Dental data challenge the ubiquitous presence of Homo in the Cradle of Humankind.

The origins of Homo, as well as the diversity and biogeographic distribution of early Homo species, remain critical outstanding issues in paleoanthropology. Debates about the recognition of early Homo, first appearance dates, and taxonomic diversity within Homo are particularly important for determining the role that southern African taxa may have played in the origins of the genus. The correct identification of Homo remains also has implications for reconstructing phylogenetic relationships between species of Australopithecus and Paranthropus, and the links between early Homo species and Homo erectus. We use microcomputed tomography and landmark-free deformation-based three-dimensional geometric morphometrics to extract taxonomically informative data from the internal structure of postcanine teeth attributed to Early Pleistocene Homo in the southern African hominin-bearing sites of Sterkfontein, Swartkrans, Drimolen, and Kromdraai B. Our results indicate that, from our sample of 23 specimens, only 4 are unambiguously attributed to Homo, 3 of them coming from Swartkrans member 1 (SK 27, SK 847, and SKX 21204) and 1 from Sterkfontein (Sts 9). Three other specimens from Sterkfontein (StW 80 and 81, SE 1508, and StW 669) approximate the Homo condition in terms of overall enamel-dentine junction shape, but retain Australopithecus-like dental traits, and their generic status remains unclear. The other specimens, including SK 15, present a dominant australopith dental signature. In light of these results, previous dietary and ecological interpretations can be reevaluated, showing that the geochemical signal of one tooth from Kromdraai (KB 5223) and two from Swartkrans (SK 96 and SKX 268) is consistent with that of australopiths.

Prioritizing a high posterior probability threshold leading to low error rate over high classification accuracy: the validity of MorphoPASSE software for cranial morphological sex estimation in a contemporary population.

An increasing number of software tools can be used in forensic anthropology to estimate a biological profile, but further studies in other populations are required for more robust validation. The present study aimed to evaluate the validity of MorphoPASSE software for sex estimation from sexually dimorphic cranial traits recorded on 3D CT models (n = 180) from three populations samples (Czech, French, and Egyptian). Two independent observers performed scoring of 4 cranial traits (2 of them bilateral) in each population sample of 30 males and 30 females. The accuracy of sex estimation using traditional posterior probability threshold (pp = 0.5) ranged from 85.6% to 88.3% and overall classification error from 14.4% to 11.7% for both observers, and corresponds to the previously published values of the method. The MorphoPASSE method is also affected by the subjectivity of the observers, as both observers show agreement in sex assignment in 83.9% of cases, regardless of the accuracy of the estimates. Applying a higher posterior probability threshold (pp 0.95) provided classification accuracy of 97.9% and 93.3% of individuals (for observer A and B respectively), minimizing the risk of error to 2.1% and 6.7%, respectively. However, sex estimation can only be applied to 54% and 66% of individuals, respectively. Our results demonstrate the validity of the MorphoPASSE software for cranial sex estimation outside the reference population. However, the achieved classification success is accompanied by a high risk of errors, the reduction of which is only possible by increasing the posterior probability threshold.

New insights into the variability of upper airway morphology in modern humans.

The biological adaptation of the human lineage to its environment is a recurring question in paleoanthropology. Particularly, how eco-geographic factors (e.g., environmental temperature and humidity) have shaped upper airway morphology in hominins have been subject to continuing debate. Nasal shape is the result of many intertwined factors that include, but are not limited to, genetic drift, sexual selection, or adaptation to climate. A quantification of nasal airway (NA) morphological variation in modern human populations is crucial to better understand these multiple factors. In the present research, we study 195 in vivo CT scans of adult individuals collected in five different geographic areas (Chile, France, Cambodia, Russia, and South Africa). After segmentation of the nasal airway, we reconstruct 3D meshes that are analyzed with a landmark-free geometric morphometrics method based on surface deformation. Our results highlight subtle but statistically significant morphological differences between our five samples. The two morphologically closest groups are France and Russia, whose NAs are longer and narrower, with an important protrusion of the supero-anterior part. The Cambodian sample is the most morphologically distinct and clustered sample, with a mean NA that is wider and shorter. On the contrary, the Chilean sample form the most scattered cluster with the greatest intra-population variation. The South African sample is morphologically close to the Cambodian sample, but also partially overlaps the French and Russian variation. Interestingly, we record no correlation between NA volume and geographic groups, which raises the question of climate-related metabolic demands for oxygen consumption. The other factors of variation (sex and age) have no influence on the NA shape in our samples. However, NA volume varies significantly according both to sex and age: it is higher in males than in females and tends to increase with age. In contrast, we observe no effect of temperature or humidity on NA volume. Finally, we highlight the important influence of asymmetries related to nasal septum deviations in NA shape variation.

