Skeletal Sexual Dimorphism Research Articles

Midface Skeletal Sexual Dimorphism: Lessons Learned from Advanced Three-dimensional Imaging in the White Population.

Facial shape is significantly influenced by the underlying facial bony skeleton. Sexual dimorphisms in these structures are crucial for craniofacial, aesthetic, and gender-affirming surgery. Previous studies have examined the orbits and upper face, but less is known about the midface. This study aimed to elucidate the sexual dimorphism in the midface region, focusing on the maxilla and zygomatic bones. A retrospective review was conducted using facial computed tomography scans from 101 White patients aged 20-79 years, using Materialise Mimics and 3-Matics for segmentation and 3D reconstruction. Measurements and statistical shape modeling of the midfacial skeleton were performed. Our results show a distinct sexual dimorphism in the midfacial skeletal structure across all age groups. Women typically had a narrower bizygomatic width by 1.5 mm (P = 0.04), a shallower maxillary depth by 1.6 mm (P < 0.01), and a midfacial vertical height that was 4 mm shorter than that of men (P = 0.018). In contrast, men exhibited a greater distance between the frontozygomatic sutures by 5.4 mm (P < 0.01), a 3-mm greater interorbitale distance (P < 0.01), and a 2.1-mm wider infraorbital foramina distance (P = 0.007). There were no significant differences in the pyriform and maxillary angles (P = 0.15 and P = 0.52, respectively). Our analysis of midfacial skeletal anatomy revealed sexual dimorphism differences. Men exhibited more pronounced facial features than women, with a broader horizontal midfacial skeleton, a longer midfacial vertical height, and greater maxillary depths compared with women.

A study of the influence of genetic variance and sex on the density and thickness of the calvarial bone in collaborative cross mice.

Bone microarchitecture is affected by multiple genes, each having a small effect on the external appearance. It is thus challenging to characterize the genes and their specific effect on bone thickness and porosity. The purpose of this study was to assess the heritability and the genetic variation effect, as well as the sex effect on the calvarial bone thickness (Ca.Th) and calvarial porosity (%PoV) using the Collaborative Cross (CC) mouse population. In the study we examined the parietal bones of 56 mice from 9 lines of CC mice. Morphometric parameters were evaluated using microcomputed tomography (μCT) and included Ca.Th and %PoV. We then evaluated heritability, genetic versus environmental variance and the sex effect for these parameters. Our morphometric analysis showed that Ca.Th and %PoV are both significantly different among the CC lines with a broad sense heritability of 0.78 and 0.90, respectively. The sex effect within the lines was significant in line IL111 and showed higher values of Ca.Th and %PoV in females compared to males. In line IL19 there was a borderline sex effect in Ca.Th in which males showed higher values than females. These results stress the complexity of sex and genotype interactions controlling Ca.Th and %PoV, as the skeletal sexual dimorphism was dependent on the genetic background. This study also shows that the CC population is a powerful tool for establishing the genetic effect on these traits.

Morphometric Examination of Scapula to Determine Sexual Dimorphism

Background and Aim: Determining the sex of an individual is possible when we apply appropriate statisticalmethods using scapular measurements. Determination of sex using scapular measurements is very useful inmedicolegal cases, natural disasters and in certain circumstances in which traditionally used bones of skeleton areeither absent or fragmented. This study aims to assess sexual dimorphism for identification purposes.Material and Methods: This study was conducted using 40 adult skeletons (25 males and 15 females) with closedepiphysis having intact and well-preserved scapulae. Scapulae were measured in millimetre for MSH, MSB, GCHand GCB with the help of the sliding calliper. For all tests, confidence level and level of significance were set at95% and 5% respectively.Results: There was a highly significant difference (P &lt; 0.001) between male and female for the mean value of allmeasurements. So it indicates the existence of strong sexual dimorphism in scapula.Conclusion: Geometric morphometrics techniques feature promising results in the evaluation of skeletal sexualdimorphism, including in the size and shape of the scapula. The results of this study are very useful for sexdetermination in forensic anthropological and medicolegal cases where skull and pelvic bones are unavailable ordamaged. The present study has confirmed that gender can be determined with high accuracy by use of scapularmeasurements.

