Comparisons of age-at-death distributions among extinct hominins and extant nonhuman primates indicate normal mortality

Acknowledgements The authors wish to thank the anonymous reviewers and the editor for their constructive and helpful feedback, which has undoubtedly improved this manuscript.Peer reviewedPostprin

Sagittal crest formation in great apes and gibbons

The frequency of sagittal crest expression and patterns of sagittal crest growth and development have been documented in hominoids, including some extinct hominin taxa, and the more frequent expression of the sagittal crest in males has been traditionally linked with the need for larger-bodied individuals to have enough attachment area for the temporalis muscle. In the present study, we investigate sagittal cresting in a dentally mature sample of four hominoid taxa (Pan troglodytes schweinfurthii, Gorilla gorilla gorilla, Pongo pygmaeus pygmaeus and Hylobates lar). We investigate whether sagittal crest size increases with age beyond dental maturity in males and females of G. g. gorilla and Po. pyg. pygmaeus, and whether these taxa show sex differences in the timing of sagittal crest development. We evaluate the hypothesis that the larger sagittal crest of males may not be solely due to the requirement for a larger surface area than the un-crested cranial vault can provide for the attachment of the temporalis muscle, and present data on sex differences in temporalis muscle attachment area and sagittal crest size relative to cranial size. Gorilla g. gorilla and Po. pyg. pygmaeus males show significant relationships between tooth wear rank and sagittal crest size, and they show sagittal crest size differences between age groups that are not found in females. The sagittal crest emerges in early adulthood in the majority of G. g. gorilla males, whereas the percentage of G. g. gorilla females possessing a sagittal crest increases more gradually. Pongo pyg. pygmaeus males experience a three-fold increase in the number of specimens exhibiting a sagittal crest in mid-adulthood, consistent with a secondary growth spurt. Gorilla g. gorilla and Po. pyg. pygmaeus show significant sex differences in the size of the temporalis muscle attachment area, relative to cranial size, with males of both taxa showing positive allometry not shown in females. Gorilla g. gorilla males also show positive allometry for sagittal crest size relative to cranial size. Our results suggest that although patterns of sagittal crest expression have limited utility for taxonomy and phylogeny reconstruction, they could be useful for reconstructing aspects of social behaviour in some extinct hominin taxa. In particular, our results in G. g. gorilla and Po. pyg. pygmaeus, which suggest that the size of sagittal crests in males cannot be solely explained by the surface area required for attachment of the temporalis muscle, offer partial support for the hypothesis that large sagittal crests form in response to sexual selection and may play a role in social signalling

Nanostructure-specific X-ray tomography reveals myelin levels, integrity and axon orientations in mouse and human nervous tissue

Myelin insulates neuronal axons and enables fast signal transmission, constituting a key component of brain development, aging and disease. Yet, myelin-specific imaging of macroscopic samples remains a challenge. Here, we exploit myelin’s nanostructural periodicity, and use small-angle X-ray scattering tensor tomography (SAXS-TT) to simultaneously quantify myelin levels, nanostructural integrity and axon orientations in nervous tissue. Proof-of-principle is demonstrated in whole mouse brain, mouse spinal cord and human white and gray matter samples. Outcomes are validated by 2D/3D histology and compared to MRI measurements sensitive to myelin and axon orientations. Specificity to nanostructure is exemplified by concomitantly imaging different myelin types with distinct periodicities. Finally, we illustrate the method’s sensitivity towards myelin-related diseases by quantifying myelin alterations in dysmyelinated mouse brain. This non-destructive, stain-free molecular imaging approach enables quantitative studies of myelination within and across samples during development, aging, disease and treatment, and is applicable to other ordered biomolecules or nanostructures

Sexual dimorphism, growth and development beyond dental maturity in the cranium of extant hominoid primates

Sexual size dimorphism is a useful predictor of sociality in primates based on the association between male intrasexual competition and male size, relative to female size. Less considered ideas include the relationship between sexual dimorphism of facial traits and socioecological variability and the notion that females may obtain reproductive advantages from larger body size or facial morphology, similar to what is observed in males. In the present research, I investigate the morphological correlates of social and non-social variables to understand whether the facial skeleton, including the sagittal crest, carries a social signal. I adopt the heterochronic framework advocated by Shea (1986) to understand how sexual dimorphism is attained. I examine craniofacial size and shape dimorphism, growth and development in five extant hominoid primate taxa (Homo sapiens, Pan t. schweinfurthii, Gorilla g. gorilla, Pongo p. pygmaeus and Hylobates lar) to understand whether sex-specific patterns of facial dimorphism, growth and development are associated with social and life history variables. I use 3D surface data to quantify cranial size and shape using 3D co-ordinate landmarks, surface area data and linear measurements. Geometric morphometric techniques are used to calculate size and shape variables, including Procrustes distances between male and female average shapes, and visualisation of shape differences using Principal component scores. Marital system explains a small, but significant, amount of craniofacial size and shape variation in modern humans, and patterns of shape dimorphism in the brow ridge of Pan t. schweinfurthii and Gorilla g. gorilla, and in the mid-face of Gorilla g. gorilla and Pongo p. pygmaeus, indicate that sex-specific shape of these regions may be morphologically conserved. Sagittal crest emergence in Gorilla g. gorilla and Pongo p. pygmaeus males cannot be explained by mastication alone and is likely to be, in part, a result of sexual selection. Future studies, adopting a heterochronic approach to sexual dimorphism, are likely to afford detailed inferences about the relationship between morphological and behavioural variables and may have applications in reconstructing extinct hominoid social behaviour