Sex assessment using the radius bone in a French sample when applying various statistical models.

Sex estimation of skeletal remains is one of the most important tasks in forensic anthropology. The radius bone is useful to develop standard guidelines for sex estimation across various populations and is an alternative when coxal or femoral bones are not available.The aim of the present study was to assess the sexual dimorphism from radius measurements in a French sample and compare the predictive accuracy of several modelling techniques, using both classical statistical methods and machine learning algorithms.A total of 78 left radii (36 males and 42 females) were used in this study. Sixteen measurements were made. The modelling techniques included a linear discriminant analysis (LDA), flexible discriminant analysis (FDA), regularised discriminant analysis (RDA), penalised logistic regression (PLR), random forests (RF) and support vector machines (SVM).The different statistical models showed an accuracy of classification that is greater than 94%. After selection of variables, the accuracies increased to 97%. The measurements made at the proximal part of the radius (sagittal and transversal diameters of the head, and sagittal diameter of the neck), at distal part (maximum width of the distal epiphysis) and of the entire bone (maximum length) stand out among the various models.The present study suggests that the radius bone constitutes a valid alternative for sex estimation of skeletal remains with comparable classification accuracies to the pelvis or femur and that the non-classical statistical models may provide a novel approach to sex estimation from the radius bone. However, the extrapolation of the current results cannot be made without caution because our sample was composed of very aged individuals.

Sex estimation from long bones: a machine learning approach.

Sex estimation from skeletal remains is one of the crucial issues in forensic anthropology. Long bones can be a valid alternative to skeletal remains for sex estimation when more dimorphic bones are absent or degraded, preventing any estimation from the first intention methods. The purpose of this study was to generate and compare classification models for sex estimation based on combined measurement of long bones using machine learning classifiers. Eighteen measurements from four long bones (radius, humerus, femur, and tibia) were taken from a total of 2141 individuals. Five machine learning methods were employed to predict the sex: a linear discriminant analysis (LDA), penalized logistic regression (PLR), random forest (RF), support vector machine (SVM), and artificial neural network (ANN). The different classification algorithms using all bones generated highly accuracy models with cross-validation, ranging from 90 to 92% on the validation sample. The classification with isolated bones ranked between 83.3 and 90.3% on the validation sample. In both cases, random forest stands out with the highest accuracy and seems to be the best model for our investigation. This study upholds the value of combined long bones for sex estimation and provides models that can be applied with high accuracy to different populations.

Early Neanderthal constructions deep in Bruniquel Cave in southwestern France.

Very little is known about Neanderthal cultures, particularly early ones. Other than lithic implements and exceptional bone tools, very few artefacts have been preserved. While those that do remain include red and black pigments and burial sites, these indications of modernity are extremely sparse and few have been precisely dated, thus greatly limiting our knowledge of these predecessors of modern humans. Here we report the dating of annular constructions made of broken stalagmites found deep in Bruniquel Cave in southwest France. The regular geometry of the stalagmite circles, the arrangement of broken stalagmites and several traces of fire demonstrate the anthropogenic origin of these constructions. Uranium-series dating of stalagmite regrowths on the structures and on burnt bone, combined with the dating of stalagmite tips in the structures, give a reliable and replicated age of 176.5 thousand years (±2.1 thousand years), making these edifices among the oldest known well-dated constructions made by humans. Their presence at 336 metres from the entrance of the cave indicates that humans from this period had already mastered the underground environment, which can be considered a major step in human modernity.

