Patterns of sexual dimorphism and of variability in the dentition ofOtolemur crassicaudatus

Normative odontometric data are presented on a sample of 66 adult thick-tailed bushbabies Otolemur crassicaudatus(34 male, 32 female). This species is characterized by low levels of sexual dimorphism, with univariate differences centered on the canines and the maxillary third molar. Multivariate canonical analysis isolates a third discriminator, the maxillary second molar. Stepwise discriminant analyses, performed after jackknifing, indicate high percentages of correct classification (males, 79.8–81.8%;females, 81–85.2%). When variability profiles consisting of arrays of CVs are compared, males and females are found to share similar patterns. Data for maxillary teeth offer support for Gingerich’s occlusal complexity model, while morphogenetic clusterings within regressions of variability on tooth size conform to those previously reported in other species. These relationships are lost in the mandibular dentition, suggesting an independence of upper from lower toothsize determination.     

Odontometric differences betweenCercopithecus aethiops populations: A simulation approach to estimating confidence limits for Penrose’s shape coefficient

A modified bootstrapping procedure is described by means of which standard errors and confidence limits may be determined for the Penrose shape coefficient. This method is then applied to odontometric data derived from four closely related groups of primates: Cercopithecus aethiops pygerythrus, C. a. sabaeus,St. Kitt’s green monkey (derived from C. a. sabaeus),and C. a. centralis.Although statistically significant distances were found to exist between these groups, one shape coefficient was significantly greater than the others: that between C. a. pygerythrusand C. a. centralis.Low levels of sexual dimorphism characterized the shape coefficients, with distances based on mandibular teeth being greater than those derived from maxillary teeth.     

The dentition of the Indian Knoll skeletal population: odontometrics and cusp number.

Data on the permanent dentition of 153 individuals from the well known Indian Knoll skeletal population are presented. Mesiodistal and buccolingual measurements were taken with a Helios dial caliper. Cusp number of maxillary and mandibular molars are recorded. The Indian Knoll dentition is larger than many modern groups but smaller than Australoid or Mesolithic groups. With the exception of maxillary 12, males have larger teeth than females in both dimensions. The lower canine is the most dimorphic tooth. Through rank order correlation, an association was shown between the sexual dimorphism of the mesiodistal and buccolingual dimensions. Compared to modern groups, the Indian Knoll population displays a moderate degree of sexual dimorphism in tooth size. In general, the coefficients of variation were greater for the more distal teeth within morphological classes. Amounts of size variability did not differ significantly between the sexes; moreover, rank order correlations indicated that patterns of variability in both dimensions were similar for males and females. The predominant cusp number pattern for upper molars is 4-3-3 and for lowers 5-5(4)-5. No sex differences were shown for cusp occurrence or bilateral asymmetry in cusp number.     

Cranial variability in East African ‘Robust’ hominis

Among Plio-Pleistocene hominins the East African ‘robust’ group [Australopithecus (Paranthropus) boisei sensu lato] has the largest sample. This makes it an important test case for examining within-group variability and its implications for early hominin systematics. When using the CV to test for mixed-species samples, sexual dimorphism and diachronic variation are important additional (confounding) sources of variability. After examining nineteen variables, five craniometric variables in the East African ‘robust’ group are identified that have low sexual dimorphism. All are characterised by CVs from a combined KNM-WT 17000 andA. (P.) boisei sample less than the CV of the bonobo. Diachronic variation is found to be an important source of variability for cranial capacity. This form of variation cannot be detected in other variables studied here, but its possible presence cannot be ignored (owing mostly to small sample sizes). It is concluded that there is insufficient evidence to refute the hypothesis that all East African ‘robust’ fossils belong toA. (P.) boisei (Walker and Leakey, 1988).     

Tooth size and arcadal length correlates in man

Intra-arcadal mesiodistal and buccolingual tooth size correlations were evaluated in a sample of 125 caucasoids with ideal occlusion. Dental dimensions were corrected for arcade mength (as a measure of jaw size) by a series of regression analyses of each mesiodistal dimension on the sum of the mesiodistal dimensions within each arcade. Regression coefficients of tooth dimension on arcade length were calculated to gain an insight into the dimensional sensitivity of individual teeth to arcade length variation. The data presented here suggest a strong association between arcadal length (jaw size) dependence, and the dimensional stability of individual teeth. When corrected for arcade length, a definite pattern of tooth size correlation emerges: postcanine maxillary and mandibular teeth are negatively correlated to the anterior teeth and are positively correlated to one another. The hypothesis is developed that anterior and postcanine teeth should be viewed as two separate and negatively size-correlated units, beyond the boundaries of the four morphological tooth classes. Recognition of this basic dichotomous size arrangement within each jaw allows for a reassessment of some of the problems associated with hominid dental evolution.     

