte d'Ivoire: Colobus polykomos, Piliocolobus badius, Cercopithecus diana, and Cercocebus atys. All species are generalized quadrupeds but vary in leaping frequency and overall activity budget. Differences between taxa with high (C. polykomos and P. badius) and low leaping frequency (C. diana and C. atys) were assessed via a phylogenetically informed generalized linear mixed model using Markov Chain Monte Carlo methods. Femoral OPD and %HAV are greater in the high frequency leapers than in low frequency leapers, suggesting that frequent high magnitude loads engender remodeling, however, there is no similar pattern in the humerus, which presumably also experiences high magnitude loads during leaping. Additionally, OPD and %HAV are greater in the humerus than the femur, despite load magnitude being presumably higher in the femur. These results provide conflicting support for hypotheses about load magnitude and load frequency as they relate to bone remodeling activity. Future work is proposed to parse out the respective effects of load magnitude and frequency on bone remodeling. Anat Rec, 302:1116-1126, 2019. © 2018 Wiley Periodicals, Inc., (© 2018 Wiley Periodicals, Inc.)

Objectives: The relationship between radiographic grayscale and elastic modulus was determined using mandibular cortical bone of colobine monkeys. Quantification of this relationship is critical for establishing absolute measures of structural rigidity of skeletal elements., Materials and Methods: We determined the Vickers microhardness values in mandibular bone from two species of African colobine monkeys and related these values to elastic modulus through an empirically determined correlation. We also determined radiographic grayscale values from microcomputed tomographic scans of the mandible in the same regions in which microhardness was sampled. We then correlated modulus to grayscale with a power law relationship., Results: We found that elastic modulus scaled with negative allometry with respect to grayscale with an exponent of 0.77., Discussion: Our results suggest a single exponent can effectively capture the relationship of grayscale to elastic modulus and facilitate development of heterogeneous structural models for use in comparative and computational biomechanical studies., (© 2017 Wiley Periodicals, Inc.)

Objectives: We investigated how heterogeneity in material stiffness affects structural stiffness in the cercopithecid mandibular cortical bone. We assessed (1) whether this effect changes the interpretation of interspecific structural stiffness variation across four primate species, (2) whether the heterogeneity is random, and (3) whether heterogeneity mitigates bending stress in the jaw associated with food processing., Materials and Methods: The sample consisted of Taï Forest, Cote d'Ivoire, monkeys: Cercocebus atys, Piliocolobus badius, Colobus polykomos, and Cercopithecus diana. Vickers indentation hardness samples estimated elastic moduli throughout the cortical bone area of each coronal section of postcanine corpus. For each section, we calculated maximum area moment of inertia, I max (structural mechanical property), under three models of material heterogeneity, as well as spatial autocorrelation statistics (Moran's I, I MORAN )., Results: When the model considered material stiffness variation and spatial patterning, I max decreased and individual ranks based on structural stiffness changed. Rank changes were not significant across models. All specimens showed positive (nonrandom) spatial autocorrelation. Differences in I MORAN were not significant among species, and there were no discernable patterns of autocorrelation within species. Across species, significant local I MORAN was often attributed to proximity of low moduli in the alveolar process and high moduli in the basal process., Discussion: While our sample did not demonstrate species differences in the degree of spatial autocorrelation of elastic moduli, there may be mechanical effects of heterogeneity (relative strength and rigidity) that do distinguish at the species or subfamilial level (i.e., colobines vs. cercopithecines). The potential connections of heterogeneity to diet and/or taxonomy remain to be discovered., (© 2016 Wiley Periodicals, Inc.)