Sex estimation from the greater sciatic notch: a comparison of classical statistical models and machine learning algorithms.

The greater sciatic notch (GSN) is a useful element for sex estimation because it is quite resistant to damage, and thus it can often be assessed even in poorly preserved skeletons. This study aimed to develop statistical models for sex estimation based on visual and metric analyses of the GSN, and additional variables linked to the GSN. A total of 60 left coxal bones (30 males and 30 females) were analysed. Fifteen variables were measured, and one was a morphologic variable. These 16 variables were used for the comparison of six statistical models: linear discriminant analysis (LDA), regularized discriminant analysis (RDA), penalized logistic regression (PLR) and flexible discriminant analysis (FDA), and two machine learning algorithms, support vector machine (SVM) and artificial neural network (ANN). The statistical models were built in two steps: firstly, only with the GSN variables (group 1), and secondly, with the whole variables (group 2), in order to see if the models including all the variables performed better. The overall accuracy of the models was very close, ranging from 0.92 to 0.97 using specific GSN variables. When additional variables starting from the deepest point of GSN are available, it is worth to use them, because the accuracy increases. PLR (after optimization of parameters) stands out from other statistical models. The position of the deepest point of GSN (Fig. 2) probably plays a crucial role for the sexual dimorphism, as stated by the good performance of the visual assessment of this point and the fact that the A2 angle (posterior angle with the deepest point of the GSN as the apex) is included in all models.

Factors associated with SARS-CoV2 infection and care pathways among the most vulnerable populations living in Marseille: a case control study.

BACKGROUND: The Covid-19 pandemic has led to substantial and unexpected increases in morbidity and mortality in France. Vulnerable populations housed in accommodation centres have a greater risk of infection because collective housing and their dependence on social support services mean it is more difficult to apply preventive measures. They are also at greater risk of developing severe forms of Covid-19 and waiting longer before seeking healthcare (for Covid-19 or other) treatment. We aimed to identify the factors associated with SARS-CoV2 infection in the most vulnerable populations in the city of Marseille. METHODS: The study sample comprised users of various services provided by the association AAJT in Marseille, France, some presenting symptoms suggestive of Covid-19 and others not. All had routine health surveillance provided by AAJT's dedicated healthcare team between March 2020 and May 2020. Using univariate and multivariate analyses, we studied the influence of several variables on morbidity associated with Covid-19. RESULTS: The study included 64 participants, 29 of whom tested positive for Covid-19 and 35 control subjects. Median age was 21.16 years old. Individuals in the 'Covid-19 case' group (p < 0.005) - which included persons testing positive and those suspected of being infected - were younger. The study sample's male/female ratio was seven. In our multivariate analyses, living in a shared apartment and poor adherence to social distancing measures were factors associated with Covid-19 infection. Furthermore, mental health problems - such as anxiety disorder - were very frequent in the study sample. CONCLUSIONS: Allocating more and specific housing units to structures providing accommodation services to the most vulnerable people would seem to be a decisive factor in controlling the spread of SARS-CoV2, and deserves more attention from public authorities.

Diaphysator: An online application for the exhaustive cartography and user-friendly statistical analysis of long bone diaphyses.

The cross-sectional geometry (CSG) of long bone diaphyses is used in bioanthropology to evaluate their resistance to biomechanical constraints and to infer life-history-related patterns such as mobility, activity specialization or intensity, sexual dimorphism, body mass and proportions. First limited by technical analytical constraints to the analysis of one or two cross sections per bone, it has evolved into the analysis of cross sections of the full length of the diaphyseal part of long bones. More recently, researchers have developed analytical tools to map the cortical thickness of entire diaphyses to evaluate locomotor signatures. However, none of these analytical tools are easy to use for scientists who are not familiar with computer programming, and some statistical procedures-such as mapping the correlation coefficients of the diaphyseal thickness with various parameters have yet to be made available. Therefore, we developed an automated and open-source application that renders those analyses (both CSG and cortical thickness) in a semiautomated and user friendly manner. This application, called "Diaphysator", is associated with another free software ("Extractor", presented in Dupej et al. (2017). American Journal of Physical Anthropology, 164, 868-876). Diaphysator can be used as an online application (https://diaphysator.shinyapps.io/maps) or as a package for R statistical software. Along with the mean maps of cortical thickness and mean CSG parameter graphs, the users can evaluate the correlations and partial correlations of both CSG parameters at every cross section along the diaphyseal length, and cortical thickness data points of the entire diaphysis, with any factor such as age, sex, stature, and body mass.