Sexual dimorphism in the walrus mandible: comparative description and geometric morphometrics.

The modern walrus Odobenus rosmarus is characterized by marked sexual dimorphism, related to its polygynous behavior and the aggressive competition between males during the breeding season. Previous studies treated skeletal sexual dimorphism in walruses either qualitatively or with basic quantitative measurements. The present study combines a detailed qualitative comparison of male and female walrus mandibles with quantitative two-dimensional geometric morphometrics analysis (principal component analysis, Procrustes ANOVA and a linear discriminant analysis). In addition to identifying previously recognized sexually dimorphic features (e.g., convexity of the anterior margin of the mandible in adult males), our study finds new morphological differences between males and females, such as a relative dorsal expansion of the anterior part of the mandible and an accentuated concavity between the dorsal margin and the coronoid process in adult males. Both our qualitative comparisons and quantitative analyses demonstrate that sexual dimorphism as expressed in the mandible of extant walruses is statistically significant and that (variation in) mandibular morphology can be used as tool to attribute sex with a good degree of accuracy to isolated mandibles or skeletons lacking the cranium. Sexual dimorphism in walruses is directly related to their sexual behavior, characterized as aggressive in males and linked to a polygynous reproduction system. Indeed, the difference in size of the tusks between males and females but also the use of these during intraspecific fights, can reasonably account for this great mandibular morphological disparity between adult males and females, but also among different ontogenetic stages. Finally, the results obtained in the present study may serve as a starting point for assessing sexual dimorphism more in-depth and studying inter- and intraspecific variation in the mandibles of fossil walruses by identifying quantified size and shape mandibular features.

Temporal and Quantitative Transcriptomic Differences Define Sexual Dimorphism in Murine Postnatal Bone Aging.

ABSTRACTTime is a central element of the sexual dimorphic patterns of development, pathology, and aging of the skeleton. Because the transcriptome is a representation of the phenome, we hypothesized that both sex and sex‐specific temporal, transcriptomic differences in bone tissues over an 18‐month period would be informative to the underlying molecular processes that lead to postnatal sexual dimorphism. Regardless of age, sex‐associated changes of the whole bone transcriptomes were primarily associated not only with bone but also vascular and connective tissue ontologies. A pattern‐based approach used to screen the entire Gene Expression Omnibus (GEO) database against those that were sex‐specific in bone identified two coordinately regulated gene sets: one related to high phosphate–induced aortic calcification and one induced by mechanical stimulation in bone. Temporal clustering of the transcriptome identified two skeletal tissue‐associated, sex‐specific patterns of gene expression. One set of genes, associated with skeletal patterning and morphology, showed peak expression earlier in females. The second set of genes, associated with coupled remodeling, had quantitatively higher expression in females and exhibited a broad peak between 3 to 12 months, concurrent with the animals' reproductive period. Results of phenome‐level structural assessments of the tibia and vertebrae, and in vivo and in vitro analysis of cells having osteogenic potential, were consistent with the existence of functionally unique, skeletogenic cell populations that are separately responsible for appositional growth and intramedullary functions. These data suggest that skeletal sexual dimorphism arises through sex‐specific, temporally different processes controlling morphometric growth and later coupled remodeling of the skeleton during the reproductive period of the animal. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Craniofacial ontogeny in Tylosaurinae.