Fossils attributed to Australopithecus sediba are described as having phylogenetic affinities with early Homo to the exclusion of other South African australopiths. With respect to functional anatomy of mastication, one implication of this hypothesis is that A. sediba mandibles should exhibit absolutely and relatively reduced stiffness and strength in comparison to Australopithecus africanus and Paranthropus robustus jaws. Examination of cortical bone distribution in the MH 1 and MH 2 mandibles of A. sediba (evaluated against samples of Pan, early and modern Homo as well as A. africanus and P. robustus) indicate that the A. sediba mandibular corpus was geometrically similar to other South African australopiths. In particular, enhanced torsional rigidity is characteristic of all South African australopiths including A. sediba. These findings are consistent with a hypothesis that masticatory mechanics may have been similar to other australopiths (and distinct from exemplars of early Homo), and as such suggest that A. sediba's mandibles were functionally suited to consume hard and tough objects. Recent mechanical modeling of the A. sediba cranium, however, has been interpreted as indicating that this species was relatively poorly adapted to produce large bite forces and likely experienced relatively modest strains in its facial skeleton. This paradox - that the cranium signals a departure from the australopith morphotype whereas the mandibles conform to a hypodigm of australopith grade - can be resolved, in part, if it is acknowledged that mechanical performance variables offer imperfect insight into what constitutes feeding adaptations., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Objectives: Independent lines of evidence suggest that osteonal bone remodeling is a function of both mechanical (i.e., changes in stress) and non-mechanical (i.e., metabolic needs related to calcium liberation) factors. The degree to which secondary bone reflects mechanical factors, however, is incompletely understood despite the common assumption that the stress environment mediates remodeling activity. Here, we investigate whether there are remodeling differences between regions of primate mandibular bone known to have distinct stress environments., Methods: Osteon density, osteon fragment density, and relative osteonal area are measured as indicators of remodeling activity from postcanine and symphyseal thin sections of four sympatric monkey species (N = 20 total) from Taï Forest, Côte d'Ivoire: Piliocolobus badius, Colobus polykomos, Cercocebus atys, Cercopithecus diana. Subfamily and regional effects were assessed by two-way ANOVA., Results: Symphyseal bone has lower osteonal density, fragment density and relative osteonal area than postcanine bone in all species, indicating relatively low remodeling activity in symphyseal bone, despite the likelihood of relatively high stresses in its lingual cortex. Subfamily differences in postcanine remodeling are significant in that colobines exhibit greater remodeling than cercopithecines., Discussion: The data suggest that high strains are not requisite for bone remodeling. How the lingual symphysis negotiates a high strain environment without the reparative benefit of remodeling is yet to be elucidated, but the data prompt reevaluation of the relationship of targeted remodeling to stress histories. Differences in osteonal bone density between taxa might reflect feeding or dietary influences on remodeling activity, but sample composition prevents parsing behavioral from other taxon-specific effects., (© 2016 Wiley Periodicals, Inc.)

Experimental analyses directly inform how an anatomical feature or complex functions during an organism's lifetime, which serves to increase the efficacy of comparative studies of living and fossil taxa. In the mammalian skull, food material properties and feeding behaviour have a pronounced influence on the development of the masticatory apparatus. Diet-related variation in loading magnitude and frequency induce a cascade of changes at the gross, tissue, cellular, protein and genetic levels, with such modelling and remodelling maintaining the integrity of oral structures vis-à-vis routine masticatory stresses. Ongoing integrative research using rabbit and rat models of long-term masticatory plasticity offers unique insight into the limitations of functional interpretations of fossilised remains. Given the general restriction of the palaeontological record to bony elements, we argue that failure to account for the disparity in the hierarchical network of responses of hard versus soft tissues may overestimate the magnitude of the adaptive divergence that is inferred from phenotypic differences. Second, we note that the developmental onset and duration of a loading stimulus associated with a given feeding behaviour can impart large effects on patterns of intraspecific variation that can mirror differences observed among taxa. Indeed, plasticity data are relevant to understanding evolutionary transformations because rabbits raised on different diets exhibit levels of morphological disparity comparable to those found between closely related primate species that vary in diet. Lastly, pronounced variation in joint form, and even joint function, can also characterise adult conspecifics that differ solely in age. In sum, our analyses emphasise the importance of a multi-site and hierarchical approach to understanding determinants of morphological variation, one which incorporates critical data on performance., (© 2015 Cambridge Philosophical Society.)

Objective: The etiology of dental microwear is incompletely understood, despite copious documentation of wear patterns from wild and captive specimens across numerous vertebrate taxa. Among the contested issues with respect to microwear formation is the question of whether materials softer than enamel (specifically, foods themselves) can produce wear features., Design: We examine the creation of enamel microwear features in vitro from foods that vary in hardness and toughness on a sample of mammalian lower molars (pig, bear, deer, and primate). These experiments involved applying loads at a constant displacement rate perpendicular to an occlusal enamel surface. Changes in surface microwear textures were assessed after 10 loads., Results: Our experiments demonstrate that even relatively soft foods free of exogenous abrasives modify surface texture to produce distinctive microwear fabrics. Consequently, these data provide clear evidence that materials softer than enamel are capable of indenting and abrading enamel surfaces. Foods with a relatively high elastic modulus are associated with larger and more extensive microwear features, although the relationship between food stiffness and rate of microwear formation does not appear to be a simple one., Conclusions: These observations refute recent arguments that food material is an insignificant agent in the formation and accumulation of enamel microwear. Relative hardness of ingested materials is only one factor in the etiology of microwear formation., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