A method of sexing the human os coxae based on logistic regressions and Bruzek's nonmetric traits.

OBJECTIVES: This study aims at proposing a visual method for sexing the human os coxae based on a statistical approach, using a scoring system of traits described by Bruzek (2002). This method is evaluated on a meta-population sample, where the data were acquired by direct observation of dry bones as well as computed tomography (CT) scans. A comparison with the original Bruzek's (2002) method is performed. MATERIALS AND METHODS: Five hundred and ninety two ossa coxae of modern humans are included in the reference dataset. Two other samples, composed respectively of 518 ossa coxae and 99 CT-scan images, are both used for validation purposes. The individuals come from five European or North American population samples. Eleven trichotomic traits (expressing female, male, or intermediate forms) were observed on each os coxae. The new approach employs statistical processing based on logistic regressions. An R package freely available online, PELVIS, implements both methods. RESULTS: Both methods provide highly reliable sex estimates. The new statistical method has a slightly better accuracy rate (99.2%) than the former method (98.2%) but has also a higher rate of indeterminate individuals (12.9% vs. 3% for complete bones). CONCLUSION: The efficiency of both methods is compared. Low error rates were preferred over high ability of reaching the classification threshold. The impact of lateralization and the asymmetry of observed traits are discussed. Finally, it is shown that this visual method of sex estimation is reliable and easy to use through the graphical user interface of the R package.

AnthropMMD: An R package with a graphical user interface for the mean measure of divergence.

The mean measure of divergence is a dissimilarity measure between groups of individuals described by dichotomous variables. It is well suited to datasets with many missing values, and it is generally used to compute distance matrices and represent phenograms. Although often used in biological anthropology and archaeozoology, this method suffers from a lack of implementation in common statistical software. A package for the R statistical software, AnthropMMD, is presented here. Offering a dynamic graphical user interface, it is the first one dedicated to Smith's mean measure of divergence. The package also provides facilities for graphical representations and the crucial step of trait selection, so that the entire analysis can be performed through the graphical user interface. Its use is demonstrated using an artificial dataset, and the impact of trait selection is discussed. Finally, AnthropMMD is compared to three other free tools available for calculating the mean measure of divergence, and is proven to be consistent with them.

Architecture of the femoral and tibial diaphyses in relation to body mass and composition: Research from whole-body CT scans of adult humans.

OBJECTIVES: Recent investigations have evaluated the influence of body composition on long bones in order to overcome the limits of body mass (BM) estimation methods and eventually lead to studying nutrition in past populations. Knowing how fat mass (FM) and fat-free mass (FFM) impact the skeleton would also enhance the understanding of mobility, activity, and locomotion derived from bone architecture. We investigated the relationship between BM and composition, and the architecture of the entire tibial and femoral diaphyses in an adult sample representative of a wide range of variation in age, BM, and composition. MATERIALS AND METHODS: Body composition was measured directly from 78 whole-body CT scans for which the age, sex, BM, and stature were recorded. The entire diaphyseal thickness, volume, curvature, and cross-sectional geometry parameters of both the femur and tibia were numerically extracted. RESULTS: FM correlates with large portions of the femoral thickness in females only. FFM correlates with the femoral diaphysis in males but not in females. FFM correlates with the tibia architecture in both sexes, while FM is correlated in males exclusively. DISCUSSION: BM and body components influence the architecture of the diaphysis of lower limb long bones in sex-specific patterns that are mostly reflected in their thickness and can be recorded, in some cases, for their strength, rigidity, and volume. Our results suggest that (1) long bone diaphyses should be thoroughly studied, as a whole, when possible; and (2) BM and body components should be accounted for when deriving activity, mobility, or locomotion patterns from cortical bone.

