The ontogeny of sexual dimorphism in the facial skeleton of the African apes

This paper aims to test the contribution of ontogenetic scaling to sexual dimorphism of the facial skeleton in the African apes. Specifically, it addresses whether males and females of each species share a common postnatal ontogenetic shape trajectory for the facial skeleton. Where trajectories are found to differ, it is tested whether male and female trajectories: 1) diverge early, or 2) diverge later after sharing a common trajectory earlier in the postnatal period. Where ontogenetic shape trajectories are found to be shared, it is also tested whether males and females are ontogenetically scaled. This study uses geometric morphometric analyses of 28 landmarks from the facial skeletons of 137 G. g. gorilla (62 adults; 75 juveniles), 95 P. paniscus (34 adults; 61 juveniles), and 115 P. t. troglodytes (58 adults; 57 juveniles). On average, males and females share a common ontogenetic shape trajectory until around the eruption of the second permanent molars. In addition, for the same period, males and females in each species share a common ontogenetic scaling trajectory. After this period, males and females diverge both from each other and from the common juvenile ontogenetic shape and scaling trajectories within each species. Thus, the male and female facial skeleton shows ontogenetic scaling until around the point of the eruption of the second molar (i.e., around puberty and the development of secondary sexual characteristics), but subsequent sexual dimorphism occurs via divergent trajectories and not via ontogenetic scaling.     

Head shape allometry and proximate causes of head sexual dimorphism in Podarcis lizards: joining linear and geometric morphometrics

Podarcis bocagei and Podarcis carbonelli are two lacertid species endemic to the western Iberian Peninsula, and both show head size and shape sexual dimorphism. We studied immature and adult head sexual dimorphism and analysed ontogenetic trajectories of head traits with body and head size, aiming to shed light on the proximate mechanisms involved. Immatures were much less dimorphic than adults, but geometric morphometric techniques revealed that head shape sexual differences are already present at this stage. Males and females differed in allometry of all head characters with body size, with males showing a disproportionate increase of head size and dimensions. On the other hand, head dimensions and head shape changed with increasing head size following similar trends in both sexes, possibly indicating developmental restrictions. Consequently, adult sexual dimorphism for head characters in these species is the result of both shape differences in the immature stage and hypermetric growth of the head in relation to body size in males.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 111–124.     

Surface facial modelling and allometry in relation to sexual dimorphism

Sexual dimorphism is responsible for a substantial part of human facial variability, the study of which is essential for many scientific fields ranging from evolution to special biomedical topics. Our aim was to analyse the relationship between size variability and shape facial variability of sexual traits in the young adult Central European population and to construct average surface models of adult males and females. The method of geometric morphometrics allowed not only the identification of dimorphic traits, but also the evaluation of static allometry and the visualisation of sexual facial differences.Facial variability in the studied sample was characterised by a strong relationship between facial size and shape of sexual dimorphic traits. Large size of face was associated with facial elongation and vice versa. Regarding shape sexual dimorphic traits, a wide, vaulted and high forehead in combination with a narrow and gracile lower face were typical for females. Variability in shape dimorphic traits was smaller in females compared to males. For female classification, shape sexual dimorphic traits are more important, while for males the stronger association is with face size.Males generally had a closer inter-orbital distance and a deeper position of the eyes in relation to the facial plane, a larger and wider straight nose and nostrils, and more massive lower face. Using pseudo-colour maps to provide a detailed schematic representation of the geometrical differences between the sexes, we attempted to clarify the reasons underlying the development of such differences.     

Ontogeny of sexual size dimorphism in monitor lizards: males grow for a longer period, but not at a faster rate

Monitor lizards belong to the largest and the most sexually dimorphic lizards in terms of size, making this group an ideal model for studies analyzing ontogenetic causes of sexual dimorphism. Understanding of these ontogenetic factors is essential to the current discussion concerning patterns of sexual dimorphism in animals. We examined the ontogenetic trajectories of body weight and snout-vent length to analyze the emergence of sexual size dimorphism. Experimental animals were 22 males and 13 females of mangrove-dwelling monitors (Varanus indicus) hatched at the Prague Zoo. They were regularly weighed and measured up to the age of 33-40 months, and subsequently sexed by ultrasonographic imaging. The logistic growth equation was used to describe and analyze the observed growth patterns. Our results confirm considerable sexual size dimorphism in the mangrove monitor. The mean asymptotic body weight of males was nearly three times higher than that of females. As the body size of male and female hatchlings is almost equal, and the growth rate parameter (K) of the logistic growth equation as well as the absolute growth rate up to the age of 12 months do not differ between the sexes, size differences between fully grown males and females should be attributed to timing of the postnatal growth. Males continue to grow several months after they reach the age when the growth of females is already reduced. Therefore, the sexual size dimorphism emerges and sharply increases at this period.     