We collected frequency data on oral processing behaviors during feeding in habituated groups of Western red colobus, Piliocolobus badius, and Western black and white, Colobus polykomos, ranging in the Ivory Coast's Tai National Park. During the sampling period, the diet of red colobus consisted of approximately 75% leaves compared to approximately 47% leaves and buds in black and white colobus. Black and white colobus chewed more frequently per ingestive event than did red colobus. Black and white colobus also employed their anterior teeth much more frequently than did red colobus, a difference attributed to the frequent consumption by C. polykomos of Pentaclethra macrophylla seeds and pods. A material analysis of these food items reveals that both the seed coating and seed flesh are quite soft; however, the pod housing the seeds is very tough. We argue that the pod's toughness, geometry, and fiber orientation collectively result in a food that is very difficult to process, resulting in long handling times and frequent, aggressive use of the incisors. We compare these data with those collected on another Tai primate-the sooty mangabey, Cercocebus atys-and demonstrate that during feeding, both colobine species use their incisors less than the mangabey, but that the cercopithecine chews less than either colobine. Combining data on oral processing behaviors with those on the material properties of items being ingested should lead to more informed interpretations of dentognathic morphology., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Objectives: This research theoretically models and empirically records symphyseal surface strain during in vitro human mandibular wishboning (lateral transverse bending) in order to test one aspect of the hypothesis that the chin is an adaptive response to masticatory stresses. From a perspective of optimality, three questions were tested: 1) Do human mandibles function as curved beams during wishboning? 2) Is the presence of a chin associated with lower than predicted curved beam effects? 3) Are there relatively low strain gradients on the lingual and labial symphyseal surfaces respectively?, Materials and Methods: Based on morphometric criteria, theoretical wishboning strains were calculated for five dentate adult human mandibles. The same mandibles were fitted with strain gauges and subjected to simulated wishboning loads. From the empirically-recorded strains, relative strains were calculated by dividing all strains by the absolute lowest strain in a given specimen. The theoretical and empirical results were compared in order to address the three related questions guiding this research., Results: Human mandibles behave as curved beams during wishboning (question 1). Empirical strain measures showed greater disparity both between and within the labial and lingual symphyseal surfaces than the theoretical models predictions (questions 2 and 3)., Discussion: Human symphyseal form, with its distinctive chin, is unlikely to be adapted for countering wishboning loads. Chins are associated with larger than expected strain gradients within and between symphyseal surfaces, which runs counter to the optimality criterion typically invoked in assessing trait performance for signs of adaptation. The implications are twofold: 1) wishboning may not, in fact, be a regular feature of human mastication or 2) wishboning may not pose the same structural risks in human jaws as this load does in other anthropoid primates., (© 2015 Wiley Periodicals, Inc.)

Although modern humans are considered to be morphologically distinct from other living primates because of our large brains, dexterous hands, and bipedal gait, all of these features are found among extinct hominins. The chin, however, appears to be a uniquely modern human trait. Probably because of the chin's exclusivity, many evolutionary scenarios have been proposed to explain its origins. To date, researchers have developed adaptive hypotheses relating chins to speech, mastication, and sexual selection; still others see it as a structural artifact tangentially related to complex processes involving evolutionary retraction of the midfacial skeleton. Consensus has remained elusive, partly because hypotheses purporting to explain how this feature developed uniquely in modern humans are all fraught with theoretical and/or empirical shortcomings. Here we review a century's worth of chin hypotheses and discuss future research avenues that may provide greater insight into this human peculiarity., (© 2016 Wiley Periodicals, Inc.)

