Sexual dimorphisms in dental dimensions of higher primates

Dental dimensions and distributions of dental dimensions of males and females were compared for great apes (Pan, Gorilla, and Pongo, and humans (Homo). The results were examined and discussed with reference to fossil primates Sivapithecus and Ramapithecus. The analyses focused on patterns of sexual dimorphism, both with regard to mean dimensions and the distribution of those dimensions. Sex differences in mean canine dimensions were large and significant for Gorilla and Pongo, significant but smaller for Pan, and small but occasionally significant for Homo. The dispersions of measures were greater for males than for females in Gorilla and Pan but did not differ significantly for Pongo or Homo. Examination of the noncanine teeth revealed complex sex differences. In the anterior teeth, sex differences in mean dimensions were generally apparent for Gorilla and Pongo, less so for Pan, and least of all in Homo. The patterns of dispersion of measures of anterior teeth differed markedly from those of the canines. Pan exhibited the same pattern for anterior and canine teeth. Gorilla showed the opposite pattern. Pongo and Homo showed similar dispersions for males and females in many cases. Sex differences in posterior teeth followed the pattern of the canines for Gorilla and were absent for Pan. Pongo exhibited mean differences in dimensions across sex, but dispersions were similar. The pattern for Homo was most like that of Pongo, but with fewer significant differences. The genera differed with regard to the number of significant differences in means or dispersions along the tooth row. It is clear that the patterns of dimorphism differ qualitatively across all extant genera of great apes and humans. It appears that the pattern for Homo most closely resembles that of Ramapithecus, whereas Pongo most closely resembles Sivapithecus. The patterns for Gorilla and Pan appear to be unlike either of the fossil forms. It is suggested that the qualitatively distinct patterns of dental sexual dimorphism indicate substantial flexibility during recent primate evolution and that the degree of structural flexibility demonstrated provides a basis for appreciating potential for plasticity of gender differences in behavioral, social, and cultural systems.     

Body size and its consequences: Allometry and the lower limb length of Liang Bua 1 (Homo floresiensis)

Bivariate femoral length allometry in recent humans, Pan, and Gorilla is investigated with special reference to the diminutive Liang Bua (LB) 1 specimen (the holotype of Homo floresiensis) and six early Pleistocene femora referred to the genus Homo. Relative to predicted body mass, Pan and Gorilla femora show strong negative length allometry while recent human femora evince isometry to positive allometry, depending on sample composition and line-fitting technique employed. The allometric trajectories of Pan and Homo show convergence near the small body size range of LB 1, such that LB 1 manifests a low percentage deviation (d_yx of Smith [1980]) from the Pan allometric trajectory and falls well within the 95% confidence limits around the Pan individuals (but also outside the 95% confidence limits for recent Homo). In contrast, the six early Pleistocene Homo femora, belonging to larger individuals, show much greater d_yx values from both Pan and Gorilla and fall well above the 95% confidence limits for these taxa. All but one of these Pleistocene Homo specimens falls within the 95% confidence limits of the recent human sample. Similar results are obtained when femoral length is regressed on femoral head diameter in unlogged bivariate space. Regardless of the ultimate taxonomic status of LB 1, these findings are consistent with a prediction made by us (Franciscus and Holliday, 1992) that hominins in the small body size range of A.L. 288-1 (“Lucy”), including members of the genus Homo, will tend to possess short, ape-like lower limbs as a function of body size scaling.     

Australopithecines: Ancestors of the African Apes?

Since australopithecines display humanlike traits such as short ilia, relatively small front teeth and thick molar enamel, they are usually assumed to be related toHomo rather than toPan orGorilla. However, this assumption is not supported by many other of their features. This paper briefly surveys the literature concerning craniodental comparisons of australopith species with those of bonobos, common chimps, humans and gorillas, adult and immature. It will be argued, albeit on fragmentary data, that the large australopiths of East Africa were in many instances anatomically and therefore possibly also evolutionarily nearer toGorilla than toPan orHomo, and the South African australopiths nearer toPan andHomo than toGorilla. An example of a possible evolutionary tree is provided. It is suggested that the evidence concerning the relation of the different australopithecines with humans, chimpanzees and gorillas should be re-evaluated.     