Ontogeny and diachronic changes in sexual dimorphism in the craniofacial skeleton of rhesus macaques from Cayo Santiago, Puerto Rico

Insight into the ontogeny of sexual dimorphism is important to our understanding of life history, ecology, and evolution in primates. This study applied a three-dimensional method, Euclidean Distance Matrix Analysis, to investigate sexual dimorphism and its diachronic changes in rhesus macaque (Macaca mulatta) skulls. Twenty-one landmarks in four functional areas of the craniofacial skeleton were digitized from macaques of known age and sex from the Cayo Santiago collections. Then, a series of mean form matrices, form difference matrices, and growth matrices were computed to demonstrate growth curves, rates and duration of growth, and sexual dimorphism within the neurocranium, basicranium, palate, and face. The inclusion of fully adult animals revealed a full profile of sexual dimorphism. Additionally, we demonstrate for the first time diachronic change in adult sexual dimorphism caused by extended growth in adult females. A quicker growth rate in males from ages 2 to 8 was offset by a longer duration of growth in adult females that resulted in diminished dimorphism between the ages of 8 and 15. Four functional areas showed different sex-specific growth patterns, and the rate and duration of growth in the anterior facial skeleton contributed most to the changing profiles of sexual dimorphism. The late maturation in size of the female facial skeleton corresponds to later and less complete fusion of facial sutures. The prolongation of growth in females is hypothesized to be an evolutionary response to high levels of intrasexual competition, as is found in other primate species such as common chimpanzees with similar colony structure and reproductive behavior. Further investigation is required to determine (1) if this phenomenon observed in craniofacial skeletons is linked to sexual dimorphism in body size, and (2) whether this diachronic change in sexual dimorphism is species specific. The changing profile of sexual dimorphism in adult rhesus macaques suggests caution in studying sexual dimorphism in fossil primate and human forms.     

中国石龙子个体发育过程中头部两性异型和食性的变化

许多动物呈现个体大小、局部形态特征 (头部大小 )和体色的两性异形[5,14 ,15,2 1,2 2 ] 。 Darwin[12 ] 认为两性谋求各自最大的繁殖利益导致了两性异形 ,因此两性异形是性选择压力作用的结果。自 Darwin以来 ,许多同行认为性选择压力和非性选择压力均能导致动物的两性异形 ,两种选择压力在不同的动物中所起的作用是不同的 [2～ 5,7,10 ,16,2 1～ 2 6] 。性选择压力导致的两性异形与繁殖成功率直接有关。非性选择压力导致的两性异形与繁殖成功率无关或无直接的关系 ,如两性寿命的差异 [13 ]、两性食性的分离 [6,2 1]和两性分配用于生长的…     

Ontogenetic approaches to sexual dimorphism in anthropoids

Studies of sexual dimorphism have traditionally focused on the static differences in size and shape between adult males and females. In this paper, I suggest that an investigation of the ontogenetic bases of sexual dimorphism can provide new insights and information unobtainable from studies concerned only with adult endpoints. While growth is often viewed as simply the developmental pathway utilized to attain final adult size and shape, we must recognize that it is the entire pattern of sex-differentiated growth, and not merely the adult endpoints, which is adaptive and the target of natural selection. The importance of an ontogenetic approach to the analysis of sexual dimorphism is also demonstrated by the fact that a given morphologicalresult (e.g., a certain degree of adult weight dimorphism) may be attained by very different developmentalprocesses, signalling selection for quite different factors. The need to analyze the ontogenetic bases of sexual dimorphism in size and shape has recently been recognized by Jarman, in his study of dimorphism in large terrestrial herbivores. Here I combine aspects of Jarman’s approach with those of allometry and heterochrony in an analysis of sexual dimorphism in selected anthropoid primates. It is demonstrated that although all dimorphic anthropoids appear to be characterized by somebimaturism, the degree varies significantly. Marked weight dimorphism in certain species is primarily produced by an increased differentiation of female and male growthrates, while in other species the primary change involves differences in thetime or duration of growth between the sexes. These variations are illustrated with anthropoid genera such asMiopithecus, Cercopithecus, Erythrocebus, Macaca, Papio, Pan, andGorilla. It is suggested that additional ontogenetic investigations of other anthropoids will help clarify some of the socioecological bases of this variation in the ways of attaining an adult dimorphic state. This will contribute to our understanding of the complex factors underlying and producing sexual dimorphism in primates and other mammals.     

