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Body size is a key determinant of male fighting ability and reproductive success in many animal species, but relationships between these variables have only rarely been examined in group-living animals in which body size often correlates with dominance rank. We examined the relationships between body size (crest height, back breadth and body length), dominance rank, alpha male tenure length, number of adult females and patterns of aggression in 26 wild adult male mountain gorillas, Gorilla beringei beringei, living in multimale groups. A composite measure combining crest height and back breadth (variables were highly correlated and combined into a crest–back score), but not body length, significantly correlated with dominance rank, alpha male tenure length and number of adult females per group. The alpha male had the largest crest–back score in six of the seven groups, and in the majority of dyads the male with the higher crest–back score was higher ranking. The frequency (and intensity on mating days) of aggressive contests was higher between males close in rank. Additionally, aggression occurred more frequently when the initiator was larger than the recipient. Our results suggest that factors other than body size are likely to influence dominance rank, but large size helps males attain and retain high dominance rank, probably leading to greater reproductive success. Further studies on how the timing and intensity of male–male competition influences life history trade-offs between investment in secondary sexual characteristics, body condition and survival may explain variance in lifetime reproductive success within and between species.

The ability to accurately measure morphological characteristics of wild primates in the field is challenging, yet critical for understanding fundamental aspects of their biology and behavior. Recent studies have shown that digital photogrammetry can be used to non-invasively measure morphological traits of wild primates, as it allows for the determination of geometric properties of objects remotely from photographic images. We report here on a rare opportunity to test this methodology by comparing measurements obtained directly from living great apes to those obtained from photographs. We test the accuracy and precision of two independent photogrammetric techniques, employing the use of parallel lasers and a distance meter, respectively, for obtaining measurements of static objects and captive western lowland gorillas (Gorilla gorilla gorilla) (n = 4) at Zoo Atlanta. For static objects, the mean percent error between corresponding measurements collected by the same observer directly versus using photogrammetry was 0.49-0.74% for the parallel laser method and 0.62-0.76% for the distance meter method. For gorillas, mean percent error between corresponding direct and remote measurements was 2.72-5.20% for the parallel laser method and 2.20-7.51% for the distance meter method. Correlations between direct measurements and corresponding parallel laser and distance meter measurements of gorillas were highly significant with R2 values and slopes approaching 1.0 (parallel lasers: R2 = 0.9989, P

Molars are highly integrated biological structures that have been used for inferring evolutionary relationships among taxa. However, parallel and convergent morphological traits can be affected by developmental and functional constraints. Here, we analyze molar shapes of platyrrhines in order to explore if platyrrhine molar diversity reflects homogeneous patterns of molar variation and covariation. We digitized 30 landmarks on mandibular first and second molars of 418 extant and 11 fossil platyrrhine specimens to determine the degree of integration of both molars when treated as a single module. We combined morphological and phylogenetic data to investigate the phylogenetic signal and to visualize the history of molar shape changes. All platyrrhine taxa show a common shape pattern suggesting that a relatively low degree of phenotypic variation is caused by convergent evolution, although molar shape carries significant phylogenetic signal. Atelidae and Pitheciidae show high levels of integration with low variation between the two molars, whereas the Cebinae/Saimiriinae, and especially Callitrichinae, show greater variation between molars and trend toward a modular organization. We hypothesize that biomechanical constraints of the masticatory apparatus, and the dietary profile of each taxon are the main factors that determine high covariation in molars. In contrast, low molar shape covariation may result from the fact that each molar exhibits a distinct ecological signal, as molars can be exposed to distinct occlusal loadings during food processing, suggesting that different selective pressures on molars can reduce overall molar integration.