Objective: Procolobus badius, Colobus polykomos, and Cercocebus atys are three West African primate species known to have distinctive feeding behaviors. Our objectives were (1) to test whether intra-taxon variation in bone mineral content exists between anterior and posterior regions of the mandible and (2) to determine if interspecific differences are interpretable via feeding and dietary idiosyncracies among the three taxa., Design: Twenty-one mandibles from naturally deceased C. polykomos (n=7), P. badius (n=9), and C. atys (n=5) were scanned using cone beam computerized tomography. Alveolar bone (AB) and basal cortical bone (CB) of incisor (I1) and second molar (M2) regions were digitally isolated. Degree of bone mineralization (DBM) distribution was obtained using histograms of CT attenuation values. Mean, standard deviation (SD), the 5th (Low5) and the 95th (High5) percentiles of the DBM histogram were compared between the jaw regions in species., Results: The mean and Low5 of DBM were significantly lower for AB than CB of all species (p<0.001). The AB DBM parameters were not significantly different between I1 and M2 of all species (p>0.056) except the mean of C. polykomos (p<0.05). The mean, SD, High5 of CB DBM at M2 of C. atys was significantly higher than those of C. polykomos and P. badius (p<0.006)., Conclusions: The durophagous C. atys had higher CB DBM value at the M2 region than C. polykomos and P. badius, which supports the hypothesis that materially stiffer mandibular bone in C. atys can develop in response to the generation of high bite forces during hard object feeding., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Microbiological degradation is one of the most important factors responsible for the destruction of bone in archaeological contexts. Microscopic focal destruction (MFD) is the most prevalent form of microbial tunneling and is encountered very commonly in human bones from archaeological sites, whereas animal bones from these same sites show significantly better preservation if they were deposited in a fragmentary (e.g., butchered) state. Similarly, most fossils show either no evidence or only minor traces of bacterial osteolysis. These observations and experimental evidence point to an endogenous origin for osteolytic bacteria, suggesting that bone bioerosion could potentially aid in reconstructing early taphonomic events. We here report extensive MFD in the mandibular corpus of a small (presumptive female) individual of the hominin Paranthropus robustus from the Early Pleistocene site of Swartkrans, South Africa. The specimen (SKX 5013) derives in situ from the Member 2 deposit, which is dated to ca. 1.5-1.0 Ma. Examination of sections from the corpus by backscattered electron microscopy reveals numerous small linear longitudinal and budded tunneling cavities, which tend to be concentrated around Haversian canals and are more abundant closer to the endosteal aspect of the section. The taphonomy of Swartkrans has been the subject of intense investigation, and given the possibility that different agents of accumulation may have been responsible for the faunal and hominin fossils in the different members at the site, the observation that a specimen of P. robustus from Member 2 displays significant microbial osteolysis is of potential interest. A study of the prevalence of this process in adequately large samples of the animal bones from these units may yield novel insights and provide refinement of our understanding of their taphonomic histories. Such observations might well reveal differences among the various members that could provide another valuable source of osteoarchaeological information for the site., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Elastic modulus of bone from the anterior mandibular corpus was determined via microindentation in a mixed-sex ontogenetic sample (N = 14) of Macaca fascicularis. This investigation focused on the hypothesis that material heterogeneity in the macaque mandibular symphysis-provided an accounting of age and sex variation-is explicable as a means to homogenize strains in this region. Experimental data and theoretical models of masticatory loading indicate that in the absence of material compensation, large strain gradients exist in the anterior mandibular corpus of macaques, particularly between lingual and labial cortical plates owing to the effects of lateral transverse bending. Microindentation data indicate that juvenile macaques possess less stiff bone than their subadult and adult counterparts; however, sex differences in elastic modulus are not apparent. Anisotropy variation is idiosyncratic; that is, there is not a common pattern of variation in stiffness sampled among orthogonal planes across individuals. Similarly, differences in stiffness between lingual and labial cortical plates, as well as differences among alveolar, midcorpus, and basal regions are inconsistently observed. Consequently, we find little evidence in support of the hypothesis that spatial variation in bone stiffness functions to homogenize strains in the anterior corpus; in fact, in some individuals, this spatial variation serves to exacerbate, rather than to minimize, strain gradients. The mechanical benefit of elastic modulus variation in the macaque mandibular symphysis is unclear; this variation may not confer adaptive benefit in terms of structural integrity despite the fact that such variation has discernible functional consequences., (© 2014 Wiley Periodicals, Inc.)

We present information on food hardness and monthly dietary changes in female sooty mangabeys (Cercocebus atys) in Tai Forest, Ivory Coast to reassess the hypothesis that thick molar enamel is parsimoniously interpreted as a response to consumption of hard foods during fallback periods. We demonstrate that the diet of sooty mangabeys varies seasonally, but that one food--Sacoglottis gabonensis--is the most frequently consumed food every month and year round. This food is the hardest item in the sooty diet. Given that this species has among the thickest enamel within the primate order, a plausible conclusion is that thick enamel in this taxon evolved not in response to seasonally critical function or fallback foods, but rather to the habitual, year round processing of a mechanically protected foodstuff. These data serve as a caution against de rigueur interpretations that reliance on fallback foods during lean periods primarily explains the evolution of thick enamel in primates., (© 2014 Wiley Periodicals, Inc.)

Primate canines function in social displays but are also recruited for biting in agonistic encounters. Although the precise nature of the loads such behavior places on the canine crown is unknown, it is thought that bending is a major component of such loads. To date, modeling of canine bending strength has relied on idealized geometric representations. Accounting for the tapering of the crown as well as shape changes along an apical-basal axis provides a more realistic model for assessment of bending stress in canines. We provide such an accounting and evaluate the hypothesis that the morphology of the cercopithecoid canine represents a structural solution for maintaining constant maximum bending stress under apical or distributed loading in a parasagittal plane. This isostress hypothesis is analogous to a design criterion of minimum mass for a given structural requirement. Examining permanent maxillary canines from males and females representing eight West African cercopithecoid species, we reconstructed crown geometry from apex to base using microcomputed tomography. From reconstructed cross-sections, we determined section moduli about a buccolingual centroidal axis. We then determined what the taper should be for a variety of parasagittal loading distributions if the isostress hypothesis were true and compared these theoretical tapers to actual crown geometry. We found that a variety of loading distributions can be accommodated by the canines, particularly among males. These results suggest that our sample of canines are not optimized for resisting particular biting loads, but effectively limit stress gradients associated with a range of behaviors., (Copyright © 2014 Wiley Periodicals, Inc.)

