SEX DETERMINATION OF THE CALIFORNIA SEA LION (ZALOPHUS CALIFORNIANUS CALIFORNIANUS) FROM CANINE TEETH

Size of canine teeth from California sea lion ( Zalophus californianus californianus ) carcasses is shown to be useful in determining the sex of animals which have missing genitalia or which are otherwise of unknown sex. A total of 267 canine teeth from carcasses of 68 males and 43 females were measured along five axes. Of root and crown measurements of upper and lower canines, males and females overlapped only in root thickness of upper canines. A multivariate ANOVA showed a significant difference in the size of canines between upper and lower canines, and between males and females. Stepwise discriminant analysis produced discriminant functions for upper and lower canines for determining sex of unknown-sexed California sea lions. A separate set of canine teeth from 39 male and 49 female California sea lions was correctly classified without prior knowledge of sex by visual inspection and by the two discriminant functions.     

Sexual dimorphism of tooth size in anthropoids

We have examined the size of the canine and postcanine teeth of cebid and catarrhine primates in relation to each other, to jaw size and to body weight. We have found that the canine size of males is large enough to be limited by jaw shape and size. A large contribution of P4 to the postcanine row is associated with smaller canines in males. Neither factor seems to limit canine size in females. The females of a small number of species possess enlarged canines. Much of the variation of the postcanine row can be described by the ratio of the (nominal) crown areas of M1 to M3. This ratio is monomorphic which conforms with the general lack of dietary dimorphism in primates. A brief discussion of the evolution of canine size is offered with a new suggestion to account for canine reduction in male hominids.     

An analysis of canine size and jaw shape in some Old and New World non-human primates

An analysis of the relationship between the height of canine teeth, the length of the jaw and the height of the jaw joint above the occlusal plane was undertaken in catarrhine primates and some cebids. An inverse relationship was found in males between the angle
the jaw must be opened to clear the canine teeth and the height of the jaw joint above the occlusal plane, divided by the length of the lower jaw. A theoretical model is presented which can account for this phenomenon and which presumes selection pressure for alignment of the canine teeth when in use. In females, the angle the jaw must be opened to clear
the canine teeth was in most cases very small though in certain species elongated canines
were found.     

Allometric relations of teeth and jaws in man

Static adult intraspecific allometry of jaws and teeth was investigated in a sample of 100 Negro crania. The relations between tooth area, postcanine surface, incisor surface, and four viscerocranial measures were examined separately for males and females. Our results indicate a marked lack of morphological integration between P-sets within the orofacial subregion and a similar lack of correspondence between jaw size and tooth size. Allometric analyses indicate that mandibular length scales negatively allometric to maxilloalveolar length and to bigonial width, that canine base area scales positively to upper and lower jaw length, and that all the other teeth scale negatively to jaw length. The postcanine surface area was found to be negatively allometric to the canine base area, which in turn scaled isometrically to incisor surface. Hence, any lengthening of the mandible will tend to be associated with a relative shortening of the maxilla, with relatively larger canines and a relative reduction of the cheek teeth.     

Static intraspecific allometry of jaws and teeth in Cercopithecus aethiops

Adult static intraspecific allometry of jaw size and tooth area was evaluated in a sample of 100 Cercopithecus aethiops crania (50 male, 50 female). Tooth areas were calculated from mesiodistal and buccolingual measurements of all the teeth in both arcades and were scaled to four viscero-cranial measurements: bimaxillary breadth, maxillo-alveolar length, mandibular length and bigonial width. Allometric coefficients calculated for jaw dimensions alone indicate tighter viscerocranial integration in females than in males. A finding of note was that half of the variation in maxillo-alveolar length may be accounted for by variation in mandibular length: females are isometric, males negatively allometric.
A similar degree of allometric mosaicism was found when maxillary incisor size was scaled to maxillary length and width. In females, the relationship was negatively allometric, whilst incisor size in males was found to be unrelated to either. Negative allometry characterized the relationship of canine base area to jaw length in both sexes, with males additionally being positively allometric to mandibular width.
The scaling of postcanine tooth areas to jaw length was characterized by a dichotomous pattern: males showed significant mandibular integration whilst females showed only significant maxillary integration. Compensatory tooth size interaction between maxillary canine base area and the summed incisor and postcanine areas was suggested by the significant negative allometric relation between them.     