Differences in Tooth Microwear of Populations of Caribou (<Emphasis Type="Italic">Rangifer tarandus</Emphasis>, Ruminantia,Mammalia) and Implications to Ecology,Migration, Glaciations and Dental Evolution

Tooth microwear was analyzed for a large sample of wild-shot barren-ground caribou (Rangifer tarandus groenlandicus) from the Kaminuriak population of eastern Canada. This sample was compared to the microwear of specimens from three Pleistocene localities in North America (Alaska) and western Europe (Caune de l’Arago in France and Salzgitter in Germany). The results show that the extant samples from eastern Canada have seasonal variation in microwear and presumably in diet. The differences in microwear between the various seasons may reflect a cyclic migration of the population within a year. The extinct population from Alaska has extremely blunt teeth (mesowear), as blunt as those of modern zebras and bison. This observation is corroborated by the lowest number of microwear pits. The findings are untypical, as most typical caribou teeth have sharper apices, and we interpret this as an indication of a local habitat that was different with animals feeding on non-typical vegetation. The combination of Rangifer from Caune de l’Arago and Salzgitter reveals a pattern in microwear variability. The Salzgitter is interglacial and shows a greater diversity of browsing (broad spectrum on average number of pits) than the glacial Caune de l’Arago. The interglacial population from Salzgitter is interesting because it shows several different types of browsing. Collectively all the Rangifer teeth show that diet of a brachydont taxon can vary across most of the dietary morphospace of ungulates as represented by tooth microwear. The three Pleistocene samples exhibit microwear that is different from the extant population in question. This observation implies that the recent diet of Rangifer has changed from the typical caribou diet in the past. This indicates dietary change within a species. This is important because it represents dietary evolution without changes in tooth morphology.     

Sexual dimorphism in modern human permanent teeth

On average, males possess larger tooth crowns than females in contemporary human populations, although the degree of dimorphism varies within different populations. In previous studies, different amounts of either enamel or dentine were implicated as the cause of this dimorphism. In this study, we attempt to determine the nature of sexual dimorphism in the crowns of permanent modern human teeth and to determine if two contrasting tooth types (permanent third molars and canines) show identical patterns of dimorphism in enamel and dentine distribution. We estimated the relative contributions of both enamel and dentine to total crown size, from buccolingual sections of teeth. Our sample consisted of a total of 144 mandibular permanent third molars and 25 permanent mandibular canines of known sex. We show that sexual dimorphism is likely due, in part, to the presence of relatively more dentine in the crowns of male teeth. However, whatever the underlying cause, dimorphism in both tooth root and tooth crown size should produce measurable dimorphism in tooth weight, though this has not been previously explored. Therefore, we provide some preliminary data that indicate the usefulness of wet tooth weight as a measure of sexual dimorphism. Both male permanent third molars and canines are significantly heavier than those of females. The weight dimorphism reported here for both classes of teeth may prove a useful finding for future forensic studies. In particular, weights of canines may be more useful as a means of sexing modern human skeletal material than linear or area measurements of teeth.     

Numerical analysis of sexual dimorphism inSaguinus dentition

Among New World monkeys, more or less sexual dimorphism exists in the dentition, especially in the Cebidae. On the other hand, the Callitrichidae includingSaguinus are said to be characterized by a broad lack of sexual dimorphism with the exception of the reproductive organs. In the present article, sexual dimorphism in the dentition of someSaguinus species was reconfirmed using univariate and multivariate analytical methods. The results of the analysis were as follows: (1) there is no sexual dimorphism in the canine tooth size, except for the upper canine ofS. geoffroyi and lower canine ofS. mystax; (2) the overall tooth size difference between males and females is slight or none inS. geoffroyi, S. leucopus, andS. fuscicollis, relatively small inS. oedipus andS. mystax, and rather larger inS. midas; (3) an overall difference in shape factor between both sexes exists in all species ofSaguinus to a greater or lesser extent; (4) although only slight sexual dimorphism is recognized in the canine tooth itself, sexual dimorphism does exist in some adjacent teeth of the canine in a few species; and (5) there are some interspecific differences in the magnitude of the sexual dimorphism of theSaguinus dentition and these differences are more evident in species inhabiting the peripheral regions of the distribution areas of this genus. Taking all the evidence obtained into account, the sexual dimorphism in theSaguinus dentition must be re-investigated in comparison with other genera of the Callitrichidae.     