山地麻蜥个体发育过程中头部两性异形和食性的变化

研究了山地麻蜥(Eremias brenchleyi)个体发育过程中头部两性异形和食性的变化．成体个体大小(SVL)无显著的两性差异,但雄体具有较大的头部(头长和头宽)．头部两性异形在孵出幼体就已存在,成体头部两性异形比幼体(包括孵出幼体)更为显著,雄性较大的头部与其头部随SVL的增长速率大于雌性有关．两性头部总体上随SVL呈异速增长,表现为个体发育过程中头长和头宽与SVL的线性回归方程斜率有显著的变化．孵出幼体有相对较大的头部,这种形态特征是胚胎优先保证生态学意义更为显著的头部生长的结果,有利于孵出幼体的早期生存和生长．相对头部大小在个体发育过程中有显著的变化．不同性别和大小的山地麻蜥摄入食物的种类及各种食物在摄入食物中所占的比例有一定程度的差别,食物生态位宽度和重叠度因此有一定的差别．然而,没有直接的证据表明头部两性异形能导致两性食物生态位的明显分离,并有利于减缓两性个体对食物资源的竞争。     

Shape,size, and maturity trajectories of the human ilium

Morphological traits of the ilium have consistently been more successful for juvenile sex determination than have techniques applied to other skeletal elements, however relatively little is known about the ontogeny and maturation of size and shape dimorphism in the ilium. We use a geometric morphometric approach to quantitatively separate the ontogeny of size and shape of the ilium, and analyze interpopulation differences in the onset, rate and patterning of sexual dimorphism. We captured the shape of three traits for a total of 191 ilia from Lisbon (Portugal) and London (UK) samples of known age and sex (0–17 years). Our results indicate that a) there is a clear dissociation between the ontogeny of size and shape in males and females, b) the ontogeny of size and shape are each defined by non‐linear trajectories that differ between the sexes, c) there are interpopulation differences in ontogenetic shape trajectories, which point to population‐specific patterning in the attainment of sexual dimorphism, and d) the rate of shape maturation and size maturation is typically higher for females than males. Male and female shape differences in the ilium are brought about by trajectory divergence. Differences in size and shape maturation between the sexes suggest that maturity may confound our ability to discriminate between the sexes by introducing variation not accounted for in age‐based groupings. The accuracy of sex determination methods using the ilium may be improved by the use of different traits for particular age groups, to capture the ontogenetic development of shape in both sexes. Am J Phys Anthropol 156:19–34, 2015 © 2014 Wiley Periodicals, Inc.     

The ontogeny of sexual dimorphism in the cranium of Bornean orang-utans (Pongo pygmaeus pygmaeus): II. Allometry and heterochrony

Based on a homogeneous sample of 212 individuals spanning all postnatal periods, we examine the ontogeny of cranial sexual dimorphism in Bornean orang-utans (Pongo pygmaeus pygmaeus) by means of allometric analysis and in terms of heterochrony. The bivariate growth allometries of 20 cranial dimensions against basicranial length yield two major patterns. Confirming the null hypothesis, strong ontogenetic scaling, where growth regressions of both sexes fall along a single ontogenetic continuum, and where shape differences between adult males and females result from the extension of relative growth in the smaller females to larger size in males, is found in 10 cases. Ontogenetic scaling is particularly strong in proportions of (1) the neurocranium directly associated with brain size, (2) the orbital region, and (3) the dental arcade. In terms of heterochrony such a pattern most likely is the result of a process termed "time hypermorphosis", i.e. an extension of the growth period in time in males. The second major pattern seen in the remaining 10 cases shows a departure from ontogenetic scaling, with males exhibiting a significantly steeper slope than females. Departures from ontogenetic scaling, where size and shape are dissociated with adult males being disproportionately larger than adult females, are found in proportions of cranial regions directly associated with secondary sexual character development: prognathism, canine size, and cheek pad area. In terms of heterochrony such a pattern most likely is the result of a process termed "acceleration", i.e. the rate of shape change is increased in males.     