Sagittal crest formation in great apes and gibbons

The frequency of sagittal crest expression and patterns of sagittal crest growth and development have been documented in hominoids, including some extinct hominin taxa, and the more frequent expression of the sagittal crest in males has been traditionally linked with the need for larger-bodied individuals to have enough attachment area for the temporalis muscle. In the present study, we investigate sagittal cresting in a dentally mature sample of four hominoid taxa (Pan troglodytes schweinfurthii, Gorilla gorilla gorilla, Pongo pygmaeus pygmaeus and Hylobates lar). We investigate whether sagittal crest size increases with age beyond dental maturity in males and females of G. g. gorilla and Po. pyg. pygmaeus, and whether these taxa show sex differences in the timing of sagittal crest development. We evaluate the hypothesis that the larger sagittal crest of males may not be solely due to the requirement for a larger surface area than the un-crested cranial vault can provide for the attachment of the temporalis muscle, and present data on sex differences in temporalis muscle attachment area and sagittal crest size relative to cranial size. Gorilla g. gorilla and Po. pyg. pygmaeus males show significant relationships between tooth wear rank and sagittal crest size, and they show sagittal crest size differences between age groups that are not found in females. The sagittal crest emerges in early adulthood in the majority of G. g. gorilla males, whereas the percentage of G. g. gorilla females possessing a sagittal crest increases more gradually. Pongo pyg. pygmaeus males experience a three-fold increase in the number of specimens exhibiting a sagittal crest in mid-adulthood, consistent with a secondary growth spurt. Gorilla g. gorilla and Po. pyg. pygmaeus show significant sex differences in the size of the temporalis muscle attachment area, relative to cranial size, with males of both taxa showing positive allometry not shown in females. Gorilla g. gorilla males also show positive allometry for sagittal crest size relative to cranial size. Our results suggest that although patterns of sagittal crest expression have limited utility for taxonomy and phylogeny reconstruction, they could be useful for reconstructing aspects of social behaviour in some extinct hominin taxa. In particular, our results in G. g. gorilla and Po. pyg. pygmaeus, which suggest that the size of sagittal crests in males cannot be solely explained by the surface area required for attachment of the temporalis muscle, offer partial support for the hypothesis that large sagittal crests form in response to sexual selection and may play a role in social signalling. Key words: cranium; ectocranial cresting; hominoid; sexual dimorphism; sexual selection.Financial support for K.L.B. was provided by an NERC/ESRC Interdisciplinary studentship, a Leakey Trust Small Grant, a Gay Clifford Research Award for Outstanding Women Students awarded by the UCL Graduate School, and GW’s Provost

Mandibular corpus shape is a taxonomic indicator in extant hominids

Objectives: The aim of this study is to understand whether the shape of three subregions of the mandibular corpus (the alveolar arch, corpus at M1 and posterior symphysis) are useful for making taxonomic assessments at the genus and species levels in extant hominids. Materials and Methods: We use data taken from 3D surface scans of the mandibular corpus of seven extant hominid taxa: Gorilla gorilla gorilla, Gorilla beringei graueri, Homo sapiens, Pan paniscus, Pan troglodytes schweinfurthii, Pongo abelii, and Pongo pygmaeus pygmaeus to generate four shape variables: alveolar arch shape (AAS), corpus shape at M1 (CSM1), posterior symphysis shape at the midline (PSSM), and posterior symphysis shape (PSS). To ascertain how reliable each mandibular shape variable is for assessing taxonomy, we ran canonical discriminant and discriminant function analysis, reporting cross-validated results. Results: Using a combination of three mandibular corpus shape variables, 99% of specimens were classified correctly for genus-level analyses. A maximum of 100% of Pan specimens, 94% of Gorilla specimens and 96% of Pongo specimens were classified correctly at the species level when up to three mandibular shape variables were included in the analyses. When mandibular corpus variables were considered in isolation, posterior symphysis shape yielded the highest overall correct classification results. Discussion: The high taxonomic classification rates at both the genus and species level, using 3D surface data and advanced quantification techniques, show that the shape of the alveolar arch, corpus at M1 and symphysis can distinguish extant hominid taxa. These findings have implications for assessing the taxonomy of extinct hominid specimens which preserve these mandibular sub-regions.These scans were acquired through the generous support of the Smithsonian 2.0 Fund and the Smithsonian's Collections Care and Preservation Fund

Integration between the face and the mandible of Pongo and the evolution of the craniofacial morphology of orangutans

Objectives Extant Pongo diverges from other hominids by a series of craniofacial morphological features, such as a concave face, a reduced supraorbital torus, or an upwardly orientated palate. These traits are not independent because the skull is a complex integrated structure. The aim of this study is to describe the relationship between the face and mandible of Pongo, in order to examine the link between mandibular structures and the set-up of the unique facial features of orangutans. Materials and methods Using 3D geometric morphometrics, the morphological integration between face and mandible of Pongo is compared to that of the three extant hominids: Homo, Pan, and Gorilla. Pooled within-species partial least squares analyses are computed in order to quantify the patterns and levels of integration. Results The covariation analyses show unique patterns of integration and levels of correlation in Pongo when compared to other hominids. This study shows that the craniofacial features distinguishing Pongo from African great apes are related to differences in the patterns of integration and levels of correlation between facial and mandibular shape. Discussion Changes in important functions may play a part in these modifications of craniofacial integration. This study underlines the importance of the mandible and of the mandibular functions in the development of the unique craniofacial features of Pongo. Am J Phys Anthropol 158:475-486, 2015.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe