Morphological integration affects the evolution of midline cranial base, lateral basicranium, and face across primates

Objectives The basicranium and face are two integrated bony structures displaying great morphological diversity across primates. Previous studies in hominids determined that the basicranium is composed of two independent modules: the midline basicranium, mostly influenced by brain size, and the lateral basicranium, predominantly associated with facial shape. To better assess how morphological integration impacts the evolution of primate cranial shape diversity, we test to determine whether the relationships found in hominids are retained across the order. Materials and methods Three-dimensional landmarks (29) were placed on 143 computed tomography scans of six major clades of extant primate crania. We assessed the covariation between midline basicranium, lateral basicranium, face, and endocranial volume using phylogenetically informed partial least squares analyses and phylogenetic generalized least squares models. Results We found significant integration between lateral basicranium and face and between midline basicranium and face. We also described a significant correlation between midline basicranium and endocranial volume but not between lateral basicranium and endocranial volume. Discussion Our findings demonstrate a significant and pervasive integration in the craniofacial structures across primates, differing from previous results in hominids. The uniqueness of module organization in hominids may explain this distinction. We found that endocranial volume is significantly integrated to the midline basicranium but not to the lateral basicranium. This finding underlines the significant effect of brain size on the shape of the midline structures of the cranial base in primates. With the covariations linking the studied features defined here, we suggest that future studies should focus on determining the causal links between them

Basicranium and face: Assessing the impact of morphological integration on primate evolution

The basicranium and facial skeleton are two integrated structures displaying great morphological diversity across primates. Previous studies focusing on limited taxonomic samples have demonstrated that morphological integration has a significant impact on the evolution of these structures. However, this influence is still poorly understood. A more complete understanding of craniofacial integration across primates has important implications for functional hypotheses of primate evolution. In the present study, we analyzed a large sample of primate species to assess how integration affects the relationship between basicranial and facial evolutionary pathways across the order. First, we quantified integration and modularity between basicranium and face using phylogenetically-informed partial least squares analyses. Then, we defined the influence of morphological integration between these structures on rates of evolution, using a time-calibrated phylogenetic tree, and on disparity through time, comparing the morphological disparity across the tree with that expected under a pure Brownian process. Finally, we assessed the correlation between the basicranium and face, and three factors purported to have an important role in shaping these structures during evolution: endocranial volume, positional behavior (i.e., locomotion and posture), and diet. Our findings show that the face and basicranium, despite being highly integrated, display significantly different evolutionary rates. However, our results demonstrate that morphological integration impacted shape disparity through time. We also found that endocranial volume and positional behavior are important drivers of cranial shape evolution, partly affected by morphological integration. (C) 2018 Elsevier Ltd. All rights reserved

Relationship between foramen magnum position and locomotion in extant and extinct hominoids

From the Miocene Sahelanthropus tchadensis to Pleistocene Homo sapiens, hominins are characterized by a derived anterior position of the foramen magnum relative to basicranial structures. It has been previously suggested that the anterior position of the foramen magnum in hominins is related to bipedal locomotor behavior. Yet, the functional relationship between foramen magnum position and bipedal locomotion remains unclear. Recent studies, using ratios based on cranial linear measurements, have found a link between the anterior position of the foramen magnum and bipedalism in several mammalian clades: marsupials, rodents, and primates. In the present study, we compute these ratios in a sample including a more comprehensive data set of extant hominoids and fossil hominins. First, we verify if the values of ratios can distinguish extant humans from apes. Then, we test whether extinct hominins can be distinguished from non-bipedal extant hominoids. Finally, we assess if the studied ratios are effective predictors of bipedal behavior by testing if they mainly relate to variation in foramen magnum position rather than changes in other cranial structures. Our results confirm that the ratios discriminate between extant bipeds and non-bipeds. However, the only ratio clearly discriminating between fossil hominins and other extant apes is that which only includes basicranial structures. We show that a large proportion of the inter-specific variation in the other ratios relates to changes in facial, rather than basicranial, structures. In this context, we advocate the use of measurements based only on basicranial structures when assessing the relationship between foramen magnum position and bipedalism in future studies. (C) 2017 Elsevier Ltd. All rights reserved

4500 years of morphological diversification in Western Europe wild boars (Sus scrofa) and the consequences of the Neolithic transition

International audienceEvolutionary biologists have recently solicited archaeologists to help document and understand the morphological evolution of animals in response to human activities and, more generally, to help reconstruct the history and significance of the anthropogenic impact on worldwide ecosystems. Artificial selection associated with domestication is the best-known example of a major anthropogenic morphological evolution preserved in the archaeological record. However, the impact of the domestication process and dispersal on the morphological evolution of animals has been far less explored. To fill this gap, we focused on 4500 years of evolution in Western Europe Sus scrofa, covering the Neolithic transition ‒ a major anthropogenic ecological disturbance involving landscape modification and the translocation of domestic mammals. Using geometric morphometrics on key phenotypic markers preserved in the archaeological record, associated with isotopic studies, we explored how, and in response to which cultural drivers, the Neolithic niche construction has influenced the morphological evolution of Western European wild boars (Sus scrofa scrofa). The decoupling of size and shape components from bone morphological variation has facilitated the identification of several processes of phenotypic diversification of Sus s. scrofa in response to human behaviour during the Neolithic transition in Western Europe