The ontogeny of cranial sexual dimorphism in two old world monkeys:Macaca fascicularis (Cercopithecinae) andNasalis larvatus (Colobinae)

Allometric and heterochronic approaches to sexual dimorphism have contributed much to our understanding of the evolutionary morphology of the primate skull and dentition. To date, however, extensive studies of sexual dimorphism have been carried out only on the great apes and a few cercopithecine monkeys. To fill this gap, representative dimensions of the skull were collected among ontogenetic series of two dimorphic Old World monkeys:Macaca fascicularis (Cercopithecinae) andNasalis larvatus (Colobinae). The ontogeny of cranial sexual dimorphism was evaluated with least-squares bivariate regression, analysis of covariance (ANCOVA), and analysis of variance (ANOVA). Results indicate that within each species the sexes typically exhibit nonsignificant differences in ANCOVAs of ontogenetic trajectories, except for bivariate comparisons with bicanine breadth. AmongMacaca fascicularis, ANOVAs between males and females of common dental ages show that adult, and frequently subadult, males are significantly larger than females, i.e., sexual dimorphism develops via time and rate hypermorphosis (males primarily grow for a longer time period as well as faster). AmongNasalis larvatus, however, comparisons between males and females of common dental ages indicate that only adult males are significantly larger than females, i.e., sexual dimorphism develops primarily via time hypermorphosis (males grow for a longer time period). Within both species, females appear to exhibit an early growth spurt at dental age 2; that is, many cranial measures for females tend to be larger than those for males. Measures of the circumorbital region (e.g., browridge height), body weight, and bicanine breadth exhibit typically the highest sexual dimorphism ratios. The fact that postcanine toothrow length and neurocranial volume (less so inNasalis) demonstrate very low dimorphism ratios generally supports assertions that postnatal systemic growth (and associated selective pressures thereon) exerts a greater influence on facial, but not neural, dental, or orbital, development (Cochard, 1985, 1987; Shea, 1985a,b, 1986; Shea and Gomez, 1988; Sheaet al., 1990). Additional consideration of ontogenetic differences between species generally supports previous functional interpretations of subfamilial differences in cranial form related to agonistic displays in cercopithecine monkeys (Ravosa, 1990).     

Ontogeny of craniofacial sexual dimorphism in the orangutan (Pongo pygmaeus). I: face and palate

The orangutan is widely recognized as a highly dimorphic species. An ontogenetic approach to the study of sexual dimorphism can assist researchers in understanding both where and when these differences develop. In this study, 357 orangutans from Borneo were divided into five developmental stages representing infancy to mature adulthood. Three-dimensional (3D) coordinate data from 16 landmarks representing the face and palate were analyzed by means of a Euclidean distance matrix analysis (EDMA), a quantitative method for the comparison of forms. Three separate analyses (an age-specific static comparison of forms, a sex-specific analysis of growth trajectories, and an intersex comparison of patterns of relative growth) were carried out with the intent to describe the rate, timing, magnitude, and pattern of growth in the orangutan face and palate. The results indicate that generally males and females share a similar, but not identical, pattern of growth or local form change, but differ in growth rate, timing, and magnitude of difference. Dimorphism in the face and palate can be localized in infancy and traced throughout all age intervals. Orangutan females grow slightly faster than males from infancy to adolescence, at which time male growth exceeds female growth. Female growth ceases with the advent of adulthood, while male growth continues (i.e., both the number and magnitude of the dimorphic dimensions increase). Males and females are similar in facial dimensions and growth related to the orbits, upper face, and palate width. They maintain these similarities throughout development. However, they differ in facial and nasal height, palate length, snout projection, depth of the nasopharynx, and hafting of the face onto the skull. The face broadens and the zygomatic bone flares dramatically in adult males, corresponding to the development of cheek pads. While growth patterns are similar between the two sexes, they differ in the lateral orbit, snout projection, and hafting of the face onto the cranium. Adult dimorphism is the result of growth patterns experienced throughout life, and it is not equally expressed across the cranium. An understanding of patterns of dimorphism, along with the magnitude of difference, may be helpful for interpreting dimorphism in the fossil record.     

