Skull Traits Research Articles

Bending performance changes during prolonged canine eruption in saber-toothed carnivores: A case study of Smilodon fatalis.

The canine of saber-toothed predators represents one of the most specialized dental structures known. Hypotheses about the function of hypertrophied canines range from display and conspecific interaction, soft food processing, to active prey acquisition. Recent research on the ontogenetic timing of skull traits indicates the adult canine can take years to fully erupt, but the consequences of prolonged eruption on inferences of canine functional morphology are missing from current discourse and have not been quantified. Here I evaluate hypotheses about adult canine bending strength and stiffness, respectively, during eruption in the felid Smilodon fatalis. Simulated eruption sequences of three adult canines were generated from specimen models to assess shifting cross-sectional geometry properties, and bending strength and stiffness under laterally directed loads were estimated using finite element analysis. Consistent with beam theory expectations, S. fatalis canine cross-sectional geometry is optimized for increased bending strength with increased erupted height. However, canine cross-sectional geometry changes through eruption exaggerate rather than minimize lateral deflection. Spatial constraint for maximum root length from adjacent sensory structures in the maxilla and the recently identified universal power law are hypothesized to limit the growth capacity of canine anteroposterior length and, consequently, maintenance of bending stiffness through eruption. Instead, the joint presence of the deciduous and adult canines for >50% of the adult canine eruption period effectively increases canine mediolateral width and brings bending strength and stiffness estimates closer to theoretical optima. Similarly prolonged retention of deciduous canines in other sabertooths suggests dual-canine buttressing is a convergently evolved strategy to maximize bending strength and stiffness.

Morphometric study of sex differences and static variation in the skull of Indochinese ground squirrel, Menetes berdmorei (Rodentia: Sciuridae)

Sexual dimorphism, a common morphological phenomenon in rodents, has often been explained as the result of both sexual and natural selection. However, few studies have focused on detailed patterns of sexual dimorphism in squirrels. In this study, we investigated the patterns of sex differences and static variation in the skull of Indochinese ground squirrel (Menetes berdmorei) using linear morphometrics. A total of 24 adult skulls (15 males and 9 females) were measured, of which males showed slightly larger mean size in 19 measurements. Univariate analyses demonstrated significant differences between the sexes in few variables, while discriminant analysis indicated well distinctiveness in craniomandibular morphology. The coefficient of variation showed an inverse relationship with the mean values of skull traits. This trend might be caused by real biological phenomena, as previously reported in several studies. Although coefficient of variation tended to be larger in anterior part of the viscerocranium and smaller in posterior of the neurocranium, similar variability patterns were observed in most of the skull trails. These trends were also supported by the alternative index of the coefficient of variation and coefficients of bivariate allometry. Even though, existence of developmental factors is suggested by the patterns of variability, higher integration is denoted in major subdivisions of the skull. In conclusion, our results demonstrate a slight male-biased sexual size dimorphism in M. berdmorei. Besides, variability patterns might indicate higher morphological integration in major components of the skull.

Diet-specific responses of skull traits to aridity gradients in bovids and cervids

Abstract Feeding efficiency of mammalian herbivores is associated with skull traits known to differ between feeding guilds. As climate is known to affect the architecture and functional traits of plants, skull morphology may change as plant traits change along climate gradients. We tested whether skull traits of more than 70% of the extant bovid and cervid species are related to aridity, and whether these relationships differ across feeding guilds (browser, grazer, mixed feeder). We used muzzle width to represent food ingestion and masseteric fossa length to represent oral processing. For the models without phylogeny, both muzzle width and masseteric fossa length increased towards wetter climates for grazers, but not for mixed feeders or browsers. These patterns suggest that grazer diets may change more dramatically across aridity gradients than the other two groups, possibly linked to changes in both the architecture and toughness of grasses. In models accounting for phylogeny, no changes in either trait across aridity gradient were found, which appeared to be due to subfamily differentiation along the aridity gradient. Our results suggest that deeper insights into the evolution of herbivore skulls may be achieved by using quantified diet data to directly test plant trait effects on skull morphology.