Static intraspecific maxillofacial allometry in the chacma baboon

Adult static intraspecific allometry of jaw size and tooth area was evaluated in a sample of 104 Papio ursinus crania (52 male, 52 female). Tooth areas were calculated from mesiodistal and buccolingual measurements of all the teeth in both arcades and were scaled to four viscerocranial measurements: bimaxillary width, maxillo-alveolar length, mandibular length and bigonial width. Craniodental allometric analyses indicate that larger animals will tend to have proportionately shorter and narrower lower jaws. From the log-transformed interspecific analyses between P. ursinus and C. aethiops we conclude that males and females within each species share a common exponential value for jaw length. Hence increased sexual dimorphism for muzzle length in P. ursinus is attributable to increased divergence between the male and female slopes. Post-canine area was found to be significantly correlated to maxillary length and to canine size only in females, with exponential values similar to those reported for the same bivariate regressions in C. aethiops. A hypothesis of nutritional equivalence is advanced to account for these observations. Canine base area and the area of P3 were the only tooth areas that scaled in a positively allometric fashion to jaw size--but only in males. Hence the existence of a canine complex is confirmed in the male Chacma baboon, the size of which is related to jaw length.     

Canine size, shape, and bending strength in primates and carnivores

Anthropoid primates are well known for their highly sexually dimorphic canine teeth, with males possessing canines that are up to 400% taller than those of females. Primate canine dimorphism has been extensively documented, with a consensus that large male primate canines serve as weapons for intrasexual competition, and some evidence that large female canines in some species may likewise function as weapons. However, apart from speculation that very tall male canines may be relatively weak and that seed predators have strong canines, the functional significance of primate canine shape has not been explored. Because carnivore canine shape and size are associated with killing style, this group provides a useful comparative baseline for primates. We evaluate primate maxillary canine tooth size, shape and relative bending strength against body size, skull size, and behavioral and demographic measures of male competition and sexual selection, and compare them to those of carnivores. We demonstrate that, relative to skull length and body mass, primate male canines are on average as large as or larger than those of similar sized carnivores. The range of primate female canine sizes embraces that of carnivores. Male and female primate canines are generally as strong as or stronger than those of carnivores. Although we find that seed-eating primates have relatively strong canines, we find no clear relationship between male primate canine strength and demographic or behavioral estimates of male competition or sexual selection, in spite of a strong relationship between these measures and canine crown height. This suggests either that most primate canines are selected to be very strong regardless of variation in behavior, or that primate canine shape is inherently strong enough to accommodate changes in crown height without compromising canine function.     

Sexual dimorphism in canine shape among extant great apes

There have been numerous attempts to sex fossil specimens using the canine dentition. Whether focused on canine size or canine shape, most of these efforts share two deficiencies: lack of quantification of male-female differences in the adopted criteria and a failure to adequately explore among extant species the discriminatory power of these criteria. Here, canine shape indices relating to relative canine height, upper canine root/crown proportionality, and relative length of the lower canine mesial ridge were calculated for males and females of all species and subspecies of extant great apes and two species of gibbons. The accuracy of these indices for identifying the sex of the extant ape specimens was investigated through discriminant analysis and the use of bivariate plots of the two upper and two lower canine indices. The indices were found to be highly accurate in identifying the sex of great ape individuals, not only in single-species and subspecies samples but in mixed-species samples as well; assignment error rates were mostly between 0 and 4%. Accuracy was lowest in Pan (error rates as high as 15%) and highest in Pongo (one error). In most cases, error rates were lower in the upper canines. The effectiveness of these shape indices for sexing might be related to the degree of absolute canine size dimorphism; the indices did not effectively segregate males and females among minimally canine-dimorphic gibbons. The mixed-species results reveal that same-sex index values are remarkably concordant across great ape species, as are the patterns of spatial segregation of males and females in the bivariate plots. Results suggest that, while the indices can be used with some confidence to sex individual fossil specimens, their greatest utility will be for identifying the sex of groups of canines united by size and morphology. © 1995 Wiley-Liss, Inc.     

Intrasexual selection and phylogenetic constraints in the evolution of sexual canine dimorphism in strepsirhine primates

