Bone size and shape arise throughout ontogeny as a result of the coordinated activity of osteoblasts and osteoclasts, responsible for bone deposition and resorption, and growth displacements. The modelling processes leave specific microstructural features on the bone surface, which can be used to infer the mechanisms shaping craniofacial traits in extinct and extant species. However, the analysis of bone surfaces from fossils and archaeological samples faces some difficulties related to the bone loss caused by taphonomic factors, and the lack of formal methods for estimating missing information and comparing the patterns of bone modelling among several specimens and samples. The present study provides a new approach for the quantitative analysis of bone formation and resorption patterns obtained from craniofacial surfaces. First, interpolation techniques were used to estimate missing data on high-resolution replicas of the left maxilla in a sample of sub-adult and adult modern humans and sub-adult fossil hominins. The performance of this approach was assessed by simulating variable amounts of missing data. Then, we applied measures of dispersion and central tendency to represent the variation and average pattern of bone modelling within samples. The spatial interpolation resulted in reliable estimations of the type of cell activity (deposition or resorption) in the missing areas, even when large extensions of the bone surface were lost. The quantification of the histological data allowed us to integrate the information of different specimens and depict the areas with higher and lower variation in the bone modelling pattern of the maxilla among specimens. Overall, the main advantages of the quantitative approach used here for generating bone modelling patterns are the high replicability and the possibility of incorporating variation among specimens into the comparisons among samples.

Objectives: To assess the intraspecific variation in bone remodeling patterns in modern humans, we studied two populations from southern South America that represent the extremes of morphological variation in this region. We particularly analyzed the ontogenetic changes in the patterns of bone growth remodeling and compared the patterns between samples. Materials and methods:We obtained high-resolution casts of the periosteal surface of the upper and middle face of subadults (n = 36) and adult (n = 36) individuals from a sample of hunter-gatherers from Patagonia and a sample of horticulturists from Northwest Argentina. The areas of bone formation and resorption were registered using an incident-light microscope. We then estimated the average bone remodeling map by sample and age, and performed principal component analysis and multivariate regressions to assess the extension and distribution of these areas across ontogeny and between samples. Results:We found that the remodeling pattern of the glabella, supraorbital arch, frontal process of the maxilla, and a large part of the zygomatic bone is relatively constant in subadults and adults from both sample with a clear predominance of bone formation. In contrast, the middle face is characterized by the spatial alternation between formation and resorption areas, and greater variation with age and between samples.The main differences were found in areas related to chewing and muscle insertions. Conclusions:Our study provides the first evidence of interpopulation variation in bone growth remodeling and suggests that biomechanical factors can influence the observed patterns. It also underlines the need to account for ecological factors in within and between species comparisons. K E Y W O R D Sbone formation and resorption surfaces, ontogeny, paleohistology, population variation

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