Evolutionary and climatic factors affecting tooth size in the red foxVulpes vulpes in the Holarctic

Research into the geographical pattern of tooth size in the red fox,Vulpes vulpes (Linnaeus, 1758) in the Holarctic was conducted on a sample of 3806 skulls belonging to 41 fox populations. The Nearctic was represented by 948 specimens (249 females, 359 males, 340 specimens of unknown sex) belonging to 13 populations, whereas the Palearctic was represented by 2858 red foxes (1034 females, 1256 males, 568 specimens of unknown sex) from 32 populations. In the Nearctic, the largest foxes live on Kodiak Island (V. v. harrimani) and the Kenai Peninsula (V. v. kenaiensis), while the smallest ones live in California (V. v. necator) and Georgia (V. v. fulvus). In the Palearctic, the largest foxes come from the Far East (V. v. jakutensis, V. v. beringiana, V. v. tobolica), while the smallest are from the southern borders of the Eurasian range (V. v. pusilla, V. v. barbara, V. v. arabica). In both the Palearctic and Nearctic, tooth size in the fox varies depending on the geo-climatic factors. The fox’s tooth size confirms the general basis of Bergmann’s rule. In the Palearctic, specimens with larger teeth occur in cooler habitats with greater seasonality. These are first and foremost Northern and Far Eastern populations. In the Nearctic, tooth size in red foxes depends on the temperature and humidity of their habitat. Competition within the species and between species has important impact on the variation and dimorphism of tooth size in the red fox. Both in the Nearctic and Palearctic, red foxes from regions of sympatric co-occurrence with other closely relatedVulpes species, are more sexually dimorphic in terms of tooth size than red foxes from allopatric regions. Analysis of morphological distance on the basis of the size of dental characteristics shows, that in the Palearctic, the foxes from India (V. v. pusilla), while in the Nearctic, the population from Kodiak Island (V. v. harrimani) are most distant from the remaining populations. Geographic barriers such as the Bering Strait, Parry Channel, Mackenzie River, Kolyma and Omolon River systems have had a critical impact on red fox evolution. The most likely place for the evolution and diversification of the phyletic lineVulpes vulpes seems to be the Middle East region.     

The size and morphology of the Nasioi dentition

Dental impressions were obtained on 240 Nasioi, a Melanesian population living on the island of Bougainville. Odontometric data are presented for both the permanent and deciduous teeth, and the former teeth are also examined morphologically. The results show that the Nasioi have large permanent teeth like other Australoid populations whereas the deciduous teeth are only of moderate size. The coefficients of variation are large in the permanent teeth compared to other populations but the sexual dimorphism in tooth size and variability is not remarkable. Morphologically, the permanent teeth of the Nasioi are characterized by a cusp number pattern, a high frequency of the Dryopithecus + pattern on the first mandibular molar, few individuals with a Cusp of Carabelli, and a moderate expression of shovelled-shaped anterior teeth.     

Critique of ‘Australopithecus afarensis’ as a single species based on dental metrics and morphology

Leonard andHegmon (1987) compare a series of dental metrics of ‘Australopithecus afarensis Johanson, White, andCoppens, 1978’ with criteria for modern apes, to test the hypothesis that ‘A. afarensis’ represents a single species. They also compare the morphology of the lower third premolar. The dental breadth of ‘A. afarensis’ shows a wide range of variation, particularly in the lower third premolar morphology which displays greater variation than in modern apes—yet the study concludes that the single species hypothesis cannot be rejected. The study is flawed by applying criteria for pongids inappropriate for a hominid. When ‘A. afarensis’ is compared with criteria for hominids, the range of variation in dental size, breadth, and third premolar morphology is greater than that in any hominid species. The single species hypothesis is, therefore, once again rejected. Moreover, the name ‘A. afarensis’ is preoccupied byPraeanthropus africanus (Weinert) and must be dropped.     

Patterns of metric variability in the dentition of Papio ursinus

The present investigation assesses a number of explanations for the patterns of variability in dental dimensions. Coefficients of variation were calculated for mesiodistal and buccolingual diameters in a sample of 105 Papio ursinus crania (52 male, 53 female). Variability profiles consisting of arrays of values of coefficients of variation were evaluated by means of Friedman's two-way analysis of variance and Kendall's coefficient of concordance. Although molar teeth were found to be the most dimensionally stable, our results failed to support either the morphogenetic field theory or the occlusal complexity hypothesis. The data presented here are generally supportive of Pengilly's phenotypic complexity theory. However, speciesspecific clustering patterns found in our regressions of dimensional variability on mean tooth size suggest that differences in variability levels might be related to differences in selective pressures.     

