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The process of animal domestication is a key evolutionary transition in human history, within which the control of wild populations is considered a crucial first step. Yet, phenotypic changes associated with animal captivity remain challenging to document. Here, we investigated the craniofacial changes in wild boar ( Sus scrofa ) associated with a lifetime of growth in captivity under conditions of controlled mobility and diet. Using three-dimensional landmark-based geometric morphometrics, we assessed cranial and mandibular size and shape differences between captive and wild-caught wild boar, their link with masticatory forces, and how these plastic changes relate to traits selected in domestic pigs. We observed shape divergence associated with greater masticatory forces in captive wild boar (e.g., wider zygomatic arches, more upright mandibular rami, and reduced gonial angle) corroborating the fundamental role of biomechanical loading and constructional constraints in the skull shape changes associated with captivity. Despite their resemblance with domestic traits, these localised plastic changes follow a different phenotypic trajectory, suggesting that they did not contribute to the setup of the craniofacial morphology of current domestic breeds. A parallel increase of masticatory force in captive wild boars and domestic pigs may explain this phenotypic convergence but needs to be further explored.

We analyzed feeding biomechanics in pitheciine monkeys (Pithecia, Chiropotes, Cacajao), a clade that specializes on hard-husked unripe fruit (sclerocarpy) and resistant seeds (seed predation). We tested the hypothesis that pitheciine crania are well-suited to generate and withstand forceful canine and molar biting, with the prediction that they generate bite forces more efficiently and better resist masticatory strains than the closely-related Callicebus, which does not specialize on unripe fruits and/or seeds. We also tested the hypothesis that Callicebus-Pithecia-Chiropotes-Cacajao represent a morphocline of increasing sclerocarpic specialization with respect to biting leverage and craniofacial strength, consistent with anterior dental morphology. We found that pitheciines have higher biting leverage than Callicebus and are generally more resistant to masticatory strain. However, Cacajao was found to experience high strain magnitudes in some facial regions. We therefore found limited support for the morphocline hypothesis, at least with respect to the mechanical performance metrics examined here. Biting leverage in Cacajao was nearly identical (or slightly less than) in Chiropotes and strain magnitudes during canine biting were more likely to follow a Cacajao-Chiropotes-Pithecia trend of increasing strength, in contrast to the proposed morphocline. These results could indicate that bite force efficiency and derived anterior teeth were selected for in pitheciines at the expense of increased strain magnitudes. However, our results for Cacajao potentially reflect reduced feeding competition offered by allopatry with other pitheciines, which allows Cacajao species to choose from a wider variety of fruits at various stages of ripeness, leading to reduction in the selection for robust facial features. We also found that feeding biomechanics in sympatric Pithecia and Chiropotes are consistent with data on food structural properties and observations of dietary niche separation, with the former being well-suited for the regular molar crushing of hard seeds and the latter better adapted for breaching hard fruits.

The divergence of Homo from gracile australopiths has been described as a trend of decreasing dentognathic size and robusticity, precipitated by stone tool use and/or a shift to softer foods, including meat. Yet, mechanical evidence supporting this narrative is sparse, and isotopic and archaeological data have led to the suggestion that a shift away from a gracile australopith-like diet would not have occurred in the most basal members of Homo but rather only with the appearance of Homo erectus, implying that the origin of our genus is not rooted in dietary change. Here, we provide mechanical evidence that Homo habilis exhibits an australopith-like pattern of facial strain during biting but, unlike most australopiths, was not suited for a diet that required forceful processing by the molar teeth. Homo habilis was at elevated risk of distractive jaw joint forces during those bites, constraining muscle recruitment so as to avoid generating uncomfortable/dangerous levels of tension in the joint. Modern humans have similar limitations. This suggests that selection on skeletal traits favouring forceful postcanine processing was relaxed by the earliest stages in the evolution of our genus, implying that dietary or food processing changes played an important role in the emergence of Homo .

The organization of the bony face is complex, its morphology being influenced in part by the rest of the cranium. Characterizing the facial morphological variation and craniofacial covariation patterns in extant hominids is fundamental to the understanding of their evolutionary history. Numerous studies on hominid facial shape have proposed hypotheses concerning the relationship between the anterior facial shape, facial block orientation and basicranial flexion. In this study we test these hypotheses in a sample of adult specimens belonging to three extant hominid genera (Homo, Pan and Gorilla). Intraspecific variation and covariation patterns are analyzed using geometric morphometric methods and multivariate statistics, such as partial least squared on three-dimensional landmarks coordinates. Our results indicate significant intraspecific covariation between facial shape, facial block orientation and basicranial flexion. Hominids share similar characteristics in the relationship between anterior facial shape and facial block orientation. Modern humans exhibit a specific pattern in the covariation between anterior facial shape and basicranial flexion. This peculiar feature underscores the role of modern humans' highly-flexed basicranium in the overall integration of the cranium. Furthermore, our results are consistent with the hypothesis of a relationship between the reduction of the value of the cranial base angle and a downward rotation of the facial block in modern humans, and to a lesser extent in chimpanzees.