An ontogenetic perspective on the study of sexual dimorphism, phylogenetic variability, and allometry of the skull of European ground squirrel, Spermophilus citellus (Linnaeus, 1766)

Most studies of morphological variability in or among species are performed on adult specimens. However, it has been proven that knowledge of the patterns of size and shape changes and their covariation during ontogeny is of great value for the understanding of the processes that produce morphological variation. In this study, we investigated the patterns of sexual dimorphism, phylogenetic variability, and ontogenetic allometry in the Spermophilus citellus with geometric morphometrics applied to cross-sectional ontogenetic data of 189 skulls from three populations (originating from Burgenland, Banat, and Dojran) belonging to two phylogenetic lineages (the Northern and Southern). Our results indicate that sexual dimorphism in the ventral cranium of S. citellus is expressed only in skull size and becomes apparent just before or after the first hibernation because of accelerated growth in juvenile males. Sexes had the same pattern of ontogenetic allometry. Populations from Banat and Dojran, belonging to different phylogroups, were the most different in size but had the most similar adult skull shape. Phylogenetic relations among populations, therefore, did not reflect skull morphology, which is probably under a significant influence of ecological factors. Populations had parallel allometric trajectories, indicating that alterations in development probably occur prenatally. The species’ allometric relations during cranial growth showed characteristic nonlinear trajectories in the two northern populations, with accelerated shape changes in juveniles and continued but almost isometric growth in adults. The adult cranial shape was reached before sexual maturity of both sexes and adult size after sexual maturity. The majority of shape changes during growth are probably correlated with the shift from a liquid to a solid diet and to a lesser degree due to allometric scaling, which explained only 20 % of total shape variation. As expected, viscerocranial components grew with positive and neurocranial with negative allometry.     

Heterochrony and sexual dimorphism in the skull of the Liberian chimpanzee (Pan troglodytes verus)

Allometric methods and theory derived from principles of relative growth provide new and powerful approaches to an understanding of the nature and development of sexual dimorphism among living primates. The Frankfurt collection of Liberian chimpanzee skulls and mandibles provides a large skeletal sample from a single natural population of wild shot animals, including individuals of all ages and both sexes, and allows investigation of allometric and heterochronic patterns of sexual dimorphism. Univariate, bivariate, and multivariate analyses are utilized in this study in order to ascertain the ontogenetic nature of male-female differences in the skull of the Liberian chimpanzee. The results of univariate and multivariate analyses indicate that, while overall levels of sexual dimorphism in the chimpanzee skull are small, the greatest differences are in dimensions of the viscerocranium, while neurocranial dimensions and orbital size tend to be less dimorphic. Bivariate regressions of 21 cranial variables against basicranial length document positive allometry in many facial and mandibular dimensions, and isometry or negative allometry for most neurocranial dimensions. The data confirm previous work in chimpanzees and other anthropoid primates suggesting that males and females are “ontogenetically scaled” in most cranial traits. That is, males and females share the same cranial growth trajectories, although ending up at different points. Both rate and time hypermorphosis are suggested as underlying causes of ontogenetic scaling in the Liberian chimpanzee.     

Ontogeny of facial dimorphism and patterns of individual development within one human population

Based on a longitudinal study of radiographs of the Denver Growth Study, we investigated the morphological development of individual and gender differences in the anterior neurocranium, face, and basicranium. In total, 500 X-rays of 14 males and 14 females, each with 18 landmarks and semilandmarks, were digitized and analyzed using geometric morphometric methods. Sexual dimorphism in shape and form is already present at the earliest age stage included in the analysis. However, the nature of dimorphism changes with age. Four factors apper to contribute to cranial sexual dimorphism in human postnatal development: 1) initial, possibly prenatal, differences in shape; 2) differences in the association of size and shape; 3) male hypermorphosis; and 4) some degree of difference in the direction of male and female growth trajectories. Studying changes in individuals, we find a low correlation between newborn and adult morphology, while 3-year-olds already show a high correlation with their adult form. We conclude that the adult pattern of interindividual difference in facial form in a single human population is established within the first few years of life.     