Mosasaurs were large, globally distributed aquatic lizards that lived during the Late Cretaceous. Despite numerous specimens of varying maturity, a detailed growth series has not been proposed for any mosasaur taxon. Two taxa—Tylosaurus proriger and T. kansasensis/nepaeolicus—have robust fossil records with specimens spanning a wide range of sizes and are thus ideal for studying mosasaur ontogeny. Tylosaurus is a genus of particularly large mosasaurs with long, edentulous anterior extensions of the premaxilla and dentary that lived in Europe and North America during the Late Cretaceous. An analysis of growth in Tylosaurus provides an opportunity to test hypotheses of the synonymy of T. kansasensis with T. nepaeolicus, sexual dimorphism, anagenesis, and heterochrony. Fifty-nine hypothetical growth characters were identified, including size-dependent, size-independent, and phylogenetic characters, and quantitative cladistic analysis was used to recover growth series for the two taxa. The results supported the synonymy of T. kansasensis with T. nepaeolicus and that T. kansasensis represent juveniles of T. nepaeolicus. A Spearman rank-order correlation test resulted in a significant correlation between two measures of size (total skull length and quadrate height) and maturity. Eleven growth changes were shared across both species, neither of the ontogram topologies showed evidence of skeletal sexual dimorphism, and a previous hypothesis of paedomorphy in T. proriger was not rejected. Finally, a novel hypothesis of anagenesis in Western Interior Seaway Tylosaurus species, driven by peramorphy, is proposed here.

Estrogen receptor alpha signaling in extrahypothalamic neurons during late puberty decreases bone size and strength in female but not in male mice.

Sexually dimorphic bone structure emerges largely during puberty. Sex steroids are critical for peak bone mass acquisition in both genders. In particular, the biphasic effects of estrogens mediate the skeletal sexual dimorphism. However, so far the stimulatory vs inhibitory actions of estrogens on bone mass are not fully explained by direct effects on bone cells. Recently, it has become evident that there is possible neuroendocrine action of estrogen receptor alpha (ERα) on the skeleton. Based on these considerations, we hypothesized that neuronal ERα-signaling may contribute to the skeletal growth during puberty. Here, we generated mice with tamoxifen-inducible Thy1-Cre mediated ERα inactivation during late puberty specifically in extrahypothalamic neurons (N-ERαKO). Inactivation of neuronal ERα did not alter the body weight in males, whereas N-ERαKO females exhibited a higher body weight and increased body and bone length compared to their control littermates at 16weeks of age. Ex vivo microCT analysis showed increased radial bone expansion of the midshaft femur in female N-ERαKO along with higher serum levels of insulin-like growth factor (IGF)-1 as well as IGF-binding protein (IGFBP)-3. Furthermore, the 3-point bending test revealed increased bone strength in female N-ERαKO. In contrast, inactivation of neuronal ERα had no major effect on bone growth in males. In conclusion, we demonstrate that central ERα-signaling limits longitudinal bone growth and radial bone expansion specifically in females potentially by interacting with the GH/IGF-1 axis.

Regulation of the Bone Vascular Network is Sexually Dimorphic.

ABSTRACTOsteoblast (OB) lineage cells are an important source of vascular endothelial growth factor (VEGF), which is critical for bone growth and repair. During bone development, pubertal differences in males and females exist, but little is known about whether VEGF signaling contributes to skeletal sexual dimorphism. We have found that in mice, conditional disruption of VEGF in osteocalcin‐expressing cells (OcnVEGFKO) exerts a divergent influence on morphological, cellular, and whole bone properties between sexes. Furthermore, we describe an underlying sexual divergence in VEGF signaling in OB cultures in vitro independent of circulating sex hormones. High‐resolution synchrotron computed tomography and backscattered scanning electron microscopy revealed, in males, extensive unmineralized osteoid encasing enlarged blood vessel canals and osteocyte lacunae in cortical bone after VEGF deletion, which contributed to increased porosity. VEGF was deleted in male and female long bone–derived OBs (OBVEGKO) in vitro and Raman spectroscopic analyses of mineral and matrix repertoires highlighted differences between male and female OBVEGFKO cells, with increased immature phosphate species prevalent in male OBVEGFKO cultures versus wild type (WT). Further sexual dimorphism was observed in bone marrow endothelial cell gene expression in vitro after VEGF deletion and in sclerostin protein expression, which was increased in male OcnVEGFKO bones versus WT. The impact of altered OB matrix composition after VEGF deletion on whole bone geometry was assessed between sexes, although significant differences between OcnVEGFKO and WT were identified only in females. Our results suggest that bone‐derived VEGF regulates matrix mineralization and vascularization distinctly in males and females, which results in divergent physical bone traits.