Dental microwear has been widely used to reconstruct mammals’ past diet and to understand their dental evolution. In archaeology, it can help reconstruct anthropogenic herd-feeding systems. However, deciphering the impact of exogenous mineral particles on dental wear is an ongoing challenge since studies have shown that soil ingestion can generates microwear traces that interfere with the dietary signals. To bridge this gap, this study relies on the first large-scale controlled-food experiment on wild boars (Sus scrofa) to test how soil ingestion can affect the dietary signal recorded in dental microwear. It provides the opportunity to investigate the impact of natural soil ingestion over microwear traces by comparing penned boars that were able to root with stalled boars that were not. We performed 3D Dental microwear texture analysis (DMTA) on 22 controlled-fed boars kept captive either in an indoor stall with no soil ingestion, or in a wooded pen with natural soil ingestion. We analysed shearing and crushing facets on upper and lower first and second molars using standard texture parameters. We also conducted particle size distribution analyses of the ingested soil. In line with previous works, the consumption of exogenous abrasives in rooting boars leads to less rough, less complex and more anisotropic wear surfaces than in stall-fed boars, even though they received the same diet. Thus, we highly recommend studying DMT when investigating ancient pig husbandry systems, particularly local changes in food management. Overall, this study contributes to a better comprehension of how exogenous abrasives impact DMT among mammals.

The basicranium and face have been linked through genetic, developmental, and functional relationships throughout their evolution. As a result, basicranial morphology most likely plays a major role in the evolution of facial structures. We describe the relationships between basicranial flexion and the face in Homo , Pan , and Gorilla to determine the role of cranial base angle reduction in the setup of the short and orthognathic face of Homo . We test the hypotheses that cranial base flexion plays a significant part in variation in facial orientation, length, and projection at the intraspecific level. The sample comprised 125 crania of adult specimens including 66 Homo sapiens , 32 Pan troglodytes , and 27 Gorilla gorilla . We described the cranial base and face using landmarks placed on scans of the surfaces and computed correlations between the cranial base angle and facial orientation, length, and projection. Our results support the hypotheses that cranial base flexion plays a significant part in facial orientation for Homo and Pan and in facial length for Pan . The hypothesis that basicranial flexion is related to a reduction of facial projection is not supported. The findings suggest that basicranial flexion can explain several anatomical specificities of hominins, including the reduction of prognathism and the reduction of the length of the nasopharynx. We found different patterns in the different genera, highlighting the fact that changes in the relationship between craniofacial structures may have occurred during hominid evolution.

The process of animal domestication is a key evolutionary transition in human history, within which the control of wild populations is considered a crucial first step. Yet, phenotypic changes associated with animal captivity remain challenging to document. Here, we investigated the craniofacial changes in wild boar (Sus scrofa) associated with a lifetime of growth in captivity under conditions of controlled mobility and diet. Using three-dimensional landmark-based geometric morphometrics, we assessed cranial and mandibular size and shape differences between captive and wild-caught wild boar, their link with masticatory forces, and how these plastic changes relate to traits selected in domestic pigs. We observed shape divergence associated with greater masticatory forces in captive wild boar (e.g., wider zygomatic arches, more upright mandibular rami, and reduced gonial angle) corroborating the fundamental role of biomechanical loading and constructional constraints in the skull shape changes associated with captivity. Despite their resemblance with domestic traits, these localised plastic changes follow a different phenotypic trajectory, suggesting that they did not contribute to the setup of the craniofacial morphology of current domestic breeds. A parallel increase of masticatory force in captive wild boars and domestic pigs may explain this phenotypic convergence but needs to be further explored.

The face is a complex organization of bones, the morphology of which is partly influenced by the rest of the cranium (e.g., the cranial base and the neurocranium). The characterization of facial morphological variation and craniofacial covariation patterns in extant hominids is fundamental for the understanding of their evolutionary history. While facial orientation on facial shape is important, as has been suggested, few studies have considered this character. In this study, the aim is to assess the morphological relationship between facial shape and facial orientation. The morphological covariation between facial shape and facial orientation is assessed. To achieve this aim, geometric morphometrics (landmark positioning, and Procrustes superimposition) and multivariate statistics (partial least squares) are used on 3-D virtual crania of three extant hominid genera (Homo, Pan, and Gorilla). Results show a significant covariation between facial shape and facial orientation. Facial orientation and basicranial flexion are strongly related to facial shape characters such as facial enlargement, lower face reduction, nasal aperture shape, and orbit shape. This study raises important new elements of major interest in the discussion of the relationship between facial shape and facial and basicranial orientation in the development of modern human facial characteristics during evolution. This study also highlights the great variety in facial morphology present in extant hominids and their species-specific pattern of facial shape relative to facial positioning. This work notably underscores the peculiar facial shape pattern in Homo as linked to its important basicranial flexion and its short and orthognatic face.