Relative orbitonasal overlap in african great apes and humans quantified by the automatic determination of horizontal and vertical lines of reference

The relative positions of the orbital and nasal openings in African apes and humans were studied by a new methodological approach based on the automatic determination, by image analysis techniques, of horizontal and vertical lines of reference. The material used consisted ofGorilla gorilla (38 males and 20 females),Pan troglodytes (19 males and 13 females), and modernHomo spaiens (51 males and 41 females). This allowed the relative positions of the orbital and nasal openings to be quantified by the determination of medio-lateral and vertical orbitonasal indices of overlap. In all the species studied, a medio-lateral orbitonasal overlap was systematically observed. This indicates that nasal breadth is always larger than interorbital distance. Medio-lateral overalp was greatest inGorilla, reduced inHomo, and intermediate inPan. By contrast, onlyHomo presents systematically a vertical overlap: a vertical overlap was sometimes observed inPan, but never inGorilla. Homo presented the greatest vertical overlap, andGorilla the least; the disposition inPan was intermediate. The interspectific study of the relationships between medio-lateral and vertical overlap inGorilla, Pan, andHomo demonstrated that an increase in veritical overlap was correlated with a decrease of medio-lateral overlap. Sexual dimorphism in orbitonasal relationships was systematically greatest inGorilla, and reduced inPan andHomo, this is also the case for the orbital, nasal, and orbitonasal parameters measured in this study. All these results provide interesting elements for understanding the morphological evolution of the middle face in hominoids.     

The Influence of Life History and Sexual Dimorphism on Entheseal Changes in Modern Humans and African Great Apes

Entheseal changes have been widely studied with regard to their correlation to biomechanical stress and their usefulness for biocultural reconstructions. However, anthropological and medical studies have demonstrated the marked influence of both age and sex on the development of these features. Studies of entheseal changes are mostly aimed in testing functional hypotheses and are mostly focused on modern humans, with few data available for non-human primates. The lack of comparative studies on the effect of age and sex on entheseal changes represent a gap in our understanding of the evolutionary basis of both development and degeneration of the human musculoskeletal system. The aim of the present work is to compare age trajectories and patterns of sexual dimorphism in entheseal changes between modern humans and African great apes. To this end we analyzed 23 postcranial entheses in a human contemporary identified skeletal collection (N = 484) and compared the results with those obtained from the analysis of Pan (N = 50) and Gorilla (N = 47) skeletal specimens. Results highlight taxon-specific age trajectories possibly linked to differences in life history schedules and phyletic relationships. Robusticity trajectories separate Pan and modern humans from Gorilla, whereas enthesopathic patterns are unique in modern humans and possibly linked to their extended potential lifespan. Comparisons between sexes evidence a decreasing dimorphism in robusticity from Gorilla, to modern humans to Pan, which is likely linked to the role played by size, lifespan and physical activity on robusticity development. The present study confirms previous hypotheses on the possible relevance of EC in the study of life history, pointing moreover to their usefulness in evolutionary studies.     

Baculum length and copulatory behavior in primates

The length of the baculum (os penis) was measured in 74 adult males representing 46 primate species. These data, and a review of previously published measurements, indicate that variation in baculum length among primates is related to taxonomic and behavioral differences. Thus, many New World monkeys have shorter bacula, relative to body weight, than Old World monkeys. The baculum is shorter in colobine monkeys than in cercopithecines. Among the great apes, reduction of the baculum is more pronounced in Pan and Gorilla than in Pongo. Very long bacula are found in some nocturnal prosimians (eg, Lorisidae) and also in Macaca arctoides. A comparison of baculum length relative to body weight was made in 34 species for which detailed information on copulatory behavi or was available. The presence of an elongated baculum was shown to correlate with copulatory patterns involving prolonged intromission and/or the maintenance of intromission during the postejaculatory interval (eg, Galago crassicaudatus, Loris tardigradus, M, arctoides). The evolutionary significance of these observations is discussed and it is suggeted that similar copulatory patterns may occur in species with elongated bacula (eg, Daubentonia, Perodicticus) for which behavioral data are lacking at present. The same hypothesis also applies to an extinct adapid primate which possessed a very large baculum.     