An odontometric analysis of the early Griqua dentition

The teeth of 28 Griqua skeletons were subjected to odontometric analysis. Significant sexual dimorphism in tooth size was demonstrated in canines and molars. Coefficients of variation were generally greater in the more distal tooth within morphological classes. Rank order correlations suggest similar patterns of variability in males and females. Comparisons of the Griqua dentition with similar populations were made.     

Metric variation and sexual dimorphism in the dentition of Ouranopithecus macedoniensis

The fossil sample attributed to the late Miocene hominoid taxon Ouranopithecus macedoniensis is characterized by a high degree of dental metric variation. As a result, some researchers support a multiple-species taxonomy for this sample. Other researchers do not think that the sample variation is too great to be accommodated within one species. This study examines variation and sexual dimorphism in mandibular canine and postcanine dental metrics of an Ouranopithecus sample. Bootstrapping (resampling with replacement) of extant hominoid dental metric data is performed to test the hypothesis that the coefficients of variation (CV) and the indices of sexual dimorphism (ISD) of the fossil sample are not significantly different from those of modern great apes. Variation and sexual dimorphism in Ouranopithecus M(1) dimensions were statistically different from those of all extant ape samples; however, most of the dental metrics of Ouranopithecus were neither more variable nor more sexually dimorphic than those of Gorilla and Pongo. Similarly high levels of mandibular molar variation are known to characterize other fossil hominoid species. The Ouranopithecus specimens are morphologically homogeneous and it is probable that all but one specimen included in this study are from a single population. It is unlikely that the sample includes specimens of two sympatric large-bodied hominoid species. For these reasons, a single-species hypothesis is not rejected for the Ouranopithecus macedoniensis material. Correlations between mandibular first molar tooth size dimorphism and body size dimorphism indicate that O. macedoniensis and other extinct hominoids were more sexually size dimorphic than any living great apes, which suggests that social behaviors and life history profiles of these species may have been different from those of living species.     

Male or female soldiers? An evaluation of several factors which may influence soldier sex ratio in lower termites

In termites, the soldiers’ sex ratio is often biased toward one sex. Unlike in the Hymenoptera, this bias cannot easily be explained by relatedness asymmetries because termites are diploid. Matsuura proposed that when large body size is adaptive for colony defence (e.g. in case of phragmotic defence) then the larger sex (given sexual size dimorphism exists) should be more likely to reach a threshold size and develop into soldiers. This would explain biased sex ratios. Matsuura validated his hypothesis for four Reticulitermes species. Here, we tested his hypothesis for two species of Cryptotermes with phragmotic defence. These drywood termites have a life type that is thought to be ancestral in termite’s evolution, thus giving us potential insights into the evolution of the soldier caste. In one of these species, the sex ratio of soldiers was highly female biased, but we could not support Matsuura’s hypothesis. Both species lacked sexual size dimorphism in all castes. Additionally, in both species, the sex ratio of helpers and sexuals did not deviate from a 1:1 ratio, and hence can also not account for the bias observed in soldiers. However, this study showed that there were behavioural differences between the sexes in both species, which could shed some light on biased sex ratio in soldiers. Our findings also indicate that the developmental pathway taken by individuals reflects a ‘decision’ at the colony level. The discovery of behavioural differences between sexes in termites should open the way to similar studies in other taxa with helpers/ workers of both sexes, as it might reveal more task partitioning in colonies than previously thought and it raises questions concerning the selective pressures that acted on caste evolution in termites. Received 30 October 2007; revised 17 January and 27 February; accepted 4 March 2008.     

Postcanine tooth size in female primates

The results of many allometric studies of postcanine tooth size in mammals have not corresponded to expectations of tooth size based on energy requirements and dental function. The purpose of this study is to investigate the relationship between postcanine occlusal surface area, body size, and the metabolic demands of pregnancy and lactation in female primates. Tooth and body sizes from 38 primate species were taken from the literature to test two hypotheses: 1) females should have relatively larger teeth than males in order to masticate additional food for the energetic costs of reproduction; 2) taxa with the largest neonatal size (a measure of average metabolic costs of pregnancy and lactation) should have females with a greater degree of relative dental enlargement. The results show that relatively large female teeth are not found consistently in primate species. Females have less occlusal surface area than expected on the basis of the male tooth and body size regression in 21% of the species, and there is no correlation between relative female tooth size and relative newborn size across higher primate taxa. The degree of female dental enlargement is most closely related to degree of sexual dimorphism in body weight. The correlation between degree of body weight dimorphism and relatively larger postcanine teeth in females than in males is 0.87 in the 38 species. Species that are monomorphic in weight tend to be monomorphic in tooth size even though females apparently require more food than males.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ontogenetic bases of canine dimorphism in anthropoid primates

