Distinct growth of the nasomaxillary complex in Au. sediba

Occipital bone modeling patterns during the first years of life: A preliminary histological and quantitative approach

Studies of modeling processes have provided important insights in human evolutionary discipline. Most of these studies are based on facial bones and in much lesser extent on other bones such as those from the cranial vault. Thus, this study fills a gap in research by examining occipital bone modeling in subadults, adding individuals under 2 years old and expanding the sample size available to date. The sample comprise 14 subadults occipitals (4 months to 5 years) from archeological sites spanning the thirteenth to the eighteenth century. Resin replicas coated with gold were elaborated to examine the modeling patterns using scanning electron microscopy and the results of this analysis are illustrated in the modeling maps. The percentages of deposition and resorption were calculated to enable the comparison of the modeling patterns between individuals. The analysis unveiled a pattern of resorption predominance in younger individuals, shifting to deposition around 3 years old before reverting to resorption in older individuals. Symmetry in modeling processes between left and right halves of the occipital was observed, suggesting stability in bone modeling. Comparisons with previous studies showed variations in modeling patterns influenced by factors like age. Overall, this study sheds light on occipital bone modeling processes, highlighting the importance of sample size and quantitative analysis in the interpretation of modeling maps. Further research is justified to comprehensively explore occipital modeling patterns, particularly during the early stages of development.

A shared pattern of midfacial bone modelling in hominids suggests deep evolutionary roots for human facial morphogenesis

Midfacial morphology varies between hominoids, in particular between great apes and humans for which the face is small and retracted. The underlying developmental processes for these morphological differences are still largely unknown. Here, we investigate the cellular mechanism of maxillary development (bone modelling, BM), and how potential changes in this process may have shaped facial evolution. We analysed cross-sectional developmental series of gibbons, orangutans, gorillas, chimpanzees and present-day humans (n = 183). Individuals were organized into five age groups according to their dental development. To visualize each species's BM pattern and corresponding morphology during ontogeny, maps based on microscopic data were mapped onto species-specific age group average shapes obtained using geometric morphometrics. The amount of bone resorption was quantified and compared between species. Great apes share a highly similar BM pattern, whereas gibbons have a distinctive resorption pattern. This suggests a change in cellular activity on the hominid branch. Humans possess most of the great ape pattern, but bone resorption is high in the canine area from birth on, suggesting a key role of canine reduction in facial evolution. We also observed that humans have high levels of bone resorption during childhood, a feature not shared with other apes.

The various meanings and uses of bone "remodeling" in biological anthropology: A review

OBJECTIVES

In modern bone biology, the term "remodeling" generally refers to internal bone turnover that creates secondary osteons. However, it is also widely used by skeletal biologists, including biological anthropologists as a catch-all term to refer to different skeletal changes. In this review, we investigated how "remodeling" is used across topics on skeletal biology in biological anthropology to demonstrate potential problems with such pervasive use of a generalized term.

METHODS

Using PubMed and Google Scholar, we selected and reviewed 205 articles that use the term remodeling to describe skeletal processes and have anthropological implications. Nine edited volumes were also reviewed as examples of collaborative work by different experts to demonstrate the diverse and extensive use of the term remodeling.

RESULTS

Four general meanings of bone "remodeling" were identified, namely, internal turnover, functional adaptation, fracture repair, and growth remodeling. Additionally, remodeling is also used to refer to a broad array of pathological skeletal changes.

DISCUSSION

Although we initially identified four general meanings of bone remodeling, they are not mutually exclusive and often occur in combination. The term "remodeling" has become an extensively used catch-all term to refer to different processes and outcomes of skeletal changes, which inevitably lead to misunderstanding and a loss of information. Such ambiguity and confusion are potentially problematic as the field of biological anthropology becomes increasingly multidisciplinary. Therefore, we advocate for precise, context-specific definitions and explanations of bone remodeling as it continues to be used across disciplines within and beyond biological anthropology.

Reappraising the palaeobiology of Australopithecus

The naming of Australopithecus africanus in 1925, based on the Taung Child, heralded a new era in human evolutionary studies and turned the attention of the then Eurasian-centric palaeoanthropologists to Africa, albeit with reluctance. Almost one hundred years later, Africa is recognized as the cradle of humanity, where the entire evolutionary history of our lineage prior to two million years ago took place-after the Homo-Pan split. This Review examines data from diverse sources and offers a revised depiction of the genus and characterizes its role in human evolution. For a long time, our knowledge of Australopithecus came from both A. africanus and Australopithecus afarensis, and the members of this genus were portrayed as bipedal creatures that did not use stone tools, with a largely chimpanzee-like cranium, a prognathic face and a brain slightly larger than that of chimpanzees. Subsequent field and laboratory discoveries, however, have altered this portrayal, showing that Australopithecus species were habitual bipeds but also practised arboreality; that they occasionally used stone tools to supplement their diet with animal resources; and that their infants probably depended on adults to a greater extent than what is seen in apes. The genus gave rise to several taxa, including Homo, but its direct ancestor remains elusive. In sum, Australopithecus had a pivotal bridging role in our evolutionary history owing to its morphological, behavioural and temporal placement between the earliest archaic putative hominins and later hominins-including the genus Homo.