The goals of this study were to analyze the origin and function of sex differences in the size of canine teeth among Malagasy lemurs and other strepsirhine primates. These analyses allowed me to illuminate interactions between different mechanisms of sexual selection and to elucidate constraints on this sexually-selected trait. In contrast to central predictions of sexual selection theory, polygynous lemurs lack both sexual dimorphism in body size and male social dominance, but the degree of sexual dimorphism in the size of their canines is not known. A comparison of male and female canine size in 31 species of lemurs and lorises revealed significant male-biased canine dimorphism in only 6 of 13 polygynous lemur species. This result is in contrast to predictions of a hypothesis that would explain the lack of size dimorphism in lemurs as a result of high viability costs because canine teeth presumably have low maintenance costs and because they are used as weapons in male-male combat. Moreover, because females had significantly larger maxillary canines than males in only one lemur species, female dominance is not generally based on female physical superiority and selective forces favoring female dominance do not constrain sexual canine dimorphism in the sense of a pleiotropic effect. Contrary to predictions of sexual selection theory, species differences in canine dimorphism across strepsirhines were neither associated with differences in mating system, nor with the potential frequency of aggression. Variation in canine dimorphism was also unrelated to differences in body size, but there were significant differences among families, pointing to strong phylogenetic constraints. This study demonstrated that polygynous lemurs are at most subject to weak intrasexual selection on dental traits used in male combat and that traits thought to be under intense sexual selection are strongly influenced by phylogenetic factors.     

Morphological variability and developmental instability in subpopulations of the Eurasian badger (Meles meles) in Denmark

Aim Local populations from different geographical regions may differ in the selection regimes to which they are exposed. Differences in environmental factors and population density may affect the relative importance of different selective forces (e.g. natural vs. sexual selection). We suggest a direction of investigation concerned with the developmental instability of morphological traits. The goal is to disclose putative small‐scale geographical differences in the evolutionary forces, which may be hard to detect. Location Craniometrical investigations were carried out on ninety‐eight skulls and teeth of the Eurasian badger (Meles meles) collected during the period 1995–97 from three different populations in Denmark. One of these thrives at low population density, whereas the two others are characterized by high local density. Methods The skulls were investigated for developmental instability (DI) using fluctuating asymmetry (FA) as its estimator. FA was measured on canines, molars, premolar teeth and other skull and mandible traits. For the statistical analyses, we applied nonparametric permutation tests. Results Evidence was found suggesting differentiation among populations in mean degree of FA, and the FA values measured on canines were higher in the high‐density populations. FA of the canines was significantly higher in males than females, in contrast to FA of the other traits. Evidence of a negative relationship between canine size and their FA was found, whereas no significant correlations were found between the molar and premolar teeth measures and their FA. Main conclusions Our results suggest that canines could be under directional selection stemming from intrasexual competition, which may be stronger in high‐density zones. The other teeth investigated seem to be under a stabilizing regime hence their FA is mainly affected by environmental stresses. The negative relationship between canine size and FA found in males suggests the capacity of badgers to respond in an evolutionary way to environmental changes, despite the low genetic variability previously found at the molecular level.     

Sex determination in Miocene catarrhine primates

Canines of fossil hominoids and primitive catarrhines from several early, middle, and late Miocene sites were analyzed according to the shape indices described in Kelley (1995) and compared to those of males and females of extant great apes. In bivariate plots of the fossil canines utilizing the indices, 90% of the upper canines and 85% of the lower canines fell within or just outside the exclusively male or exclusively female territories delimited by the extant great apes. The remainder fell in the male-female overlap zones. Sex assignments based on these distributions were nearly 100% concordant with classifications according to canine height, suggesting a high degree of accuracy. There were various taxon-specific shifts in bivariate space among fossil genera, reflecting subtle differences in canine shape between taxa within the overall pattern of similarity to extant great apes as a whole. In many cases these shifts are matched by particular extant-ape species and subspecies, while other fossil taxa have no exact analogue for canine shape among the extant great apes. However, the pattern of spatial segregation of canines identified as either male or female at each of the sites largely mirrors that of males and females within the extant-ape sample, indicating that Miocene catarrhines shared with extant great apes a common pattern of shape differences between male and female canines, regardless of taxonspecific morphologies. These observations demonstrate that the canines of fossil catarrhines can be sexed with a high degree of confidence based solely on intrinsic features of shape. This will permit more reliable characterizations of morphological sexual dimorphism among fossil species. It is also argued that canine shape is a more reliable indicator of sex in fossil taxa than are canine/molar size ratios. © 1995 Wiley-Liss, Inc.     

Canine tooth strength and killing behaviour in large carnivores

Bending strength of upper canine teeth is examined among living canids, felids, hyaenids and several extinct species including sabretooth cats, borophagine dogs and the dire wolf, Canis dirus. The tooth is modelled as a cantilever with an elliptical cross-section. Using beam theory, the bending strength of the upper canine is calculated given a constant force applied to the canine tip. Results indicate that felids and hyaenids have relatively stronger canines than canids, particularly in bending about the anteroposterior (AP) rather than the mediolateral axis. It is suggested that canine shape reflects the forces produced during killing and feeding. As shown by an analysis of jaw muscle moment arms, felids and hyaenids have relatively stronger bites than canids. Moreover, the canines of hyaenids and felids are perhaps more likely to contact bone during feeding and killing and consequently may be subjected to larger and more frequent bending moments about the AP axis. The canines of sabretooth cats are shown to be more similar in shape and strength characteristics to those of living canids than felids, whereas those of the borophagine dogs and the dire wolf are closer to modern hyaenas.     

