Differential sexual dimorphism: size and shape in the cranium and pelvis of grey foxes (Urocyon)

Patterns of sexual size dimorphism (SSD) and cranial dimorphism are well documented. However, limited examinations exist of the contrasts in the patterns and nature of dimorphism across body regions (e.g. cranium, pelvis), particularly when these regions have different sex-specific functions (e.g. display in mating, locomotion, and reproduction). Using landmark-based morphometric techniques, we investigated size and shape dimorphism variation in the crania and pelves of two closely-related fox species within the genus Urocyon . Although we found no significant size and shape dimorphism in the crania of either species, we did find significant dimorphism in the pelvis: its size was dimorphic in Urocyon littoralis (but not in Urocyon cinereoargenteus ) and its shape was dimorphic in both species (though more pronounced in U. littoralis ). The observation of greater dimorphism in the pelvis than in the cranium suggests that factors such as offspring size and locomotor mode play a greater role in sexual dimorphism than simple 'whole body' allometric affects associated with dimorphism in body size.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 339–353.     

Sexual dimorphism in Southeast Asian crania: A geometric morphometric approach

Despite a number of studies stating that sexual dimorphism is population specific, sexual differences in Southeast Asian populations have received little attention. Previous studies in this region have focused on samples from Thailand or East Asian populations from China and Japan, examining sexual dimorphism predominantly of the postcranial bones, teeth and mandible with comparatively few cranial studies. These earlier studies have used traditional methods to metrically assess differences between the sexes. The aim of this study is to use geometric morphometric methods for the first time to quantify sexual dimorphism of Southeast Asian crania and extend knowledge of cranial sexual dimorphism beyond China, Japan and Thailand. A total of 35 unilateral and midline landmark coordinates were collected from 144 mainland and island Southeast Asian crania (89 male, 55 female). Using the shape analysis software Morphologika, principal components analysis and thin plate splines allowed for the statistical and visual exploration of shape differences. Differences included relative facial breadth, particularly across the zygomatic and postorbital regions and cranial vault breadth. Significant size dimorphism was also apparent. Overall expected accuracies were highest in the discriminant analysis using both shape and centroid size (86.8%).     

Sexual differences in European Neanderthal crania with special reference to the Krapina remains

Problems relating to the identification of sex in Neanderthal specimens are discussed. Three morphological features—morphology of the mastoid process and surrounding area, form of the supraorbital torus at glabella and the superciliary region, and the rugosity of the nuchal plane—were selected as most indicative of sex in Neanderthal crania based on observations from the Krapina collection and on those European specimens with pelvicly determined sex. Thirteen Neanderthal crania (eight males, five females) are sexed on the basis of these criteria, and the pattern and degree of sexual dimorphism determined for this sample is compared to those exhibited by other samples of more recent European hominids. It is concluded that the degree of sexual dimorphism in Neanderthal crania, as defined by this study, is consistent with that observed in the other fossil samples and that Neanderthals exhibit slightly more cranial sexual dimorphism than more recent Europeans. Models for explaining this are discussed as is the difference in pattern of change and degree of sexual dimorphism between the cranium and postcranium during later prehistoric hominid evolution in Europe.     

Exploring sexual dimorphism of human occipital and temporal bones through geometric morphometrics in an identified Western-European sample

Sex estimation is a paramount step of bioprofiling in both forensic anthropology and osteoarchaeology. When the pelvis is not optimally preserved, anthropologists commonly rely on the cranium to accurately estimate sex. Over the last decades, the geometric morphometric (GM) approach has been used to determine sexual dimorphism of the crania, in size and shape, overcoming some difficulties of traditional visual and metric methods. This article aims to investigate sexual dimorphism of the occipital and temporal region through GM analysis in a metapopulation of 50 Western-European identified individuals. Statistical analyses were performed to compare centroid size and shape data between sexes through the examination of distinct functional modules. Regression and Procrustes ANOVA were used to examine allometric and asymmetrical implications. Discriminant functions, combining size and shape data, were established. Significant dimorphism in size was found, with males having larger crania, confirming the major influence size has on cranial morphology. Allometric relationships were found to be statistically significant in both right and left temporal bones while shape differences between sexes were only significant on the right temporal bone. The visualization of the mean consensus demonstrated that males displayed a larger mastoid process associated with a reduced mastoid triangle and less projected occipital condyles. This exploratory study confirms that GM analysis represents an effective way to quantitatively capture shape of dimorphic structures, even on complex rounded ones such as the mastoid region. Further examination in a larger sample would be valuable to design objective visualization tools that can improve morphoscopic sex estimation methods.     