The Influence of Body Size on the Expression of Sexually Dimorphic Morphological Traits

Skeletal sexual dimorphism manifests as size or shape differences between males and females in a population. Certain dimorphic traits are used in sex estimation methods, and populational variation in the expression of these traits can result in inaccurate sex estimation. However, the underlying causes of variation in trait expression remain unclear. This study explores body size, which also exhibits sexual dimorphism, as a potential factor influencing trait expression. To test this, skeletons of 209 individuals of varying body size were analyzed, and morphological traits were scored according to the Walker (2008), Klales et al. (2012), and Rogers (1999) sex estimation methods. Statistical analyses found significant correlations between body size parameters and expression of traits, with stature explaining more relative variance in trait expression than body mass. However, the relationships are weak and few in number, suggesting that body size has a minimal impact on the expression of these morphological traits.

Population variation in skeletal sexual dimorphism

Research has documented considerable population variation in sexual dimorphism related to human growth and development. This variation represents both genetic and environmental factors which impact methodologies used to estimate sex from human skeletal remains. This article provides an overview of known variation in skeletal sexual dimorphism among populations through documented research on samples from around the world. Variation in juvenile growth patterns of populations and differences in adult skeletal size and characteristics are discussed. This recognized variation should be considered by forensic anthropologists when estimating sex from skeletal remains and appropriate population-specific data should be utilized.

Sex determination based on sacral and coccygeal measurements using multidetector computed tomography in a contemporary Japanese population

Abstract Sex determination is an integral and foremost step in determining the identity of an unknown individual. The present study aimed to examine skeletal sexual dimorphism of the sacrum and coccyx using computed tomography (CT) images in a contemporary Japanese population and to derive discriminant function formulae for sex determination. Data were collected from 230 cadavers (115 male and 115 female subjects) subjected to postmortem CT scanning and subsequent forensic autopsy. Seven measurements of the sacrum and coccyx were obtained from CT images of each subject. The measurements were analyzed using descriptive statistics and discriminant function analyses. All except one measurement exhibited statistically significant sexual dimorphism, and the maximum sex determination rate was 83.5% according to discriminant function analyses. The results of this study suggest that discriminant analysis of sacral and coccygeal traits may be useful for the sex determination of skeletal remains in the Japanese population when applied with additional methods, such as morphological trait evaluation of other available bones.

Specialization for aggression in sexually dimorphic skeletal morphology in grey wolves (Canis lupus).

Aggressive behaviour is important in the life history of many animals. In grey wolves (Canis lupus), territory defence through direct competition with conspecifics is severe and often lethal. Thus, performance in aggressive encounters may be under strong selection. Additionally, grey wolves frequently kill large dangerous prey species. Because both sexes actively participate in aggressive activities and prey capture, wolves are expected to exhibit a low level of musculoskeletal sexual dimorphism. However, male wolves more often lead in agonistic encounters with conspecifics and must provision the nursing female during the pup-rearing period of the breeding season. These behaviours may select for males that exhibit a higher degree of morphological adaptation associated with aggression and prey capture performance. To test this prediction, we assessed skeletal sexual dimorphism in three subspecies of grey wolves using functional indices reflecting morphological specialization for aggression. As expected, sexual dimorphism in skeletal shape was limited. However, in two of three subspecies, we found sexually dimorphic traits in the skull, forelimbs and hindlimbs that are consistent with the hypothesis that males are more specialized for aggression. These characters may also be associated with selection for improved prey capture performance by males. Thus, the sexually dimorphic functional traits identified by our analysis may be adaptive in the contexts of both natural and sexual selection. Several of these traits may conflict with locomotor economy, indicating the importance of aggression in the life history of male grey wolves. The presence of functional specialization for aggression in a generally monogamous species indicates that sexual dimorphism in specific musculoskeletal traits may be widespread among mammals.