Morphological variability decreases in populations living in less suitable environments and close to the range edges

AbstractAimGeographical range expansion depends on ecological and evolutionary processes that may hamper local adaptations in populations living at range edges by constraining phenotypic variability. This study investigates the spatial patterns of the intraspecific variability of skull traits throughout the geographical range of a marsupial from the Brazilian Atlantic Forest. We aimed to answer whether the distance from the range edge and the environmental suitability explain the geographical variation of morphological variability of the species.LocationAtlantic Forest, Brazil.TaxonMarmosops incanus (Didelphimorphia, Didelphidae).MethodsWe analysed adult specimens deposited in the main biological collections in southeastern Brazil. The morphological variability extent and integration within populations were characterised by 13 linear measures of the skull, using a multivariate approach. Environmental suitability for the species' occurrence was estimated by ecological niche models, using climate variables and vegetation productivity as predictors and three different modelling methods. Distance from the range edge was calculated based on the minimum linear distance between populations and the closest range limit. We fitted linear regressions and selected the best models that explained the spatial variation of morphological variability based on the Akaike information criterion.ResultsThe extent of morphological variability of M. incanus is positively correlated with morphological integration and increases with local environmental suitability and distance from the range edges. However, the relationship between morphological variability and environmental suitability depends on the niche modelling method.Main ConclusionsUnfavourable environmental conditions constrain morphological variability within populations of the Gray slender opossum and may hamper local adaptation in peripheral populations living in less suitable environments. In addition to environmental conditions, geographical location of populations also plays an important role in phenotypic variability among populations. We stress the boundary effect of the species range on local adaptation of peripheral populations and its possible consequences for the range expansion dynamics.

Statistical classification methods for estimating sex based on five skull traits: A nonmetric assessment using 3D CT models.

Five cranial nonmetric traits for sex estimation for sex estimation are classified by score according to geometry. The population of origin is one of the factors influencing cranial nonmetric traits. Moreover, among the five cranial traits, the robust traits for estimating sex varied across population. The aim of this study is to suggest the most useful method for sex estimation and demonstrate the need of a suitable method for each population. One-hundred thirty-five three-dimensional skull images from 21st century Korean autopsy cadavers were evaluated using the ordinal scoring system of five cranial nonmetric traits as outlined in Buikstra & Ubelaker (1994). All scores of each trait were analyzed by linear discriminant and decision tree analyses for sex estimation. The frequency of each trait was analyzed and compared to populations from other studies. The accuracy for both sexes was 88.1% by discriminant analysis and 90.4% by decision tree. The traits with the highest accuracy were the glabella and mastoid process in both discriminant analysis and decision tree. Sex estimation in modern Korean cadavers using the cranial nonmetric method was shown to be highly accurate by both discriminant analysis and decision tree. When comparing the pattern of frequency scores in this study with those of other populations, the pattern of trait scores for estimating sex was different for each population, even among populations in the same Asian region, which suggests the need for methods suited for specific populations.

An early bothremydid from the Arlington Archosaur Site of Texas

Four turtle taxa are previously documented from the Cenomanian Arlington Archosaur Site (AAS) of the Lewisville Formation (Woodbine Group) in Texas. Herein, we describe a new side-necked turtle (Pleurodira), Pleurochayah appalachius gen. et sp. nov., which is a basal member of the Bothremydidae. Pleurochayah appalachius gen. et sp. nov. shares synapomorphic characters with other bothremydids, including shared traits with Kurmademydini and Cearachelyini, but has a unique combination of skull and shell traits. The new taxon is significant because it is the oldest crown pleurodiran turtle from North America and Laurasia, predating bothremynines Algorachelus peregrinus and Paiutemys tibert from Europe and North America respectively. This discovery also documents the oldest evidence of dispersal of crown Pleurodira from Gondwana to Laurasia. Pleurochayah appalachius gen. et sp. nov. is compared to previously described fossil pleurodires, placed in a modified phylogenetic analysis of pelomedusoid turtles, and discussed in the context of pleurodiran distribution in the mid-Cretaceous. Its unique combination of characters demonstrates marine adaptation and dispersal capability among basal bothremydids.