Sexual dimorphism and discriminant function sexing in indigenous South African crania

This study aimed to examine sexual dimorphism in, and to produce a practical discriminant function for determining the sex of indigenous, Bantu-speaking, South African crania. The types of data to be used were a small number of traditional, or mathematically transformed three-dimensional, linear measurements, comparable to those in use by most physical and forensic anthropologists. The samples to be examined, separately and pooled, were of the Cape Nguni, Natal Nguni and Sotho subgroups. In addition, three local populations (‘tribes’—Zulu, Xhosa and Southern Sotho) within these subgroups were also studied.

Univariate male/female ratios indicate significant sexual dimorphism in the pooled South African crania. Canonical variates analysis of the pooled sample showed that facial width is the strongest discriminating morphometric variable; cranial length and basi-bregmatic height are the next most significant features. Eight measurements derived from the three-dimensional data were used to produce a series of discriminant functions for sex determination in the pooled sample, for which an accuracy of 77–80% was attained. Analysis of the calvaria and face, separately, has shown that the sex of damaged material can be diagnosed with a reasonable degree of accuracy (75–76%).

The new functions for the pooled indigenous South African sample provide improved sex discrimination accuracy compared to those obtained by employing the commonly utilised statistics of Giles & Elliot (1963), even when a modified sectioning point is used. Functions calculated for the separate local populations gave variable and fairly low improvements in sexing accuracy. As the subdivisions at all levels are at present quite rapidly disappearing in South Africa, for most purposes it is now best to simply apply the pooled data functions for sexing crania.     

Biometric evidence that sexual selection has shaped the hominin face

We consider sex differences in human facial morphology in the context of developmental change. We show that at puberty, the height of the upper face, between the lip and the brow, develops differently in males and females, and that these differences are not explicable in terms of sex differences in body size. We find the same dimorphism in the faces of human ancestors. We propose that the relative shortening in men and lengthening in women of the anterior upper face at puberty is the mechanistic consequence of extreme maxillary rotation during ontogeny. A link between this developmental model and sexual dimorphism is made for the first time, and provides a new set of morphological criteria to sex human crania. This finding has important implications for the role of sexual selection in the evolution of anthropoid faces and for theories of human facial attractiveness.     

Cranial integration in Homo: singular warps analysis of the midsagittal plane in ontogeny and evolution

This study addresses some enduring issues of ontogenetic and evolutionary integration in the form of the hominid cranium. Our sample consists of 38 crania: 20 modern adult Homo sapiens, 14 sub-adult H. sapiens, and four archaic Homo. All specimens were CT-scanned except for two infant H. sapiens, who were imaged by MR instead. For each specimen 84 landmarks and semi-landmarks were located on the midsagittal plane and converted to Procrustes shape coordinates. Integration was quantified by the method of singular warps, a new geometric-statistical approach to visualizing correlations among regions. The two classic patterns of integration, evolutionary and ontogenetic, were jointly explored by comparing analyses of overlapping subsamples that span ranges of different hypothetical factors. Evolutionary integration is expressed in the subsample of 24 adult Homo, and ontogenetic integration in the subsample of 34 H. sapiens. In this data set, vault, cranial base, and face show striking and localized patterns of covariation over ontogeny, similar but not identical to the patterns seen over evolution. The principal differences between ontogeny and phylogeny pertain to the cranial base. There is also a component of cranial length to height ratio not reducible to either process. Our methodology allows a separation of these independent processes (and their impact on cranial shape) that conventional methods have not found.     

A new OH5 reconstruction with an assessment of its uncertainty

The OH5 cranium, holotype of Paranthropus boisei consists of two main portions that do not fit together: the extensively reconstructed face and a portion of the neurocranium. A physical reconstruction of the cranium was carried out by Tobias in 1967, who did not discuss problems related to deformation, although he noted a slight functional asymmetry. Nevertheless, the reconstructed cranium shows some anomalies, mainly due to the right skewed position of the upper calvariofacial fragment and uncertainty of the relative position of the neurocranium to the face, which hamper further quantitative analysis of OH5′s cranial geometry. Here, we present a complete virtual reconstruction of OH5, using three-dimensional (3D) digital data, geometric morphometric (GM) methods and computer-aided design (CAD) techniques. Starting from a CT scan of Tobias’s reconstruction, a semi-automatic segmentation method was used to remove Tobias’s plaster. The upper calvariofacial fragment was separated from the lower facial fragment and re-aligned using superposition of their independent midsagittal planes in a range of feasible positions. The missing parts of the right hemiface were reconstructed using non-uniform rational basis-spline (NURBS) surface and subsequently mirrored using the midsagittal plane to arrive at a symmetrical facial reconstruction. A symmetric neurocranium was obtained as the average of the original shape and its mirrored version. The alignment between the two symmetric shapes (face and neurocranium) used their independent midsagittal plane and a reference shape (KNM-ER 406) to highly reduce their degrees of freedom. From the series of alternative reconstructions, we selected the middle of this rather small feasible range. When reconstructed as a range in this way, the whole cranial form of this unique specimen can be further quantified by comparative coordinate-based methods such as GM or can be used for finite element modeling (FEM) explorations of hypotheses about the mechanics of early hominin feeding and diets.     