Sex and the single nucleotide polymorphism: Exploring the genetic causes of skeletal sex differences

Skeletal traits are exemplars of sexual dimorphism, with consistent sex differences across populations in bone mineral density (BMD), bone geometry, and osteoporotic fracture risk.(1–3) Heritability of these traits has also been demonstrated, and many common single nucleotide polymorphisms (SNP) have pointed to genes accounting for variability in BMD and fracture risk.(4–6) These observations beg the question whether genetic variation affects the female skeleton differently than it does the male. Because testing such gene-by-sex interactions for common SNPs in genome-wide association studies requires extraordinarily large sample sizes, the analysis has only recently become possible with the collaboration of investigators in the GEFOS consortium and other independent studies.(7) Their report follows on recent triumphs such as the GWAS meta-analysis of BMD in more than 80,000 men and women in GEFOS/GENOMOS cohorts(6) that identified 56 genes, several of which were also associated with fracture. Gene-by-sex interactions could identify new signals not detected in the sex-combined analyses and indicate important sex-dependent skeletal biology. Liu and colleagues(7) report that, in fact, no sex differences in the effects of autosomal SNPs on BMD were found in an analysis of more than 50,000 men and women. The contributions of this well designed study and what remains to be explored—beyond SNPs and BMD—to explain genetic causes of skeletal sexual dimorphism are the focus of our discussion. Multiple reports of sex differences in heritability and genetic associations with human skeletal traits have been reported (reviewed in Karasik and Ferrari(8)), including a large meta-analysis of BMD quantitative trait loci (QTL) in humans and SNP association studies for important candidates such as LRP5 and ESR1. There are well recognized limitations of this body of evidence, several of which are addressed by the study from Liu and colleagues.(7) First, although genetic associations discovered in only one sex might, in fact, point to sex-dependent effects, they may also be the result of a lack of power to detect what is truly the same underlying effect in each of the sex strata. In many cases, sex-specific effects have been reported without formally testing the difference in effect between the sexes. In the current study, the investigators have conducted the most comprehensive and well designed study to test that genetic polymorphisms have a different effect on BMD in men than they have in women. Second, as with many studies of sex differences, few replication studies have been published.(9) Publication bias is a well recognized impediment to the consideration of negative results (ie, findings of no sex differences in QTLs or genetic associations) and, in fact, a few other studies have found no significant sex differences in BMD genetic variance(10) or in genotypic effects on BMD.(7) This bias is a problem that meta-analyses, such as the one by Liu and colleagues, take strides against by aligning multiple cohorts and reporting no evidence of gene-by-sex interactions. It is tempting to imagine that with even larger sample sizes statistically significant gene-by-sex interactions might emerge in human cohorts. However, given the small detectable effect sizes noted by Liu and colleagues (explaining <1% of variation in BMD), it is likely to be more rewarding to turn to explanations for the dimorphism that are not based on differential effects of common autosomal SNPs between the sexes. If sequence analysis delivers on the promise of larger effect sizes, it might indeed be possible to document gene-by-sex interactions in future studies. Studies of several genetic mechanisms that were not explored in the study by Liu and colleagues might provide additional insight.

Effects of neonatal castration and androgenization on sexual dimorphism in bone, leptin and corticosterone secretion