Sexual Selection,Ontogenetic Acceleration,and Hypermorphosis Generates Male Trimorphism in Wellington Tree Weta

Strong sex-specific selection on traits common to both sexes typically results in sexual dimorphism. Here we find that Wellington tree weta (Hemideina crassidens) are sexually dimorphic in both head shape and size due to differential selection pressures on the sexes: males use their heads in male-male combat and feeding whereas females use theirs for feeding only. Remarkably, the sexes share a common ontogenetic trajectory with respect to head growth. Male head shape allometry is an extension of the female’s trajectory despite maturing two instars earlier, a feat achieved through ontogenetic acceleration and hypermorphosis. Strong sexual selection also favours the evolution of alternative reproductive strategies in which some males produce morphologically different weapons. Wild-caught male H. crassidens are trimorphic with regard to weapon size, a rare phenomenon in nature, and weapon shape is related to each morph’s putative mating strategy.     

Quantitative analysis of sexual dimorphism and sex ratio in Hyphydrus ovatus (Coleoptera: Dytiscidae)

Sexual dimorphism in size, shape, and mass relative to length, and sex ratios are quantified for populations of Hyphydrus ovatus. a dytiscid beetle Males of H ovatus are not only longer than females, but also significantly larger in elytron length, thorax width, head width, leg length, total width, total depth, and abdominal segment length Two local populations differ slightly but significantly in total depth and abdominal segment length, but sexual dimorphism in size is similar for the two populations Hyphydrus ovatus are also sexually dimorphic in shape, with males having relatively broader heads and thoraxes than females The two populations differed slightly but significantly in relative abdominal segment length, but as with size, sexual dimorphism in shape is similar for the two populations Males are relatively heavier than females, although the slope of the log mass vs log length relationship is the same for the two sexes Sex ratios in field samples vary significantly over the summer, with percent females declining from c 50% to c 15% Sex ratios are significantly below 50% females m two of five monthly samples and in the total pooled set of samples Sexual dimorphism in size, shape, and relative mass, combined with male-biased sex ratios suggest that larger size of male H ovatus is a product of sexual selection     

Allometry of the postnatal cranial ontogeny and sexual dimorphism in Otaria byronia (Otariidae)

We studied the cranial postnatal ontogeny of Otaria byronia in order to detect sexual dimorphism in allometric terms, analyzing the rate of growth of functional variables linked to specific capacities as bite and head movements. We used 20 linear measurements to estimate allometric growth applying bivariate and multivariate analyses in females and males separately. Males were also analyzed in two partitioned subsets considering non-adult and adult stages, when the dimorphism is accentuated in order to reach optimal performance for intra-sexual competition. In the comparison of the employed techniques, we detected an empirical relationship between our multivariate results and the ordinary least square bivariate analysis. The quantitative analyses revealed different ontogenetic trajectories between non-adult and adult males in most variables, suggesting that the adult skull is not a scaled version of subadult skull. For instance, variables related with longitudinal dimensions decreased their allometric coefficients when the adult stage was reached, whereas those related with breadth or vertical dimensions increased their values. In adult males this could indicate that skull breadth and height are more important than longitudinal growth, relative to overall skull size. Conversely, inter-sexual comparisons showed that females and non-adult males shared similar ontogenetic growth trends, including more allometric trends than did males along their own ontogenetic trajectory. In general, adult males exhibited higher allometric coefficients than non-adult males in variables associated with bite and sexual behavior, whereas in comparison to females the latter showed higher coefficients values in these variables. Such patterns indicate a complex mode of growth in males beyond the growth extension, and are in partial agreement with changes previously reported for this and other species in the family Otariidae.     

Patterns of cranial sexual dimorphism in certain groups of extant hominoids

This paper presents a study of patterns of cranial variation within and between extant hominoids. Particular attention is paid to the relationship between sexual dimorphisms and size differences between sexes. It emerges that shape contrasts between sexes are closely linked to size differences whilst variance dimorphism appears to be relatively independent of size effects. This study demonstrates that there are differences between the hominoids in their magnitudes and patterns of sexual shape contrasts. These types of differences are also found to exist between subgroups of modern humans. It is suggested that the differences which occur between hominoid groups in their patterns of sexual dimorphism are probably the result of a mixture of time and rate hypermorphoses (in males relative to females) acting upon different ontogenetic trajectories. The findings of this study suggest the need for caution in extrapolating from the sexual dimorphisms found in living hominoids to hypothesized dimorphisms in fossils.