Canine Length in Wild Male Baboons: Maturation,Aging and Social Dominance Rank

Canines represent an essential component of the dentition for any heterodont mammal. In primates, like many other mammals, canines are frequently used as weapons. Hence, tooth size and wear may have significant implications for fighting ability, and consequently for social dominance rank, reproductive success, and fitness. We evaluated sources of variance in canine growth and length in a well-studied wild primate population because of the potential importance of canines for male reproductive success in many primates. Specifically, we measured maxillary canine length in 80 wild male baboons (aged 5.04–20.45 years) from the Amboseli ecosystem in southern Kenya, and examined its relationship with maturation, age, and social dominance rank. In our analysis of maturation, we compared food-enhanced baboons (those that fed part time at a refuse pit associated with a tourist lodge) with wild-feeding males, and found that food-enhanced males achieved long canines earlier than wild-feeding males. Among adult males, canine length decreased with age because of tooth wear. We found some evidence that, after controlling for age, longer canines were associated with higher adult dominance rank (accounting for 9% of the variance in rank), but only among relatively high-ranking males. This result supports the idea that social rank, and thus reproductive success and fitness, may depend in part on fighting ability mediated by canine size.     

Canine tooth size variability in primates

I present an analysis of canine tooth size variability in male and female primates. The coefficient of variation (CV = SD X 100/mean) as an index of canine size variability proved to be dependent on mean canine size in males and, to a lower extent, in females. Therefore, variability tends to increase with increasing values of mean canine size. Using residuals from the regression of log SD on log mean canine size in male and female primates, I analysed the contribution of diet, habitat and mating system to canine size variability. Habitat and mating system are known to influence to a certain extent the degree of sexual dimorphism in canine size. Given the well-known relationship between sexual dimorphism and phenotypic variability, it was suggested that these factors might influence variability in canine size. Everything else being equal, males of polygynous species are characterized by more variable canine sizes than males of monogamous species. Habitat and diet did not contribute to the level of variability observed in either males or females. It is proposed that a high level of variability in canine size may be related to the likelihood that enlarged canines evolved as a result of male-male competition for mates in polygynous species.     

Functional links between canine height and jaw gape in catarrhines with special reference to early hominins

This study tests the hypothesis that decreased canine crown height in catarrhines is linked to (and arguably caused by) decreased jaw gape. Associations are characterized within and between variables such as upper and lower canine height beyond the occlusal plane (canine overlap), maximum jaw gape, and jaw length for 27 adult catarrhine species, including 539 living subjects and 316 museum specimens. The data demonstrate that most adult male catarrhines have relatively larger canine overlap dimensions and gapes than do conspecific females. For example, whereas male baboons open their jaws maximally more than 110% of jaw length, females open about 90%. Humans and hylobatids are the exceptions in that canine overlap is nearly the same in both the sexes and so is relative gape (ca. 65% for humans and 110% for hylobatids). A correlation analysis demonstrates that a large portion of relative gape (maximum gape/projected jaw length) is predicted by relative canine overlap (canine overlap/jaw length). Relative gape is mainly a function of jaw muscle position and/or jaw muscle‐fiber length. All things equal, more rostrally positioned jaw muscles and/or shorter muscle fibers decrease gape and increase bite force during the power stroke of mastication, and the net benefit is to increase the mechanical efficiency during chewing. Similarly, more caudally positioned muscles and/or longer muscle fibers increase the amount of gape and decrease bite force. Overall, the data support the hypothesis that canine reduction in early hominins is functionally linked to decreased gape and increased mechanical efficiency of the jaws. Am J Phys Anthropol, 2013. © 2012 Wiley Periodicals, Inc.     