This study tests hypotheses regarding the ontogeny of canine tooth size dimorphism in five anthropoid primate species (Saguinus fuscicollis, Macaca mulatta, Cercocebus atys, Papio hamadryas, and Mandrillus sphinx). Canine measurements and chronological age data are analyzed to determine if bimaturism, a sex difference in the age at which eruption ceases, accounts for canine tooth sexual dimorphism. Canine height measurements are evaluated through a variety of regression techniques. Results show a lack of sexual dimorphism in Saguinus. While size dimorphism is absent in the deciduous teeth of all species analyzed, the adult teeth in cercopithecines become increasingly dimorphic through ontogeny. Female adult tooth eruption regularly precedes male tooth eruption, and regression-based eruption trajectories for both sexes intersect at about the age at which the female tooth reaches adult size. Males erupt the tooth later and more rapidly than females. Males also reach a larger adult size than females by erupting the tooth for much longer periods of time. Bimaturism is primary in the production of dimorphism, but rates of eruption show modest variation. These results point to the scheduling of sexual selection through intermale competition as a primary factor determining male eruption timing, rates of eruption, and adult size. Life history factors may play a role in determining the relations between the scheduling of intrasexual competition and canine eruption. Female contributions to sexual dimorphism are apparent in these species, suggesting that similar levels of dimorphism can be attained through diverse ontogenetic pathways.     

Tooth Size Variation in Assemblages of Tremacyllus (Hegetotheriidae,Notoungulata): Insights into Geographical Gradients,Systematics, and Sexual Dimorphism

Tooth size variation within fossil assemblages can be associated with intra- or interspecific variation, functional, developmental, and geographical factors, and/or sexual dimorphism. Understanding these sources of variation is necessary to develop diagnoses for fossil mammals, where teeth are usually the most frequent remains. Tremacyllus (Ameghino, 1891) (Hegetotheriidae, Notoungulata) is a genus of small-sized herbivorous mammals abundant in late Miocene to Pliocene outcrops of southern South America. Its simplified, euhypsodont dentition and size variability have hampered systematics studies and led, for instance, to an overestimation of the number of species. I analyzed tooth size variations within assemblages of Tremacyllus in a quantitative framework to test three hypotheses: (1) magnitudes of size variation are different among tooth loci and assemblages; (2) tooth size follows a geographical pattern within the analyzed sample (Bergmann’s rule), but is also associated with taxonomy; and (3) there is a correlation between size variation and sexual dimorphism reflected in distinguishable subgroups. Results indicate that patterns of variation might be associated with eruption time and/or functional position. Northwestern forms are larger than southwestern-Pampean ones, not conforming to Bergmann’s rule but revealing a strong influence of latitude. Size differences between assemblages agree with dental features that distinguish T. incipiens and T. impressus, allowing expanded species diagnoses. Two size subgroups might reflect sexual dimorphism in the absence of biostratigraphic or morphological differences between them. This interpretation indicates that northwestern specimens referred to T. diminutus should be referred to T. incipiens.

     

Environmental influences on the sexual dimorphism in body size of western bobcats

Sexual size dimorphism might be influenced by environmental constraints on sexual selection or by intraspecific competition between males and females. We studied bobcats (Lynx rufus) in collections of museum specimens from western North America to examine these hypotheses. Structural body size was estimated from several measurements of the skull, ln-transformed and indexed through principal components analysis. Sexual dimorphism in body size was estimated from the difference in size index of males and females, and compared to geographic and climatic variables associated with biotic provinces (ecoregions). Of several climatic variables that were associated with bobcat body size, only seasonality of climate was associated with sexual dimorphism. Sexual size dimorphism, longitude, elevation, and seasonality were intercorrelated. As longitude decreased (moving inland from west-coastal ecoregions), sexual dimorphism decreased with the increased elevation and seasonality of continental climates of the Rocky Mountains. We suggest that increased seasonality and the need for fasting endurance by females may place constraints on the degree of sexual dimorphism in bobcats. Sexual dimorphism of body size and sexual size dimorphism of trophic structures (teeth) exhibited a strong positive association over geography, thus indirectly supporting the hypothesis that intrasexual competition for prey could account for the geographic variation in sexual size dimorphism. Thus, both environmental constraints on sexual selection of body size and intersexual competition were supported as possible explanations of the degree of sexual size dimorphism that occurs in populations of bobcats.