Sex-specific functional adaptation of the femoral diaphysis to body composition.

OBJECTIVES: The human femoral diaphysis is often used to reconstruct loading histories (mobility, activity, body mass). The proximal femur is known to be differentially affected by changes in total fat-mass (FM), fat-free mass (FFM), and body fat percentage (BF%), but the adaptation of the entire diaphysis to body composition has not been thoroughly characterized to date. Understanding how the femoral diaphysis adapts to body components would benefit biomechanical interpretations of the femoral variation and nutrition-related studies. METHODS: Combining various methods from clinical nutrition, biological anthropology, and geometric morphometrics, we evaluated the correlation of measures taken on the entire femoral diaphysis with estimated FM, FFM, and BF% from 61 CT scans (17 females, 44 males). The sample was predominantly composed of people with obesity. RESULTS: Cortical area of the cross-sections and local cortical thickness showed high correlation with BF% in particular, in females only. The curvature significantly decreased with FM and BF% in both sexes. The lowest correlations are found with FFM. CONCLUSIONS: The observed sexual dimorphism is consistent with differing aging processes; cortical bone decreases in females through endosteal resorption while it remains almost constant in males who compensate for endosteal resorption by periosteal apposition on the diaphyseal surface. The functional adaptation to compressive forces indicates a systemic endosteal apposition of bone material with increased BF% and FM in females only. FM and BF% are linked to a straighter femur in both sexes, suggesting an optimization of the resistance to compressive loads by distributing them more linearly along the entire diaphysis.

Validation and reliability of the sex estimation of the human os coxae using freely available DSP2 software for bioarchaeology and forensic anthropology.

OBJECTIVES: A new tool for skeletal sex estimation based on measurements of the human os coxae is presented using skeletons from a metapopulation of identified adult individuals from twelve independent population samples. For reliable sex estimation, a posterior probability greater than 0.95 was considered to be the classification threshold: below this value, estimates are considered indeterminate. By providing free software, we aim to develop an even more disseminated method for sex estimation. MATERIALS AND METHODS: Ten metric variables collected from 2,040 ossa coxa of adult subjects of known sex were recorded between 1986 and 2002 (reference sample). To test both the validity and reliability, a target sample consisting of two series of adult ossa coxa of known sex (n = 623) was used. The DSP2 software (Diagnose Sexuelle Probabiliste v2) is based on Linear Discriminant Analysis, and the posterior probabilities are calculated using an R script. RESULTS: For the reference sample, any combination of four dimensions provides a correct sex estimate in at least 99% of cases. The percentage of individuals for whom sex can be estimated depends on the number of dimensions; for all ten variables it is higher than 90%. Those results are confirmed in the target sample. DISCUSSION: Our posterior probability threshold of 0.95 for sex estimate corresponds to the traditional sectioning point used in osteological studies. DSP2 software is replacing the former version that should not be used anymore. DSP2 is a robust and reliable technique for sexing adult os coxae, and is also user friendly.

Detecting menarcheal status through dental mineralization stages?

Menarche is an indicator frequently used to study variation in growth, development, and related health conditions among members of living populations. As a life event, menarche is often associated with changes in an individual's social identity. The reproductive lifespan, which for females starts with menarche, is a paramount feature of palaeodemographic studies. Determination of menarche status from the skeletal remains of individuals of past populations can be obtained by assessing the developmental status of the iliac crest, as well as the hand and wrist bones, which are, unlike teeth, often poorly recovered in bioarchaeological contexts. The present study seeks to evaluate the link between dental mineralization and menarche in a population of known menarche status. The relationship between permanent teeth mineralization and menarche status was investigated by using data of developing permanent teeth (167 radiographs) rated in accordance with the well-known standards of Demirjian et al. and Moorrees et al. collected among 73 living French females of known menarcheal status. Using correlation ratios, GLMM and CART algorithm, menarcheal status is correlated with mineralization of the premolars. Menarcheal status is predicted correctly for 92 and 77% of radiographs of the learning and validation samples, respectively. Although promising, the results require caution prior to generalization to other populations. The age of menarche in this particular sample may simply coincide with the development of the premolars in this particular sample. Therefore, further investigation applied to populations with various mean ages of menarche is required in order to provide new evidence of variation in human growth and development from the correspondence between the mineralization of the permanent teeth and menarche.