This study investigated the role of neonatal sex steroids in rats on sexual dimorphism in bone, as well as on leptin and corticosterone concentrations throughout the lifespan. Castration of males and androgenization of females were used as models to investigate the role of sex steroids shortly after birth. Newborn Wistar rats were divided into four groups, two male groups and two female groups. Male pups were cryoanesthetized and submitted to castration or sham-operation procedures within 24h after birth. Female pups received a subcutaneous dose of testosterone propionate (100μg) or vehicle. Rats were euthanized at 20, 40, or 120 postnatal days. Body weight was also measured at 20, 40, and 120days of age, and blood samples and femurs were collected. The length and thickness of the femurs were measured and the areal bone mineral density (areal BMD) was determined by dual-energy X-ray absorptiometry (DEXA). Biomechanical three-point bending testing was used to evaluate bone breaking strength, energy to fracture, and extrinsic stiffness. Blood samples were submitted to a biochemical assay to estimate calcium, phosphorus, alkaline phosphatase, leptin, and corticosterone levels. Weight gain, areal BMD and bone biomechanical properties increased rapidly with respect to age in all groups. In control animals, skeletal sexual dimorphism, leptin concentration, and dimorphic corticosterone concentration patterns were evident after puberty. However, androgen treatment induced changes in growth, areal BMD, and bone mass properties in neonatal animals. In addition, neonatally-castrated males had bone development and mechanical properties similar to those of control females. These results suggest that the exposure to neonatal androgens may represent at least one covariate that mediates dimorphic variation in leptin and corticosterone secretions. The study indicates that manipulation of the androgen environment during the critical period of sexual differentiation of the brain causes long-lasting changes in bone development, as well as serum leptin and corticosterone concentrations. In addition, this study provides useful models for the investigation of bone disorders induced by hypothalamic hypogonadism.

Skeletal sexual dimorphism: relative contribution of sex steroids, GH–IGF1, and mechanical loading

Structural gender differences in bone mass - characterized by wider but not thicker bones - are generally attributed to opposing sex steroid actions in men and women. Recent findings have redefined the traditional concept of sex hormones as the main regulators of skeletal sexual dimorphism. GH-IGF1 action is likely to be the most important determinant of sex differences in bone mass. Estrogens limit periosteal bone expansion but stimulate endosteal bone apposition in females, whereas androgens stimulate radial bone expansion in males. Androgens not only act directly on bone through the androgen receptor (AR) but also activate estrogen receptor-α or -β (ERα or ERβ) following aromatization into estrogens. Both the AR and ERα pathways are needed to optimize radial cortical bone expansion, whereas AR signaling alone is the dominant pathway for normal male trabecular bone development. Estrogen/ERα-mediated effects in males may - at least partly - depend on interaction with IGF1. In addition, sex hormones and their receptors have an impact on the mechanical sensitivity of the growing skeleton. AR and ERβ signaling may limit the osteogenic response to loading in males and females respectively, while ERα may stimulate the response of bone to mechanical stimulation in the female skeleton. Overall, current evidence suggests that skeletal sexual dimorphism is not just the end result of differences in sex steroid secretion between the sexes, but depends on gender differences in GH-IGF1 and mechanical sensitivity to loading as well.

Sexual dimorphism in cortical bone size and strength but not density is determined by independent and time-specific actions of sex steroids and IGF-1: Evidence from pubertal mouse models

Although it is well established that males acquire more bone mass than females, the underlying mechanism and timing of this sex difference remain controversial. The aim of this study was to assess the relative contribution of sex steroid versus growth hormone-insulin-like growth factor 1 (GH-IGF-1) action to pubertal bone mass acquisition longitudinally in pubertal mice. Radial bone expansion peaked during early puberty (3 to 5 weeks of age) in male and female mice, with significantly more expansion in males than in females (+40%). Concomitantly, in 5 week old male versus female mice, periosteal and endocortical bone formation was higher (+70%) and lower (-47%), respectively, along with higher serum IGF-1 levels during early puberty in male mice. In female mice, ovariectomy increased radial bone expansion during early puberty as well as the endocortical perimeter. In male mice, orchidectomy reduced radial bone expansion only during late puberty (5 to 8 weeks of age), whereas combined androgen and estrogen deficiency modestly decreased radial bone expansion during early puberty, accompanied by lower IGF-1 levels. GHRKO mice with very low IGF-1 levels, on the other hand, showed limited radial bone expansion and no skeletal dimorphism. From these data we conclude that skeletal sexual dimorphism is established during early puberty and depends primarily on GH-IGF-1 action. In males, androgens and estrogens have stimulatory effects on bone size during late and early puberty, respectively. In females, estrogens limit bone size during early puberty. These longitudinal findings in mice provide strong evidence that skeletal dimorphism is determined by independent and time-specific effects of sex steroids and IGF-1.