Application of the Optimized Summed Score Attributes Method for Sex Estimation

The optimized summed scored attributes (OSSA) method was first developed for cranial ancestry estimation (Hefner & Ousley 2014). Tallman and Go (2018) adapted this method for sex estimation with the five skull traits described by Buikstra and Ubelaker (1994) and Walker (2008). Using an Asian sample, Tallman and Go (2018) achieved moderate accuracy rates (83.7% calibration; 81.9% validation) but also high sex bias (29.1% calibration; 34.5% validation), possibly due to lower levels of sexual dimorphism in Asian populations. To further explore this novel approach to sex estimation, the OSSA method was applied to a U.S. Black/African ancestry and White/European ancestry calibration sample (N = 700). Accuracy rates were 77.4% in Black individuals and 77.2% in White individuals. Despite generally higher levels of sexual dimorphism in these groups, a high sex bias still occurred (15.4% Black individuals; –20.5% White individuals) using OSSA. The method was tested in a separate validation sample (N = 200) with accuracy of 78.0% in Black individuals (8.0% sex bias) and 70.0% in White individuals (–56.0% sex bias). When these same traits were tested with Walker’s (2008) logistic regression and in the MorphoPASSE Program (Klales 2018) using random forest modeling, accuracy rates varied ,with OSSA (77.3% correct), performing slightly better than Walker’s (2008) method (75.6% correct) but worse than MorphoPASSE (85.3% correct). The higher accuracy and lower sex bias in MorphoPASSE suggests that the Walker (2008) traits can be used to accurately estimate sex with statistical approaches more appropriate and robust than OSSA.

Craniometric Variability of the Common Shrew (Sorex araneus, Eulipotyphla) in the Northeastern Part of European Russia: Effects of Various Factors

Craniometric variability of the common shrew has been studied on 613 skulls of young (first summer of life) individuals from ten localities in the northeastern part of European Russia, i.e., Komi Republic and Nenets Autonomous Okrug. We have compared 16 skull traits. The impact of various factors on cranial variability of the species is discussed. We found significant interpopulation variability in the skull size. The morphological distances (Mahalanobis distances) between samples within a race were often greater than those between samples of different races. Several skull traits were found specific to some races. Both latitude and elevation were shown to affect the interpopulation variability significantly. A decrease in the size of skulls was revealed towards the north versus an increase with altitude. Estimation of the contribution of a certain factor was complicated by the joint effect of various factors in various combinations.

An exceptional neurovascular system in abelisaurid theropod skull: New evidence from Skorpiovenator bustingorryi.

Abelisaurids were one of the most successful theropod dinosaurs during Cretaceous times. They are featured by numerous derived skull traits, such as heavily ornamented bones, short and tall snout, and a strongly thickened cranial roof. Furthermore, nasals are distinctive on having two distinct nasal patterns: strongly transversely convex and heavily sculptured (e.g., Carnotaurus), and transversely concave, with marked bilateral crests and poorly sculptured surfaces (e.g., Rugops). Independently of the pattern, some abelisaurid nasals (e.g., Rugops) show a distinctive row of large foramina on the dorsal surface, which were in general associated to skin structures (scales). Skorpiovenator bustingorryi is a derived abelisaurid coming from the upper Cretaceous beds of northwestern Patagonia, represented by an almost complete skeleton including a well-preserved skull. Particularly, the skull of Skorpiovenator shows nasal bones characterized by being transversely concave, rimmed by lateral crests and with a conspicuous row of foramina on the dorsal surface. But more interesting is that the skull roof also exhibits a row of large foramina that seem to be continuous with the previous nasal foramina. CT scans made on the skull corroborates a novel feature within theropods: the nasal foramina on the external surface are linked to an internal canal that runs across the nasal bones. We compared this feature with CT scans of Carnotaurus and revealed that it also possess an internal system as in Skorpiovenator, but being notably smaller. The symmetry and disposition of the foramina in the nasal and skull roof bones of Skorpiovenator would indicate a neurovascular correlate (i.e., blood vessels and nerves), probably to the lateral nasal and supraorbital vessels and the trigeminal nerve. The biological significance of such neurovascular system can be conjectured from several hypotheses. A possible one involves an enhanced blood volume in these bones linked to a zone of thermal exchange, which may help avoid overheat of encephalic tissues. Another plausible hypothesis takes into account the presence of display skin structures in which blood volume nourished the mineralized skin, which would have a role in intraspecific communication. However, other more speculative explanations should not be discarded such as a correlation with integumentary sensory organs.

Skull morphology diverges between urban and rural populations of red foxes mirroring patterns of domestication and macroevolution.