A geometric approach to cranial sexual dimorphism in the orang-utan

Adult craniofacial morphology is quantified and compared using Euclidean distance matrix analysis (EDMA), a three-dimensional morphometric method for the comparison of forms, which localizes form differences between comparative groups. Results indicate that the number and magnitude of differences between male and female crania are striking. The face, basicranium and neurocranium exhibit the most dimorphism, while the palate shows the least. Significant differences also exist between young adult and fully adult individuals, especially males, supporting the delayed onset of sexual maturity and secondary sex characteristics in males. As one of the many new morphometric techniques available, EDMA was useful for identifying local form difference and provides insights into the understanding of sexual dimorphism in this species beyond that obtained from traditional statistical methods based on linear caliper measurements.     

Technical note: Quantification of neurocranial shape variation using the shortest paths connecting pairs of anatomical landmarks

Three‐dimensional geometric morphometric techniques have been widely used in quantitative comparisons of craniofacial morphology in humans and nonhuman primates. However, few anatomical landmarks can actually be defined on the neurocranium. In this study, an alternative method is proposed for defining semi‐landmarks on neurocranial surfaces for use in detailed analysis of cranial shape. Specifically, midsagittal, nuchal, and temporal lines were approximated using Bezier curves and equally spaced points along each of the curves were defined as semi‐landmarks. The shortest paths connecting pairs of anatomical landmarks as well as semi‐landmarks were then calculated in order to represent the surface morphology between landmarks using equally spaced points along the paths. To evaluate the efficacy of this method, the previously outlined technique was used in morphological analysis of sexual dimorphism in modern Japanese crania. The study sample comprised 22 specimens that were used to generate 110 anatomical semi‐landmarks, which were used in geometric morphometric analysis. Although variations due to sexual dimorphism in human crania are very small, differences could be identified using the proposed landmark placement, which demonstrated the efficacy of the proposed method. Am J Phys Anthropol 151:658–666, 2013. © 2013 Wiley Periodicals, Inc.     

Palatal and dental arch morphology in Down syndrome

The analysis of palatal vault morphology and maxillary dental arch shape was carried out in the sample of 42 Down syndrome (DS) patients with trisomy 21. The data were compared to those of healthy controls from the same population matched for age and sex. Palatal morphology and upper dental arch shape were studied on hard plaster casts of the patients and controls. No sexual dimorphism in palatal and dental arch shape was observed in DS and controls. Normal palatal shape was more frequent in controls than in DS subjects (52.38% vs. 28.57%; p < 0.05). DS patients displayed significantly higher frequency of shelf-like or "stair palate" (38.1%) than controls (11.9%) (p < 0.02). The younger age group (3-14 year) showed much higher frequency of "stair palate" than controls (26.19% vs. 2.38%; c2 = 9.72; p = 0.003). The older group of DS patients did not show increased frequency of such shape of the palatal vault. There was no significant difference in dental arch shape between DS patients and controls. High frequency of shelf-like palate in DS subjects is decreasing by age. The obtained results indicate that palatal vault morphology is subjected to the age related changes. These changes can be attributed to the growth of caraniofacial structures and increased tonus of tongue and other orofacial muscles.     

Growth patterns in the modern human skeleton

This study investigates cross sectional growth patterns in the human skeleton using a recent skeletal sample of known age and sex. Measurements were selected to reflect different functional regions of the cranium, mandible and post cranial skeleton, and growth is evaluated using a single phase Gompertz curve. Different parts of the skeleton vary in the proportion of adult size attained at birth and in their subsequent rate of attainment of adult size. The paper introduces a method for the objective and quantitative comparison of the growth of different samples, and is used in this instance to analyze sexual differences in the growth of the post cranial skeleton. The development of sexual dimorphism is evaluated in terms of differences in the rate and duration of male and female growth. Adult sexual dimorphism is generally lower in early growing variables than in later-growing variables. There is considerable diversity in the ontogenetic basis of sexual dimorphism in the human skeleton demonstrating that the development of sexual dimorphism within a species should not be regarded as a uniform phenomenon. Am J Phys Anthropol 105:57–72, 1998. © 1998 Wiley-Liss, Inc.     