In situ study of the Gravettian individual from Cussac cave, locus 2 (Dordogne, France).

OBJECTIVES: Cussac cave, discovered in 2000, is characterized by the exceptional presence of monumental engravings and human remains deposited in bear nests. Both the style of the art and a direct radiocarbon date indicate a Gravettian age. As the cave is protected as a national heritage site, only very limited access to and restricted direct interventions involving the human remains are possible. Here, we present the results of observations and measurements of Cussac L2A, represented by a virtually complete skeleton covered with a layer of clay. MATERIALS AND METHODS: A portion of the clay that covered some bones was removed in order to undertake a study of the skeleton in situ. The age-at-death was assessed using several indicators, especially changes on the auricular surface of the ilium. The sex was assessed using the morphology and morphometrics of the coxal bones. Cussac L2A stature, humero-femoral index, and crural index were also estimated. The dimensions of the Cussac L2A skeletal remains are compared with the other European Gravettian and Late Upper Paleolithic human remains using adjusted Z-Scores. RESULTS: The analysis indicates that Cussac L2A is probably a male who died aged between 20 and 50 years. If the sex assessment is correct, with an averaged estimated stature of 1.64 m, Cussac L2A would be one of the shorter Gravettian males. DISCUSSION: These results raise the importance of the new discoveries to better understand the variability of Upper Paleolithic skeletal morphology and stress the difficulties in marrying heritage preservation and scientific investigations.

Unraveling the Life History of Past Populations through Hypercementosis: Insights into Cementum Apposition Patterns and Possible Etiologies Using Micro-CT and Confocal Microscopy.

The "teeth-as-tools" hypothesis posits that Neanderthals used their anterior teeth as a tool or a third hand for non-dietary purposes. These non- or para-masticatory activities (e.g., tool-making or food preparation prior to ingestion) have also been described in other past and extant human populations, and other Primates. Cementum is the mineralized tissue that covers the tooth root surface and anchors it to the alveolar bone. Under certain conditions (e.g., mechanical stress, infection), its production becomes excessive (i.e., beyond the physiological state) and is called 'hypercementosis'. Several studies in dental anthropology have established a correlation between the teeth-as-tools and hypercementosis. The present work aims to characterize the different patterns of cementum apposition on archeological teeth and discuss their supposed etiology. Using microtomography and confocal microscopy, the patterns of cementum apposition (i.e., thickness, location, and surface characteristics) were analyzed in 35 hypercementotic teeth (Sains-en-Gohelle, France; 7th-17th c. A.D.). Four groups were identified with distinct hypercementosis patterns: (1) impacted, (2) infected, (3) hypofunctional, and (4) hyperfunctional teeth. Characterizing hypercementosis can contribute to documenting the oral health status (paleopathology) and/or masticatory activity of individuals, even from isolated teeth. This has implications for the study of fossil hominins, particularly Neanderthals, known for their use of anterior teeth as tools and frequent and substantial occurrence of hypercementosis.

Life history of the individuals buried in the St. Benedict Cemetery (Prague, 15th-18th centuries): insights from (14)C dating and stable isotope (δ(13)C, δ(15)N, δ(18)O) analysis.