Human activity is drastically altering the habitat use of natural populations. This has been documented as a driver of phenotypic divergence in a number of wild animal populations. Here, we show that urban and rural populations of red foxes (Vulpes vulpes) from London and surrounding boroughs are divergent in skull traits. These changes are primarily found to be involved with snout length, with urban individuals tending to have shorter and wider muzzles relative to rural individuals, smaller braincases and reduced sexual dimorphism. Changes were widespread and related to muscle attachment sites and thus are likely driven by differing biomechanical demands of feeding or cognition between habitats. Through extensive sampling of the genus Vulpes, we found no support for phylogenetic effects on skull morphology, but patterns of divergence found between urban and rural habitats in V. vulpes quantitatively aligned with macroevolutionary divergence between species. The patterns of skull divergence between urban and rural habitats matched the description of morphological changes that can occur during domestication. Specifically, urban populations of foxes show variation consistent with ‘domestication syndrome’. Therefore, we suggest that occurrences of phenotypic divergence in relation to human activity, while interesting themselves, also have the potential to inform us of the conditions and mechanisms that could initiate domestication. Finally, this also suggests that patterns of domestication may be developmentally biased towards larger patterns of interspecific divergence.

Taxonomic revision of the pampas catLeopardus colocolacomplex (Carnivora: Felidae): an integrative approach

AbstractThe pampas cat Leopardus colocola has been subject to conflicting classifications over the years. Currently, one polytypic species with seven subspecies is recognized, but integrative taxonomic study for this debated group has never been done. Here, we combine the broadest morphological coverage of the pampas cat to date with molecular data and ecological niche models to clarify its species composition and test the validity of recently proposed subspecies. The multiple lines of evidence derived from morphology, molecular, biogeography and climatic niche datasets converged on the recognition of five monotypic species: L. braccatus, L. colocola, L. garleppi (including thomasi, budini, steinbachi, crespoi and wolffsohni as synonyms), L. munoai and L. pajeros (including crucina as synonym). These five species are morphologically diagnosable based on skin and skull traits, have evolved in distinct climatic niche spaces and were recovered in molecular species delimitation. Contrary to previous taxonomic arrangements, we do not recognize subspecies in pampas cats. To objectively define the two most controversial species, we designate neotypes for L. colocola and L. pajeros. The diversification of pampas cats is associated with Middle Pleistocene glaciations, but additional genetic samples from the central Andean region are still needed to conclusively reconstruct its evolutionary history.

Integrative taxonomy of the southernmost tucu-tucus in the world: differentiation of the nominal forms associated with Ctenomys magellanicus Bennett, 1836 (Rodentia, Hystricomorpha, Ctenomyidae)

We reviewed the alpha taxonomy of the genus Ctenomys Blainville, 1826 in southernmost South America, with emphasis on those nominal forms previously associated with C. magellanicus Bennett, 1836. We integrate distinct lines of evidence, including variation of mtDNA sequences, and the assessment of quantitative and qualitative traits of skins and skulls; when available, karyotypic data was also considered. Phylogenetic analysis of molecular markers shows low levels of divergence among specimens from southern South American mainland and the island of Tierra del Fuego (ca. 0.4%). This evidence plus the results of the multivariate analysis of metric data suggest that the nominal forms C. colburni J. A. Allen, 1903, C. fueginus Philippi, 1880, C. osgoodi J. A. Allen, 1905, C. m. dicki Osgood, 1943, and C. m. obscurus Texera, 1975 are subjective junior synonyms of C. magellanicus. In addition, we reviewed the status of C. fodax Thomas, 1910, a nominal form that have been alternatively considered as a valid species or related to C. magellanicus by previous researchers. Based on quantitative and qualitative morphological traits, we preliminarily regard C. fodax at the species level while citing it for the first time to Chile.

Variation in non-metrical skull traits of polar bears (Ursus maritimus) and relationships across East Greenland and adjacent subpopulations (1830–2013)

Knowledge of subpopulation identity including substructure is a prerequisite for sound management of polar bears (Ursus maritimus). It is not known whether the present catch of polar bears in the East Greenland subpopulation (EG) is sustainable. We used the Mean Measure of Divergence (MMD) to examine geographical variation in non-metrical traits from 1414 polar bear (Ursus maritimus) skulls collected in East Greenland (EG), Svalbard (SVA), Franz Josef Land (FJL), Davis Strait (DS), Baffin Bay (BB), and Kane Basin (KB), between 1830 and 2013. We focused on East Greenland with the goal of examining substructuring in the subpopulation. We did not find significant differences among samples across four areas of the EG subpopulation (i.e., offshore Fram Strait, NE, SE, and SW Greenland) using data from 1830 to 1983. Our analyses did not lend support to substructuring. However, we draw our conclusions with caution because skulls were sampled over a long time period and had low power due to small sample sizes. Also, comparisons were limited to pre-1980s skulls. The decrease in sea ice in EG since the 1990s due to climate change may have led to substructuring not detected with MMD. This study contributes to the current efforts by Greenland authorities to quantify connectivity of polar bears between southeast and northeast Greenland which is important information for the evaluation of the sustainability of the catch of bears from the EG subpopulation.