Sexual dimorphism of skull shape in a lacertid lizard species (Podarcis spp., Dalmatolacerta sp., Dinarolacerta sp.) revealed by geometric morphometrics

Geometric morphometric techniques were used to examine allometric and non-allometric influences on sexual shape dimorphism (SShD) in the ventral cranium (skull base, palate and upper jaw) of four species of lacertid lizards (Podarcis muralis, Podarcis melisellensis, Dalmatolacerta oxycephala, Dinarolacerta mosorensis). These species differ in body shape, ecology and degree of phylogenetic relatedness. The structures of the ventral cranium that were studied are directly involved in the mechanics of feeding and are connected to the jaw musculature; these structures are potentially subject to both sexual and natural selection. Allometry accounted for a considerable degree of cranial shape variation between the sexes. Allometric shape changes between individuals with smaller cranium size and individuals with larger cranium size are mostly related to changes in the skull base showing pronounced negative allometry. The rostral part, however, either scaled isometrically or showed less pronounced negative allometry than the skull base. Non-allometric intersexual shape variation predominantly involved changes related to the jaw adductor muscle chamber, i.e., changes that are associated with biomechanically relevant traits of the jaw system in females and males. Both allometric and non-allometric shape changes appeared to be species-specific. Our results indicate that natural and sexual selection may be involved in the evolution of SShD.     

Sexual dimorphism in the skull geometry of newt species of <Emphasis Type="Italic">Ichthyosaura,Triturus</Emphasis> and <Emphasis Type="Italic">Lissotriton</Emphasis> (Salamandridae,Caudata, Amphibia)

In this study, we applied geometric morphometrics to explore variations in the level and pattern of sexual size dimorphism (SSD) and sexual shape dimorphism (SShD) of the ventral cranium in three different Modern Eurasian newt taxa (Ichthyosaura alpestris, Triturus species group and Lissotriton vulgaris). The ventral cranium is the part of the skull that is more directly related to foraging and feeding. Our results indicate that the level and pattern of sexual dimorphism in the ventral cranium differ among Modern Eurasian newt taxa. Regarding sexual dimorphism in skull size, Ichthyosaura alpestris and Triturus species show female-biased patterns (females are larger than males), whereas Lissotriton vulgaris appears to be non-dimorphic in skull size. In I. alpestris and Triturus species, SShD is mostly absent, whereas in L. vulgaris, SShD is more pronounced. A high level of variation between populations in both SSD and SShD indicates that local conditions may have a profound effect on the magnitude and direction of sexual dimorphism. The significant sexual differences in ventral cranium size and shape indicate possible subtle intersexual differences in ecological demands due to diet specialisation, in spite of similar general ecological settings.     

Use of ordinal categorical variables in skeletal assessment of sex from the cranium

In anthropological studies, visual indicators of sex are traditionally scored on an ordinal categorical scale. Logistic and probit regression models are commonly used statistical tools for the analysis of ordinal categorical data. These models provide unbiased estimates of the posterior probabilities of sex conditional on observed indicators, but they do so only under certain conditions. We suggest a more general method for sexing using a multivariate cumulative probit model and examine both single indicator and multivariate indicator models on a sample of 138 crania from a Late Mississippian site in middle Tennessee. The crania were scored for five common sex indicators: superciliary arch form, chin form, size of mastoid process, shape of the supraorbital margin, and nuchal cresting. Independent assessment of sex for each individual is based on pubic indicators. The traditional logistic regressions are cumbersome because of limitations imposed by missing data. The logistic regression correctly classified 66/74 males and 46/64 females, with an overall correct classification of 81%. The cumulative probit model classified 64/74 males correctly and 51/64 females correctly for an overall correct classification rate of 83%. Finally, we apply parameters estimated from the logit and probit models to find posterior probabilities of sex assignment for 296 additional crania for which pubic indicators were absent or ambiguous. Am J Phys Anthropol 107:97–112, 1998. © 1998 Wiley-Liss, Inc.     

Sexual dimorphism in the cranium of infant and juvenile organutans

The present study examines sexual dimorphism in the cranium of the immature orangutan. A series of 37 craniometric dimensions were measured on 56 immature crania. The total sample was divided into two subsamples: infants and juveniles. Univariate statistics and an analysis of variance were prepared for each subsample. Results indicate that the males and females in both subsamples are significantly different (p less than or equal to 0.05) for two measures of skull length. Eight additional dimensions from the infant category also appear to differ significantly (p less than or equal to 0.05) between the sexes.     