The hypodigm of Homo floresiensis from the cave of Liang Bua on Flores Island in the archipelago of Indonesia includes two mandibles (LB1/2 and LB6/1). The morphology of their symphyses and corpora has been described as sharing similarities with both australopiths and early Homo despite their Late Pleistocene age. Although detailed morphological comparisons of these mandibles with those of modern and fossil hominin taxa have been made, a functional analysis in the context of masticatory biomechanics has yet to be performed. Utilizing data on cortical bone geometry from computed tomography scans, we compare the mechanical attributes of the LB1 and LB6 mandibles with samples of modern Homo, Pan, Pongo, and Gorilla, as well as fossil samples of Paranthropus robustus, Australopithecus africanus and South African early Homo. Structural stiffness measures were derived from the geometric data to provide relative measures of mandibular corpus strength under hypothesized masticatory loading regimes. These mechanical variables were evaluated relative to bone area, mandibular length and estimates of body size to assess their functional affinities and to test the hypothesis that the Liang Bua mandibles can be described as scaled-down variants of either early hominins or modern humans. Relative to modern hominoids, the H. floresiensis material appears to be relatively strong in terms of rigidity in torsion and transverse bending, but is relatively weak under parasagittal bending. Thus, they are 'robust' relative to modern humans (and comparable with australopiths) under some loads but not others. Neither LB1 nor LB6 can be described simply as 'miniaturized' versions of modern human jaws since mandible length is more or less equivalent in Homo sapiens and H. floresiensis. The mechanical attributes of the Liang Bua mandibles are consistent with previous inferences that masticatory loads were reduced relative to australopiths but remained elevated relative to modern Homo., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Evidence is accumulating that bone material stiffness increases during ontogeny, and the role of elastic modulus in conditioning attributes of strength and toughness is therefore a focus of ongoing investigation. Developmental changes in structural properties of the primate mandible have been documented, but comparatively little is known about changes in material heterogeneity and their impact on biomechanical behavior. We examine a cross-sectional sample of Macaca fascicularis (N = 14) to investigate a series of hypotheses that collectively evaluate whether the patterning of material stiffness (elastic modulus) heterogeneity in the mandible differs among juvenile, subadult and adult individuals. Because differences in age-related activity patterns are known to influence bone stiffness and strength, these data are potentially useful for understanding the relationship between feeding behavior on the one hand and material and structural properties of the mandible on the other. Elastic modulus is shown to be spatially dependent regardless of age, with this dependence being explicable primarily by differences in alveolar versus basal cortical bone. Elastic modulus does not differ consistently between buccal and lingual cortical plates, despite likely differences in the biomechanical milieu of these regions. Since we found only weak support for the hypothesis that the spatial patterning of heterogeneity becomes more predictable with age, accumulated load history may not account for regional differences in bone material properties in mature individuals with respect to the mandibular corpus., (Copyright © 2013 Wiley Periodicals, Inc.)

This study tests the hypothesis that vertical habitat preferences of different monkey species inhabiting closed canopy rainforest are reflected in oxygen isotopes. We sampled bone from seven sympatric cercopithecid species in the Taï forest, Côte d'Ivoire, where long-term study has established taxon-specific patterns of habitat use and diet. Modern rib samples (n = 34) were examined for oxygen (δ(18)Oap) and carbon (δ(13)Cap) from bone apatite ('bioapatite'), and carbon (δ(13)Cco) and nitrogen (δ(15)Nco) from bone collagen. Results are consistent for C3 feeders in a closed canopy habitat. Low irradiance and evapotranspiration, coupled with high relative humidity and recycled CO2 in forest understory, contribute to observed isotopic variability. Both δ(13)Cco and δ(13)Cap results reflect diet; however, δ(13)C values are not correlated with species preference for canopy height. By contrast, δ(18)Oap results are correlated with mean observed height and show significant vertical partitioning between taxa feeding at ground, lower and upper canopy levels. This oxygen isotope canopy effect has important palaeobiological implications for reconstructing vertical partitioning among sympatric primates and other species in tropical forests.

Inference of feeding adaptation in extinct species is challenging, and reconstructions of the paleobiology of our ancestors have utilized an array of analytical approaches. Comparative anatomy and finite element analysis assist in bracketing the range of capabilities in taxa, while microwear and isotopic analyses give glimpses of individual behavior in the past. These myriad approaches have limitations, but each contributes incrementally toward the recognition of adaptation in the hominin fossil record. Microwear and stable isotope analysis together suggest that australopiths are not united by a single, increasingly specialized dietary adaptation. Their traditional (i.e., morphological) characterization as "nutcrackers" may only apply to a single taxon, Paranthropus robustus. These inferences can be rejected if interpretation of microwear and isotopic data can be shown to be misguided or altogether erroneous. Alternatively, if these sources of inference are valid, it merely indicates that there are phylogenetic and developmental constraints on morphology. Inherently, finite element analysis is limited in its ability to identify adaptation in paleobiological contexts. Its application to the hominin fossil record to date demonstrates only that under similar loading conditions, the form of the stress field in the australopith facial skeleton differs from that in living primates. This observation, by itself, does not reveal feeding adaptation. Ontogenetic studies indicate that functional and evolutionary adaptation need not be conceptually isolated phenomena. Such a perspective helps to inject consideration of mechanobiological principles of bone formation into paleontological inferences. Finite element analysis must employ such principles to become an effective research tool in this context., (Copyright © 2013 Wiley Periodicals, Inc.)