Morphological adaptations for relatively larger brains in hummingbird skulls.

A common allometric pattern called Haller's Rule states that small species have relatively larger brains and eyes than larger species of the same taxonomic group. This pattern imposes drastic structural changes and energetic costs on small species to produce and maintain a disproportionate amount of nervous tissue. Indeed, several studies have shown the significant metabolic costs of having relatively larger brains; however, little is known about the structural constraints and adaptations required for housing these relatively larger brains and eyes. Because hummingbirds include the smallest birds, they are ideal for exploring how small species evolve morphological adaptations for housing relatively larger brain and eyes. We here present results from a comparative study of hummingbirds and show that the smallest species have the lowest levels of ossification, the most compact braincases, and relatively larger eye sockets, but lower eye/head proportion, than larger species. In contrast to Passerines, skull ossification in hummingbirds correlates with body and brain size but not with age. Correlation of these skull traits with body size might represent adaptations to facilitate housing relatively larger brain and eyes, rather than just heterochronic effects related to change in body size. These structural changes in skull traits allow small animals to accommodate disproportionately larger brains and eyes without further increasing overall head size.

Geographic variation in quantitative skull traits in the genus Myoprocta Thomas, 1903 (Rodentia, Dasyproctidae) and its taxonomic implications

Abstract The genus Myoprocta Thomas, 1903 includes two living species of medium-sized caviomorph rodents of the family Dasyproctidae, the red acouchi, Myoprocta acouchy (Erxleben 1777), and the green acouchi, Myoprocta pratti Pocock 1913. Whereas some recent revisionary work has considered both species to be allopatrically distributed, other reports suggest that both taxa co-occur in eastern Colombia. In this contribution, I revaluate some qualitative and quantitative skull traits within Myoprocta to clarify its taxonomy and distribution. Multivariate analyses of quantitative skull characters support the distinction between M. acouchy and M. pratti, contradicting the findings of some previous authors. Based on these results and the examination of ~100 skins, I concur with the hypothesis that the two species are allopatrically distributed.

Geographic variation in quantitative skull traits and systematic of southern populations of the leaf-eared mice of the Phyllotis xanthopygus complex (Cricetidae, Phyllotini) in southern South America.

The leaf-eared mice of the genus Phyllotis (Cricetidae, Phyllotini) encompasses at least 20 species of medium-sized Neotropical rodents mostly distributed throughout the Andean region. Its limits and contents were reviewed by several authors, based both on morphological and molecular data. However, no integrative approaches were conducted based on large samples of individuals with a wide geographical coverage. The purposes of this paper are: (i) to evaluate species limits; and (ii) to test the congruence between molecular and quantitative morphological evidences within the Phyllotis xanthopygus complex in southern South America. Our results questioned the specific status of P. bonariensis, a geographically isolated form that was either considered as a valid species or as a synonym of P. xanthopygus. Quantitative morphological (size and shape of the skull) and molecular data linked P. bonariensis with populations from central Argentina traditionally referred as P. xanthopygus vaccarum. Individuals belonging to populations from southern Argentina and Chile (P. x. xanthopygus) were remarkably homogeneous in their skull morphology, showing a subtle to non-existent differentiation from those of north-central and west-central Argentina referred to P. x. vaccarum. We found some incongruence between groups inferred from morphological (this work) and mitochondrial DNA results of previous studies. This is the case of the north-central and west-central populations, where morphological traits do not show the strong differentiation detected by molecular characters. Our results highlight the need for integrative taxonomic studies, not only to delimitate taxonomic units but also for a better and more comprehensive understanding of population variability and differentiation.