Variation in the cranium shape of wall lizards (Podarcis spp.): effects of phylogenetic constraints, allometric constraints and ecology

We used geometric morphometrics to explore the influence of phylogenetic and allometric constraints as well as ecology on variation in cranium shape in five species of monophyletic, morphologically similar Podarcis lizards (Podarcis erhardii, Podarcis melisellensis, Podarcis muralis, Podarcis sicula and Podarcis taurica). These species belong to different clades, they differ in their habitat preferences and can be classified into two distinct morphotypes: saxicolous and terrestrial. We found (i) no phylogenetic signal in cranium shape, (ii) diverging allometric slopes among species, and (iii) a significant effect of habitat on cranium shape. The saxicolous species (P. erhardii and P. muralis) had crania with elongated parietals, elongated cranium bases, shortened anterior parts of the dorsal cranium, reduced chambers of the jaw adductor muscles and larger subocular foramina. These cranial features are adaptations that compensate for a flattened cranium, dwelling on vertical surfaces and seeking refuge in crevices. The crania of the terrestrial species (P. melisellensis, P. sicula and P. taurica) tended to be more elongate and robust, with enlarged chambers of the jaw adductor muscle, reduced skull bases and shortened parietals. Terrestrial species exhibited more variation in cranium shape than saxicolous species. Our study suggests that shape variation in Podarcis sp. lizards is largely influenced by ecology, which likely affects species-specific patterns of static allometry.     

Effects of fronto-occipital artificial cranial vault modification on the cranial base and face.

Artificial reshaping of the cranial vault has been practiced by many human groups and provides a natural experiment in which the relationships of neurocranial, cranial base, and facial growth can be investigated. We test the hypothesis that fronto-occipital artificial reshaping of the neurocranial vault results in specific changes in the cranial base and face. Fronto-occipital reshaping results from the application of pads or a cradle board which constrains cranial vault growth, limiting growth between the frontal and occipital and allowing compensatory growth of the parietals in a mediolateral direction. Two skeletal series including both normal and artificially modified crania are analyzed, a prehistoric Peruvian Ancon sample (47 normal, 64 modified crania) and a Songish Indian sample from British Columbia (6 normal, 4 modified). Three-dimensional coordinates of 53 landmarks were measured with a diagraph and used to form 9 finite elements as a prelude to finite element scaling analysis. Finite element scaling was used to compare average normal and modified crania and the results were evaluated for statistical significance using a bootstrap test. Fronto-occipitally reshaped Ancon crania are significantly different from normal in the vault, cranial base, and face. The vault is compressed along an anterior-superior to posterior-inferior axis and expanded along a mediolateral axis in modified individuals. The cranial base is wider and shallower in the modified crania and the face is foreshortened and wider with the anterior orbital rim moving inferior and posterior towards the cranial base. The Songish crania display a different modification of the vault and face, indicating that important differences may exist in the morphological effects of fronto-occipital reshaping from one group to another.     

Sexual dimorphism and interspecific cranial form in two capuchin species: Cebus albifrons and C. apella

Ontogenetic patterns of sexual dimorphism and cranial form in two capuchin monkeys, Cebus albifrons and C. apella, are investigated by means of univariate, bivariate, and multivariate statistics. The analyses are based on 23 linear variables. Univariate analyses indicate that similar ontogenetic patterns of cranial sexual dimorphism are present; however, interspecific differences exist in timing. Ontogenetic scaling is present in both species' crania; however, it is more prevalent in C. albifrons. Several departures are present in cranial regions associated with orbital shape, the dental arcade, and the muscles of mastication. The latter two indicate that sexual differences in diet and/or foraging strategies may exist. Sexual selection is suggested as being the primary selective regime underlying the observed patterns of cranial sexual dimorphism in each species. Interspecific comparisons confirm that C. apella possesses a more dimorphic cranium than C. albifrons and that sexual dimorphism in C. apella begins earlier in development. Although interspecific ontogenetic scaling is present in some cranial variables, C. apella is not just a scaled-up version of C. albifrons. These sympatric congeners seem to be differentiated by variables related to the orbital region and the masticatory apparatus, as indicated by both departures from ontogenetic scaling and results of the discriminant function analysis. Ecological selection, rather than varying degrees of sexual selection, is likely to be responsible for this finding given that C. apella is known to consume hard-object foods. This is consistent with the predicted outcome of the competitive exclusion principle. Am J Phys Anthropol 104:487–511, 1997. © 1997 Wiley-Liss, Inc.