Gough's Cave 1 (Somerset, England): an Assessment of the Sex and Age at Death

The overall impression of the sexually dimorphic characteristics of Gough's Cave 1 is that the remains are those of a male. However, the specimen does present some ‘female’ features in the facial skeleton, the ischiopubic rami and pelvic apertures, combined with relatively small overall size, and an ambiguous greater sciatic notch morphology. Nevertheless, the various features employed for sexual diagnosis of Gough's Cave are predominantly those which indicate or strongly suggest that it is male, but this must be accompanied with the caveat that either this individual falls at the feminine end of the male range of variation or that the patterns of skeletal sexual dimorphism of the population from which it derived were modestly different from those of the mostly European and European-derived reference samples used for this assessment. In contrast to the ambiguities of sex determination for Gough's Cave 1, the various indicators of his age-at-death are highly consistent. All of them agree in placing Gough's Cave 1 between his late second decade and middle third decade. He was unlikely to have been younger than about 18 years, and most likely was not older than about 23 years at death.

Original tomographic analysis (pQCT) of the human skeletal sexual dimorphism as diagnostic reference

Original tomographic analysis (pQCT) of the human skeletal sexual dimorphism as diagnostic reference

Mandibular ramus posterior flexure: a sex indicator in Homo sapiens fossil hominids?

Accurate determination of sex in skeletal human samples is very important in anthropological and demographic studies. Recently, Loth and Henneberg have suggested that a new osteological criterion on the mandible, the mandibular ramus posterior flexure (MRPF) had a high sex discriminating effectiveness. A preliminary test applied to a few hominid mandibles )including Australopithecines, Homo erectus, Neanderthals and Upper palaeolithic hominids) apparently confirmed the high reliability of the MRPF as a sex indicator ‘over time and through palaeospecies’. As the pelvis is commonly considered as providing the most significant criteria that allows the establishment of skeletal sexual dimorphism of adults, the present paper evaluates this mandibular feature on a few additional palaeolithic hominids (i.e. Neanderthals and Early Modern Humans) for whom a gender estimation was known based upon the pelvis. This analysis was conducted on the original material and its results appear in contradiction with those of the previous studies made by Loth and Henneberg. A reconsideration of the visual assessment of MRPF as a sex indicator in Homo sapiens fossil hominids is therefore suggested. Copyright © 2000 John Wiley & Sons, Ltd.

Temporal trends and metric variation in the mandibles and dentition of Australopithecus afarensis

The Pliocene hominin samples from Hadar and Laetoli are thought to represent one species,Australopithecus afarensis , that exhibits stasis throughout its temporal range and has high levels of skeletal sexual dimorphism. In this paper, we test the hypothesis of stasis in dental and mandibular dimensions using nonparametric rank correlation methods to detect temporal trends and randomization tests to evaluate their statistical significance. We then use two methods (CV resampling; Fligner–Killeen test) to compare overall levels of variation in the fossil sample to those of extant hominoid species. Together, these analyses allow us to gauge the effects of changes through time on variation in mandibles and teeth of A. afarensis.P3mesiodistal length, M3size, and canine shape change through time but do not appear unusually variable in the sample as a whole. These temporal trends possibly reflect differences between the Laetoli and Hadar site-samples. For mandibles, a pronounced trend towards greater corpus size occurs late in the temporal sequence and contributes to high levels of variation compared to African apes. These results show that significant directional changes do occur in the A. afarensis mandibles and teeth, and in these elements, at least, the species is not static. Temporal variation is clearly an important component of overall variation in the A. afarensis lineage, even though other factors, such as sexual dimorphism, may also play a part.