Tooth morphology has been widely used to infer taxonomic affinities. Both morphological and genetic analyses have revealed significant differences among capuchins, suggesting that two distinct monophyletic groups exist: the gracile capuchins (Cebus) and the robust capuchins (Sapajus). We developed a geometric morphometrics (GM) model to determine if the two groups also show distinct molar shapes and to explore the influence of size, phylogeny, and biogeography in shaping molar morphology. We characterized first and second molar crown shape variability in seven species representative of the two genera (Cebus albifrons, C. olivaceus, Sapajus apella, S. robustus, S. libidinosus, S. nigritus, and S. xanthosternos), using two-dimensional (2D) and three-dimensional (3D) GM. The results showed that 2D GM discriminated the two groups better than 3D GM, possibly because it accounted for cusp position and crown contour, but not cusp height, which may be a useful trait for inferring adaptive foraging ecology but presents a risk of homoplasy. In addition, the presence of a phylogenetic signal in the first molar shape (2D) is likely to reflect similarity to the ancestral condition and provides evidence of gradual evolution of molar robustness in the robust clade. We suggest that the shape of the first molar is informative about phylogenetic affinities, whereas the shape of the second molar is more informative about biogeographic variability. However, molar shape similarities may be affected by convergent evolution, as environmental factors in different biogeographical regions may have a significant effect on molar morphology, as seen in the closely related capuchins.

Morphometric variation of biological structures has been widely used to determine taxonomic affinities among taxa, and teeth are especially informative for both deep phylogenetic relationships and specific ecological signals. We report 2-dimensional geometric morphometrics (GM) analyses of occlusal crown surfaces of lower molars (M1, n = 141; M2, n = 158) of cercopithecoid primate species. A 12-landmark configuration, including cusp tips and 8 points of the molar crown contour, were used to evaluate patterns of variation in lower molar shape among cercopithecoid primates and to predict the taxonomic attribution of 2 archaeological macaques from Roman time periods. The results showed that the lower molar shape of cercopithecoid primates reflects taxonomic affinities, mostly at a subfamily level and close to a tribe level. Thus, the cusp positions and crown contour were important elements of the pattern related to interspecific variation. Additionally, the archaeological specimens, attributed to Macaca sylvanus based on osteological information, were classified using the GM molar shape variability of the cercopithecoid primates studied. The results suggest that their molar shape resembled both M. sylvanus and M. nemestrina, and species attribution varied depending on the comparative sample used.

We measured the molar size from a single population of wild baboons from Amboseli (Kenya), both females (n = 57) and males (n = 50). All the females were of known age; the males represented a mix of known-age individuals (n = 31) and individuals with ages estimated to within 2 years (n = 19). The results showed a significant reduction in the mesiodistal length of teeth in both sexes as a function of age. Overall patterns of age-related change in tooth size did not change whether we included or excluded the individuals of estimated age, but patterns of statistical significance changed as a result of changed sample sizes. Our results demonstrate that tooth length is directly related to age due to interproximal wearing caused by M2 and M3 compression loads. Dental studies in primates, including both fossil and extant species, are mostly based on specimens obtained from osteological collections of varying origins, for which the age at death of each individual in the sample is not known. Researchers should take into account the phenomenon of interproximal attrition leading to reduced tooth size when measuring tooth length for ondontometric purposes.

Analyses of buccal tooth microwear have been used to trace dietary habits of modern hunter-gatherer populations. In these populations, the average den-sity and length of striations on the buccal surfaces of teeth are significantly cor-related with the abrasive potential of food items consumed. In non-human pri-mates, tooth microwear patterns on both occlusal and buccal wear facets have been thoroughly studied and the results applied to the characterization of dietary habits of fossil species. In this paper, we present inter- and intra-specific buccal microwear variability analyses in extant Cercopithecoidea (Cercopithecus mitis, C. neglectus, Chlorocebus aethiops, Colobus spp., Papio anubis) and Hominoidea (Gorilla gorilla, Pan troglodytes, Pongo pygmaeus). The results are tentatively compared to buccal microwear patterns of the Miocene fossils Dryopithecus and Oreopithecus. Significant differences in striation density and length are found among the fossil taxa studied and the extant primates, sug-gesting that buccal microwear can be used to identify dietary differences among taxa. The Dryopithecus buccal microwear pattern most closely resembles that of abrasive, tough plant foods consumers, such as the gorilla, in contrast to stud-ies of dental morphology that suggest a softer, frugivorous diet. Results for Ore-opithecus were equivocal, but suggest a more abrasive diet than that previously thought.