Population affinity and variation of sexual dimorphism in three-dimensional facial forms: comparisons between Turkish and Japanese populations

Examining the extent to which sex differences in three-dimensional (3D) facial soft tissue configurations are similar across diverse populations could suggest the source of the indirect evolutionary benefits of facial sexual dimorphism traits. To explore this idea, we selected two geographically distinct populations. Three-dimensional model faces were derived from 272 Turkish and Japanese men and women; their facial morphologies were evaluated using landmark and surface-based analyses. We found four common facial features related to sexual dimorphism. Both Turkish and Japanese females had a shorter lower face height, a flatter forehead, greater sagittal cheek protrusion in the infraorbital region but less prominence of the cheek in the parotid-masseteric region, and an antero-posteriorly smaller nose when compared with their male counterparts. The results indicated the possible phylogenetic contribution of the masticatory organ function and morphogenesis on sexual dimorphism of the human face in addition to previously reported biological and psychological characteristics, including sexual maturity, reproductive potential, mating success, general health, immune response, age, and personality.

Normal and altered masticatory load impact on the range of craniofacial shape variation: An analysis of pre-Hispanic and modern populations of the American Southern Cone

The reduction of masticatory load intensity resulting from dietary changes in human evolution has been proposed as an important factor that alters craniofacial shape in past and current populations. However, its impact on craniofacial variation and on the perceived differences among populations is unclear. The maxillomandibular relationship, which alters masticatory force direction, is a factor often neglected but it can contribute to variation in craniofacial morphology, particularly among modern/urban populations where the prevalence of dental malocclusions is greater than in prehistoric populations. This study investigates the influence of masticatory load intensity and maxillomandibular relationship as a proxy for force direction on the human craniofacial skeleton. By using 3D imaging and geometric morphometrics, we analyzed craniofacial shape variation among 186 individuals from pre-Hispanic and modern Chilean and Argentinean populations that differ in diet consistency (a proxy for masticatory load intensity) and maxillomandibular relationship. We predicted that masticatory load would have a subtle effect on the upper craniofacial bones and that this would be more marked in the maxilla. Our results showed no clear influence of masticatory load on craniofacial shape, particularly in modern/urban populations. Allometry, on the contrary, shows a stronger effect. The degree of integration between the upper craniofacial bones and the load-bearing maxilla depends on masticatory load intensity, decreasing from high to low but showing a conservative pattern of covariation among the groups. The degree of variation in the shape of the maxilla is greater than the upper craniofacial bones. These results suggest that masticatory load has a limited effect in determining differences in craniofacial morphology among populations. This effect is slightly greater for the maxillary region of the face. We propose that the reduction of functional constraints is key to greater shape variation found in modern/urban populations.

Ontogeny of the human maxilla: a study of intra-population variability combining surface bone histology and geometric morphometrics

Bone modeling is the process by which bone grows in size and models its shape via the cellular activities of the osteoblasts and osteoclasts that respectively form and remove bone. The patterns of expression of these two activities, visible on bone surfaces, are poorly understood during facial ontogeny in Homo sapiens; this is due mainly to small sample sizes and a lack of quantitative data. Furthermore, how microscopic activities are related to the development of morphological features, like the uniquely human-canine fossa, has been rarely explored. We developed novel techniques for quantifying and visualizing variability in bone modeling patterns and applied these methods to the human maxilla to better understand its development at the micro- and macroscopic levels. We used a cross-sectional ontogenetic series of 47 skulls of known calendar age, ranging from birth to 12 years, from a population of European ancestry. Surface histology was employed to record and quantify formation and resorption on the maxilla, and digital maps representing each individual's bone modeling patterns were created. Semilandmark geometric morphometric (GM) methods and multivariate statistics were used to analyze facial growth. Our results demonstrate that surface histology and GM methods give complementary results, and can be used as an integrative approach in ontogenetic studies. The bone modeling patterns specific to our sample are expressed early in ontogeny, and fairly constant through time. Bone resorption varies in the size of its fields, but not in location. Consequently, absence of bone resorption in extinct species with small sample sizes should be interpreted with caution. At the macroscopic level, maxillary growth is predominant in the top half of the bone where bone formation is mostly present. Our results suggest that maxillary growth in humans is highly constrained from early stages in ontogeny, and morphological changes are likely driven by changes in osteoblastic and osteoclastic rates of expression rather than differences in the bone modeling patterns (i.e. changes in location of formation and resorption). Finally, the results of the micro- and macroscopic analyses suggest that the development of the canine fossa results from a combination of bone resorption and bone growth in the surrounding region.

The affinities of Homo antecessor – a review of craniofacial features and their taxonomic validity

The phylogenetic affinities of Homo antecessor, a hominin dating from the early Middle Pleistocene of Europe, are still unclear. In this study we conducted a comprehensive review of the TD6 hypodigm within the context of the historical development of paleoanthropological issues concerning this species. H. antecessor, based on all available craniofacial features to date, displays a midfacial morphology very similar to specimens attributed to Classic Homo erectus, suggesting that H. antecessor is the geographical European variant of Classic H. erectus.

Ontogeny of the maxilla in Neanderthals and their ancestors

Neanderthals had large and projecting (prognathic) faces similar to those of their putative ancestors from Sima de los Huesos (SH) and different from the retracted modern human face. When such differences arose during development and the morphogenetic modifications involved are unknown. We show that maxillary growth remodelling (bone formation and resorption) of the Devil's Tower (Gibraltar 2) and La Quina 18 Neanderthals and four SH hominins, all sub-adults, show extensive bone deposition, whereas in modern humans extensive osteoclastic bone resorption is found in the same regions. This morphogenetic difference is evident by ∼5 years of age. Modern human faces are distinct from those of the Neanderthal and SH fossils in part because their postnatal growth processes differ markedly. The growth remodelling identified in these fossil hominins is shared with Australopithecus and early Homo but not with modern humans suggesting that the modern human face is developmentally derived.

Unlike modern humans, Neanderthals had large and projecting faces. Here, the authors show that the maxilla of modern humans is distinct from those of the Neanderthal and Middle Pleistocene hominins from Sima de los Huesos because their growth processes differ markedly during the postnatal period.