Interspecific and intraspecific relationships between tooth size and jaw size in primates

The association between mandibular robusticity, postcanine megadontia, and canine reduction in hominins has led to speculation that large and robust jaws might be required to spatially accommodate large canine and molar teeth in hominins and other primates. If so, then variations in mandibular form that are generally regarded as biomechanical adaptations to masticatory demands might instead be incidental effects of functional requirements of tooth support. While the association between large teeth and deep, robust jaws in hominins is well known, the relationship between tooth size and jaw size has not been systematically evaluated in a comparative sample of primates. We evaluate the relationships between molar tooth size, canine tooth size, and mandibular corpus and symphyseal dimensions in a sample of adult anthropoids in interspecific (n=84 species) and intraspecific (n=36 species) contexts. For intraspecific comparisons, tooth size and jaw size are correlated, but for a majority of species this is a function of sexual size dimorphism. Interspecific comparisons lend little direct support to the hypothesis that jaw breadth directly covaries with molar tooth breadth, but they do support the hypothesis that mandibular depth is associated with canine tooth size in males. The latter observation suggests that if there is a causal association between canine size and mandibular depth, it is subject to a threshold effect. In contrast, neither corpus nor symphyseal robusticity, measured as a shape index of breadth/height, are correlated with tooth size. Our results suggest that further studies of the relationship between tooth size and corpus morphology should focus on tooth root size and corpus bony architecture, and that species-specific factors should have a strong impact on such relationships.     

Canine dimorphism

Canine dimorphism in many primates is exaggerated, with males possessing enormous, sharp canines that project far beyond the occlusal plane of the other teeth and females having smaller, less projecting canines. Ever since Darwin,¹ canine dimorphism generally has been attributed to sexual selection. However, recent analyses suggest that the evolution of canine dimorphism is complex and that the sexual selection hypothesis is only part of the story.     

Evolutionary dental changes.

In the evolution of primates there has been a tendency towards reduction in jaw length and prognathism, mandibular canine size and first molar cusp number, and third molar presence. These oral structures were contrasted, and compared with cranial size, body height and weight, and finger length in 118 males and 102 females of the Burlington Growth Centre. Body weight was significantly related to canine width and to jaw length and prognathism. These relationships were stronger in the males than in the females. The evolutionary reduction in these dental dimensions may result from an evolutionary reduction in genetically determined body size. In the males the number of molar cusps was related to finger length and cranial height. Agenesis of third molars was related to the length of the maxilla in both sexes. In the females, canine width was related to the number of cusps of the first molars, agenesis of third molars, and length of a finger. Simultaneous reductions in dental structures were more frequent in the females.     

Sexual dimorphism of root length on a Greek population sample

Sexual dimorphism in teeth has been an area of research for osteoarchaeologists and forensic anthropologists studying human skeletal remains. As most studies have been based on the mesiodistal and buccolingual crown measurements, sexual dimorphism from root length dimensions remains “neglected” by comparison to crown dimensions. The aim of the present study was to test the existence of sexual dimorphism in the root length of single-rooted teeth with the purpose of investigating whether maximum root length can be reliably used to determine sex. A total of 774 permanent teeth in 102 individuals (58 males and 44 females) from the Athens Collection were examined. The maximum root length of each tooth was measured on the mesial, distal, buccal, and lingual side. Almost all teeth presented a high degree of sexual dimorphism with males showing numerically higher values in root length than females. The most dimorphic teeth were the maxillary second incisors followed by maxillary canines. The percentage of sexual dimorphism reached 16.56%, with maxillary teeth showing the highest degree of dimorphism. The classification results show that the overall correctly specified group percentage ranged from 58.6% to 90.0%. The data generated from this study suggest that root length measurements offer a reliable method for determining sex and are therefore useful in osteoarchaeological studies, particularly in cases of fragmented or cremated material, but also in forensic contexts. Moreover, root length can be used to separate the remains of female and male subadult individuals with a high level of accuracy thus addressing one of the most problematic issues in human osteoarchaeology and anthropology as immature skeletons are the most difficult to sex.     

Redescription of a poorly known acropomatid, <Emphasis Type="Italic">Verilus sordidus</Emphasis> Poey 1860, and comparison with <Emphasis Type="Italic">Neoscombrops atlanticus</Emphasis> Mochizuki and Sano 1984 (Teleostei: Perciformes)

A poorly known acropomatid, Verilus sordidus Poey 1860, is redescribed based on six specimens from the western central Atlantic. We present diagnostic characters to differentiate this species from Neoscombrops atlanticus Mochizuki and Sano 1984, which has been confused with this species, and designate a neotype of V. sordidus. This species is distinguishable from N. atlanticus by the proximal-middle radial of the first anal-fin pterygiophore being slender with no trough or hollow on the anterodorsal portion (vs. hollow in N. atlanticus), several canine teeth posterior to the large canine teeth on either side of the symphysis of the lower jaw (vs. villiform teeth posterior to enlarged canines), and by the modal numbers of pectoral-fin rays, lateral-line scales, and gill rakers on the lower limb of the first arch.