Studies of dental macrowear can be useful for understanding masticatory and ingestive behavior, life history, and for inferring dietary information from the skeletal material of extinct and extant primates. Such studies to date have tended to focus on one or two teeth, potentially missing information that can be garnered through examination of wear patterns across the tooth row. Our study measured macrowear in the postcanine teeth of three sympatric cercopithecid species from the Taï Forest, Côte d'Ivoire (Cercocebus atys, Procolobus badius, and Colobus polykomos), whose diets have been well-described. Inter-specific analyses suggest that different diets and ingestive behaviors are characterized by different patterns of wear across the molar row, with Cercocebus atys emphasizing tooth use near P4 -M1 , P. badius emphasizing a large amount of tooth use near M2 -M3 , and Colobus polykomos exhibiting wear more evenly across the postcanine teeth. Information regarding differential tooth use across the molar row may be more informative than macrowear analysis of isolated teeth for making inferences about primate feeding behavior., (Copyright © 2013 Wiley Periodicals, Inc.)

Traditionally, thick enamel has often been used to infer durophagy (i.e., hard nut and seed consumption) in extinct hominins. These inferences are based on the hypothesis that thick enamel is primarily an adaptation to prevent tooth fracture or chipping resulting from high-stress loads produced during the mastication of large hard foods. An alternative view argues that thick enamel may aid in maintaining tooth function in the face of gradual dental wear from grit, phytoliths and acid, which may be found in foods of widely varying hardness. We use estimates of primate dietary abrasiveness and recorded lifespan to test the hypothesis that enamel thickness is selectively responsive to lifetime dental wear resistance. We use data from the literature to relate enamel thickness to measures of dietary abrasiveness, diet profiles, and longevity for 17 primate species and performed linear regression using several combinations of these variables. We found a positive association between lifetime dietary wear and enamel thickness, suggesting that thick molar enamel in primates may have evolved as a means to resist wear apart from selection to resist tooth fracture. Assuming our estimates of lifetime dietary wear are accurate, we caution against ascribing thick enamel solely to the presence of hard-object feeding in paleoanthropological contexts without also considering primate lifespan and other aspects of feeding ecology., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The documentation of enamel thickness variation across primates is important because enamel thickness has both taxonomic and functional relevance. The Old World monkeys commonly referred to as mangabeys have figured prominently in investigations of feeding ecology and enamel thickness. In this article, we report enamel thickness values for four mangabey taxa (Cercocebus atys, Cercocebus torquatus, Lophocebus aterrimus, and Lophocebus albigena), offer revised interpretation of the significance of thick enamel in papionin evolution, and place our new data in a broader comparative framework. Our data indicate that all mangabeys have thick enamel and that the values obtained for Cercocebus and Lophocebus equal or exceed those published for most extant non-human primates. In addition, new field data combined with a current reading of the dietary literature indicate that hard foods make up a portion of the diet of every mangabey species sampled to date. Clarification on the relationship between diet and enamel thickness among mangabeys is important not only because of recognition that mangabeys are not a natural group but also because of recent arguments that explain thick enamel as an evolved response to the seasonal consumption of hard foods., (Copyright © 2011 Wiley Periodicals, Inc.)

Researchers have increasingly recognized the need to quantify the material properties of primate food items, particularly hardness (H) and stiffness (E), which is measured as elastic modulus. Assessing E in the field is particularly difficult because the typical equipment needed to perform the requisite analyses is expensive and cumbersome. Alternatively, researchers can use hand-held, relatively inexpensive, portable durometers that measure H on Shore scales. Shore-D durometers show a reliable ability to characterize H in harder-stiffer materials, and Shore-D measures in these materials can be reliably converted to E. Shore-A durometers-employed in past field studies of food properties-do not accurately characterize the properties of harder-stiffer materials, which are likely to be those materials exerting the greatest mechanical demands on primate masticatory morphology. We offer recommendations for Shore-D durometer usage in the field., (2011 Wiley Periodicals, Inc.)

Alveolar bone has several mechanical functions, including tooth support and accommodation of occlusal and other masticatory forces. Its unique functional-mechanical environment is reflected by its structural characteristics, but whether alveolar bone is materially distinct from bone elsewhere in the primate facial skeleton is uncertain. This uncertainty is attributable not only to a limited amount of data but also to conflicting findings among these data. We evaluated elastic modulus variation in the mandibular corpus of eight adult specimens of the monkeys Procolobus badius and Colobus polykomos via microindentation to evaluate whether alveolar bone is more compliant than basal bone and to quantify patterns of variation between sexes and species. We sampled Vickers hardness from six serial transverse sections and one coronal section from both the alveolar process and the basal corpus. Hardness values were converted to elastic modulus via regressions specific for bone tissue. Analysis of variance reveals that a plurality of variation is found on a regional scale; i.e., alveolar bone is more compliant than adjacent basal bone. Species affiliation and sex are not significant sources of variation. These findings support a hypothesis that compliance of alveolar bone represents a material solution for avoiding large stress concentrations arising from occlusal loads. Other comparative data suggest important differences between colobine and cercopithecine mandibles in terms of bone stiffness, both overall and in terms of relative stiffness of alveolar and basal cortical bone., (Copyright © 2010 Wiley-Liss, Inc.)