Funerary practices and bioarchaeological (sex and age) data suggest that a mortality crisis linked to an epidemic episode occurred during the fifth phase of the St. Benedict cemetery in Prague (Czech Republic). To identify this mass mortality episode, we reconstructed individual life histories (dietary and mobility factors), assessed the population's biological homogeneity, and proposed a new chronology through stable isotope analysis (δ(13)C, δ(18)O and δ(15)N) and direct radiocarbon dating. Stable isotope analysis was conducted on the bone and tooth enamel (collagen and carbonate) of 19 individuals from three multiple graves (MG) and 12 individuals from individual graves (IG). The δ(15)N values of collagen and the difference between the δ(13)C values of collagen and bone carbonate could indicate that the IG individuals had a richer protein diet than the MG individuals or different food resources. The human bone and enamel carbonate and δ(18)O values suggest that the majority of individuals from MG and all individuals from IG spent most of their lives outside of the Bohemian region. Variations in δ(18)O values also indicate that all individuals experienced residential mobility during their lives. The stable isotope results, biological (age and sex) data and eight (14)C dates clearly differentiate the MG and IG groups. The present work provides evidence for the reuse of the St. Benedict cemetery to bury soldiers despite the funeral protest ban (1635 AD). The Siege of Prague (1742 AD) by French-Bavarian-Saxon armies is identified as the cause of the St. Benedict mass mortality event.

Exploring the relative influence of raw materials, percussion techniques, and hominin skill levels on the diversity of the early Oldowan assemblages: Insights from the Shungura Formation, Lower Omo Valley, Ethiopia.

The eastern African Oldowan has been documented in multiple raw material contexts and physical environments and displays considerable differences in terms of technological complexity. The relative influence of percussion techniques and raw material quality are central to debates concerning hominin skill levels as a potential driver of change during the period between 2.6 and 2 million-years (Ma). The early Oldowan assemblages from the Shugura Formation play a key role in these debates due to a number of distinctive features, including the small size of the artefacts and poorly controlled flaking. Here we mobilize quantified and replicable experimental data in order to (a) assess the significance of the bipolar technique in the Omo archaeological assemblages and (b) discriminate the respective impact of raw materials, technical choices and knapper skill levels on the unique character of these assemblages. By combining descriptive statistics with regression tree models, our analysis demonstrates knapper skill level to be of minimal importance in this context for the production of sharp-edged flakes. The absence of a link between skill and knapping success reflects the combined effect of raw material constraints, the frequent use of the bipolar technique, and relatively simple technical objectives. Our analysis confirms the key role played by local environmental conditions in the unique appearance of the Shungura assemblages, a relationship which has been frequently suggested but never demonstrated. Beyond the operational and sensorimotor skills considered in most studies, we suggest that the diversity of early Oldowan assemblages should be better sought in the cognitive abilities developed by early toolmakers as a response to landscape learning and use, two elements of early human evolution that remain largely unexplored.

The Distribution and Biogenic Origins of Zinc in the Mineralised Tooth Tissues of Modern and Fossil Hominoids: Implications for Life History, Diet and Taphonomy.

Zinc is incorporated into enamel, dentine and cementum during tooth growth. This work aimed to distinguish between the processes underlying Zn incorporation and Zn distribution. These include different mineralisation processes, the physiological events around birth, Zn ingestion with diet, exposure to the oral environment during life and diagenetic changes to fossil teeth post-mortem. Synchrotron X-ray Fluorescence (SXRF) was used to map zinc distribution across longitudinal polished ground sections of both deciduous and permanent modern human, great ape and fossil hominoid teeth. Higher resolution fluorescence intensity maps were used to image Zn in surface enamel, secondary dentine and cementum, and at the neonatal line (NNL) and enamel-dentine-junction (EDJ) in deciduous teeth. Secondary dentine was consistently Zn-rich, but the highest concentrations of Zn (range 197-1743 ppm) were found in cuspal, mid-lateral and cervical surface enamel and were similar in unerupted teeth never exposed to the oral environment. Zinc was identified at the NNL and EDJ in both modern and fossil deciduous teeth. In fossil specimens, diagenetic changes were identified in various trace element distributions but only demineralisation appeared to markedly alter Zn distribution. Zinc appears to be tenacious and stable in fossil tooth tissues, especially in enamel, over millions of years.