Diferente desarrollo cefálico según tipo de conejo

Como alometría se entiende el crecimiento relativo de una estructura biológica respecto a otra(s) o al organismo total y da cuenta de los cambios de conformación que derivan de la modificación de tamaño. Un caso particular es cuando la velocidad de crecimiento es la misma entre los caracteres en estudio, lo cual recibe el nombre de isometría. A fin de estudiar este fenómeno en el conejo doméstico, se colectó un total de 71 cadáveres frescos de conejos, de diferente edad, correspondientes a animales destetados, y se obtuvo por descarnado el cráneo de cada uno. De ellos, 59 correspondían al tipo de compañía (tipos “toys” y “beliers”) y 12 al tipo carnicero (californiano/neozelandés). Se captó una imagen digital, en la cara lateral, de cada cráneo, sobre la que posteriormente se situaron 12 hitos anatómicos, analizados mediante métodos de morfometría geométrica. Los conejos de carne presentaron un comportamiento claramente isométrico, mientras que los de compañía, y a pesar de que muchos ya eran adultos, este comportamiento era alométrico. Nos encontramos, pues, ante un caso de gerontomorfia en los conejos de carne —un desarrollo precoz— y una pedomorfia en los de compañía —un retardo en su crecimiento, puesto que, aunque adultos, siguen presentando una cara corta y plana, y un cráneo proporcionalmente grande, caracteres típicamente juveniles—. Para los primeros un desarrollo lo más precoz posible y para los segundos una retención de los caracteres juveniles; en ambos tipos, ejemplo de heterocronías de desarrollo.

Evolution of morphological integration in the skull of Carnivora (Mammalia): Changes in Canidae lead to increased evolutionary potential of facial traits.

Morphological integration refers to the fact that different phenotypic traits of organisms are not fully independent from each other, and tend to covary to different degrees. The covariation among traits is thought to reflect properties of the species' genetic architecture and thus can have an impact on evolutionary responses. Furthermore, if morphological integration changes along the history of a group, inferences of past selection regimes might be problematic. Here, we evaluated the stability and evolution of the morphological integration of skull traits in Carnivora by using evolutionary simulations and phylogenetic comparative methods. Our results show that carnivoran species are able to respond to natural selection in a very similar way. Our comparative analyses show that the phylogenetic signal for pattern of integration is lower than that observed for morphology (trait averages), and that integration was stable throughout the evolution of the group. That notwithstanding, Canidae differed from other families by having higher integration, evolvability, flexibility, and allometric coefficients on the facial region. These changes might have allowed canids to rapidly adapt to different food sources, helping to explain not only the phenotypic diversification of the family, but also why humans were able to generate such a great diversity of dog breeds through artificial selection.

Trait‐specific processes of convergence and conservatism shape ecomorphological evolution in ground‐dwelling squirrels

Our understanding of mechanisms operating over deep timescales to shape phenotypic diversity often hinges on linking variation in one or few trait(s) to specific evolutionary processes. When distinct processes are capable of similar phenotypic signatures, however, identifying these drivers is difficult. We explored ecomorphological evolution across a radiation of ground-dwelling squirrels whose history includes convergence and constraint, two processes that can yield similar signatures of standing phenotypic diversity. Using four ecologically relevant trait datasets (body size, cranial, mandibular, and molariform tooth shape), we compared and contrasted variation, covariation, and disparity patterns in a new phylogenetic framework. Strong correlations existed between body size and two skull traits (allometry) and among skull traits themselves (integration). Inferred evolutionary modes were also concordant across traits (Ornstein-Uhlenbeck with two adaptive regimes). However, despite these broad similarities, we found divergent dynamics on the macroevolutionary landscape, with phenotypic disparity being differentially shaped by convergence and conservatism. Such among-trait heterogeneity in process (but not always pattern) reiterates the mosaic nature of morphological evolution, and suggests ground squirrel evolution is poorly captured by single process descriptors. Our results also highlight how use of single traits can bias macroevolutionary inference, affirming the importance of broader trait-bases in understanding phenotypic evolutionary dynamics.

Sex determination in forensic identification, a review.

Forensic odontology is the application of dental principles to legal issues. It is an investigative aspect of dentistry that analyzes dental evidence for human identification. Sex determination is a subdivision of forensic odontology, and it is important especially when information relating to the deceased is unavailable. Sex determination becomes the first priority in the process of identification of a person by a forensic investigator in the case of mishaps, chemical and nuclear bomb explosions, natural disasters, crime investigations, and ethnic studies. Determination of sex/gender using skeletal remains presents a great problem to forensic experts, especially when only fragments of body are recovered. Forensic odontologist can assist other experts to determine the sex of the remains using teeth and skull traits. Various features of teeth such as morphology, crown size, and root length are characteristics for male and female sexes. There are also differences in the skull pattern and skull traits of two sexes. These will help forensic odontologists to identify the sex of the remains. The library dissertation contents and several articles and books were electronically searched in Google using the keywords “sex determination,” “forensic dentistry,” “sex determination in forensic dentistry.” The contents were screened between 1950 and 2015 by going through the title and abstracts and full-text reading. The purpose of this article is to familiarize the different methods of sex determination.