Alveolar bone is functionally involved with tooth support and must also be competent in accommodating masticatory forces. Data from a variety of perspectives--including observations of anatomy, metabolic activity and determination of mechanical properties--suggest that alveolar bone is more compliant than the more inferiorly situated basal bone of the mandibular corpus. The nature of stiffness variation within the alveolar process, however, remains largely unexplored. The technique of microindentation is used to estimate bone stiffness variation in the cortical alveolar bone of a sample of eight adult mandibles from two species of West African colobus monkeys. The null hypothesis under investigation is that bone stiffness variation in the alveolar process is random with respect to species, sex, and location. Alternative hypotheses are evaluated with respect to species, sex and locality effects, including those associated with cortical thickness variation and masticatory loading. Microindentation data do not indicate species or sex differences. Spatial variation in alveolar bone, however, is nonrandom. The stiffest bone is localized in the superior alveolar process, and significant differences between buccal and lingual cortical plates are found in five of eight specimens. Evidence for a superoinferior stiffness gradient is found in half the specimens but is confined to either the buccal or lingual cortical plate. Covariation between bone stiffness and bone thickness is weak. Relative compliance of the alveolar process represents a biomechanical solution for enhancing toughness of cortical bone. The relationship of the spatial patterning of bone stiffness to the masticatory loading environment is unclear., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Members of the Cercocebus-Mandrillus clade are united by several morphological features, including expanded premolars which are argued to be associated with a preponderance of hard objects in the diet. We test the association between premolar expansion and hard object feeding by examining how different dental regions are used during food processing. We examined the diet and oral processing activities of sooty mangabeys (Cercocebus atys) in the Ivory Coast's Tai forest from August 2008 to September 2009. In addition to compiling diet profiles, we recorded the frequency that individuals performed four activities: 1) incising, 2) canine puncturing/scraping, 3) postcanine crushing (i.e., isometric biting), and 4) routine mastication (chewing cycles). Sooty mangabeys have a relatively narrow diet that consists largely of nuts/seeds, fruits, and invertebrates. While there are age and sex differences in diet, the most frequently consumed foods are similar across age and sex classes. The most frequently consumed foods are seeds of Sacoglottis gabonensis which are the hardest items in the sooty mangabey diet. Patterns of ingestive behavior vary with food type, but adults and nonadults (excluding infants dependent on mothers) of both sexes process similar foods. Premolar expansion in Cercocebus atys is associated with powerful crushing of hard objects of specific size and durophagy is a constant feature of sooty mangabey feeding ecology throughout ontogeny., (Copyright © 2010 Wiley-Liss, Inc.)

Morphology of the dentofacial complex of early hominins has figured prominently in the inference of their dietary adaptations. Recent theoretical analysis of craniofacial morphology of Australopithecus africanus proposes that skull form in this taxon represents adaptation to feeding on large, hard objects. A modern analog for this specific dietary specialization is provided by the West African sooty mangabey, Cercocebus atys. This species habitually feeds on the large, exceptionally hard nuts of Sacoglottis gabonensis, stereotypically crushing the seed casings using their premolars and molars. This type of behavior has been inferred for A. africanus based on mathematical stress analysis and aspects of dental wear and morphology. While postcanine megadontia, premolar enlargement and thick molar enamel characterize both A. africanus and C. atys, these features are not universally associated with durophagy among living anthropoids. Occlusal microwear analysis reveals complex microwear textures in C. atys unlike those observed in A. africanus, but more closely resembling textures observed in Paranthropus robustus. Since sooty mangabeys process hard objects in a manner similar to that proposed for A. africanus, yet do so without the craniofacial buttressing characteristic of this hominin, it follows that derived features of the australopith skull are sufficient but not necessary for the consumption of large, hard objects. The adaptive significance of australopith craniofacial morphology may instead be related to the toughness, rather than the hardness, of ingested foods.

The masticatory loading regime of lateral transverse bending (wishboning) is hypothesized to be instrumental in the evolution of symphyseal form among primates. The biomechanics of wishboning have largely been inferred by assuming that the mandible behaves as a curved beam under this load; however, the characterization of stress and strain in the anthropoid symphysis has been interpretively challenging. This is due, in part, to both limitations of sampling strain in an in vivo context and the incongruence of beam theory assumptions on the one hand, and the anatomical complexity of mandibular morphology on the other. Utilizing three-dimensional (3D) Digital Image Correlation (DIC), we employ an in vitro approach to characterize the strain field in a sample of colobine mandibles under simulated wishboning loads in order to assess the utility of idealized curved beam models for characterizing strain gradients in symphyseal bone. Conventional theory of curved beams suggest that colobine mandibles should exhibit reduced disparity of labial and lingual stresses relative to papionin primates given differences in overall mandibular architecture. This prediction is borne out by our analysis: whereas macaques experience lingual:labial strain disparities of 3.5:1, the colobine mandibles exhibit ratios on the order of 2-3:1. However, despite the fact that wishboning loads represent a case of asymmetric bending, details of the wishboning strain field do not conform to expected stress distribution under this model., ((c) 2010 Wiley-Liss, Inc.)

Finite element analysis (FEA) is a potentially powerful tool by which the mechanical behaviors of different skeletal and dental designs can be investigated, and, as such, has become increasingly popular for biomechanical modeling and inferring the behavior of extinct organisms. However, the use of FEA to extrapolate from characterization of the mechanical environment to questions of trophic or ecological adaptation in a fossil taxon is both challenging and perilous. Here, we consider the problems and prospects of FEA applications in paleoanthropology, and provide a critical examination of one such study of the trophic adaptations of Australopithecus africanus. This particular FEA is evaluated with regard to 1) the nature of the A. africanus cranial composite, 2) model validation, 3) decisions made with respect to model parameters, 4) adequacy of data presentation, and 5) interpretation of the results. Each suggests that the results reflect methodological decisions as much as any underlying biological significance. Notwithstanding these issues, this model yields predictions that follow from the posited emphasis on premolar use by A. africanus. These predictions are tested with data from the paleontological record, including a phylogenetically-informed consideration of relative premolar size, and postcanine microwear fabrics and antemortem enamel chipping. In each instance, the data fail to conform to predictions from the model. This model thus serves to emphasize the need for caution in the application of FEA in paleoanthropological enquiry. Theoretical models can be instrumental in the construction of testable hypotheses; but ultimately, the studies that serve to test these hypotheses - rather than data from the models - should remain the source of information pertaining to hominin paleobiology and evolution., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Cercopithecoid monkeys experience relatively high strains along the lingual aspect of the mandibular symphysis because of lateral transverse bending of the mandibular corpora ("wishboning") during mastication. Hylander (Am J Phys Anthropol 64 (1984) 1-46; Am Zool 25 (1985) 315-330) demonstrated that the distribution of strains arising from wishboning loads is comprehensible with reference to the mechanics of curved beams. Theory of curved beams suggests that lingual tensile strains are some multiple of labial compressive strains, yet limitations of experimental methods and uncertainty in estimating parameters needed for theoretical calculations have confounded attempts to characterize the magnitude of this disparity of normal strains. We evaluate the theoretical disparity of normal strains in wishboning in comparison to in vitro strains collected under controlled loads for a sample of mandibles representing two colobine species (N = 6). These data suggest that in colobine monkeys, maximum normal lingual strains should be at least twice maximum labial strains. In addition, we reexamine the distribution of symphyseal stress under an assumption of asymmetric bending, a general approach for calculation of stress appropriate for members that lack a plane of symmetry and are bent along an axis that is not coincident with the member's principal axes. Under asymmetric bending in colobine mandibles, the effect of symphyseal inclination on lingual strain is mitigating at the superior transverse torus and exacerbating at the inferior transverse torus. Relative compliance of colobine mandibular bone further supports the hypothesis that the structural and material properties of the colobine mandibular symphysis do not represent a morphological strategy for minimizing masticatory strain., ((c) 2008 Wiley-Liss, Inc.)

The anterior mandibular corpus of anthropoid primates is routinely subjected to masticatory loads that result in relatively high local levels of stress and strain. While structural morphological responses to these loads have been extensively explored, relatively little is known about material property variation in mandibular bone of nonhuman primates. Consequently, the role of regional and local variation in bone stiffness in conditioning stress and strain gradients is poorly understood. We sampled elastic modulus variation in the bone of the anterior mandibular corpus in two species (N = 3 each) of sympatric colobine monkeys, Procolobus badius and Colobus polykomos. These monkeys were chosen for comparison owing to their distinctive dietary regimens, as P. badius rarely includes hard objects in its diet while C. polykomos habitually processes obdurate items during feeding. Elastic modulus is determined through bone hardness data obtained via microindentation, which enables the description of stiffness variation on sub-millimeter scales. Labial bone stiffness exceeds that of lingual bone in the sample overall. Female mandibular bone is generally stiffer than that found in males, and overall Procolobus mandibular bone is stiffer than that in Colobus. These results, interpreted collectively, suggest that the material response to elevated masticatory stress is increased compliance of the affected bone., ((c) 2008 Wiley-Liss, Inc.)