Brief communication: Ectocranial suture closure in Pongo: Pattern and phylogeny

Ectocranial suture fusion patterns have been shown to contain biological and phylogenetic information. Previously the patterns of Homo, Pan, and Gorilla have been described. These data reflect the phylogenetic relationships among these species. In this study, we applied similar methodology to Pongo to determine the suture synostosis progression of this genus, and to allow comparison to previously reported data on other large‐bodied hominoids. We hypothesized these data would strengthen the argument that suture synostosis patterns reflect the phylogeny of primate taxa. Results indicate that the synostosis of vault sutures in Pongo is similar to that reported for Gorilla (excluding Pan and Homo). However, the lateral‐anterior pattern of fusion, in which there is a strong superior to inferior pattern, for Pongo is unique among these species, reflecting its phylogenetic distinctness among great ape taxa. Am J Phys Anthropol, 2010. © 2010 Wiley‐Liss, Inc.     

Evolution of the human shoulder: some possible pathways

Osteometric data, apparently reflecting functional parameters of the shoulder in the Anthropoidea, have been examined by a combination of multivariate techniques in an attempt to define minimum pathways possibly followed in the evolution of the human shoulder. Principal components analysis has been used to gauge size-related shape effects. The combination of D² and canonical analysis has suggested that the shoulder in man is unlikely to have evolved (a) from one similar to that of any extant monkey whether arboreal or terrestrial, (b) from one similar to that of any terrestrial ape (like present-day Pan and Gorilla), or (c) from one similar to that of a highly specialised ricochetal armswinging ape (such as present day Hylobates and Symphalangus). The analyses suggest positively that the minimum evolutionary pathway may well have been from the shoulder of a totally arboreal ape, presumably genetically related to Pan and Gorilla, but functionally similar to that evolved in parallel in the highly arboreal orang-utan, Pongo. Information from fragmentary fossils (the scapula from Sterkfontein and the clavicle from Olduvai) supports these conclusions.     

Enamel hypoplasia in sympatric chimpanzee and gorilla

The prevalence of enamel hypoplasia in 229Pan andGorilla, from the Republic of Cameroon, is described. A substantially higher proportion of gorillas (76%) than chimpanzees (58%) was affected. The incidence of enamel hypoplasia was not a function of sex, body size, or pathology. A study of tooth formation, from radiographs of a further series of immature apes, indicated that the mandibular canine bore 99% of all information about hypoplasia events. In both species a marked regularity of hypoplastic grooving with an interval of about 11.4% of canine crown height was observed. This appears to reflect a semi-annual cycle of stress which is tentatively linked to the twice-yearly rainy season. Uniform spacing of hypoplastic grooves has been observed in a variety of fossil hominids. Readily observable hypoplastic time markers in the teeth have potential for disclosing growth rates in early Hominidae. This is considered important because of the profound significance which prolonged maturation and longevity characteristic of recent human beings have for the transmission of learned behavior and social bonding.     

Sexual dimorphism in the early Miocene species ofProconsul from the Kisingiri Formation of east Africa: A morphometric examination using multivariate statistics

This paper examines the pattern(s) of sexual dimorphism within the upper dentition ofProconsul specimens from the early Miocene of east Africa. These fossils are compared against the corresponding dentition ofPan troglodytes andGorilla gorilla using principal components and cluster analyses. This paper demonstrates that both sexes ofPan andGorilla are characterized by their own distinctive shape patterns. It is also demonstrated that someProconsul specimens examined here display a pattern that is dissimilar from otherProconsul specimens also examined. This suggests that at least two species ofProconsul may have to be recognized as having lived in this region during the early Miocene. The identification of distinct patterns withinProconsul also suggests that their overall shape and size range are more similar toPan than toGorilla.     

Interspecific and Ontogenetic Variation in Proximal Pedal Phalangeal Curvature of Great Apes (Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus)

Considerable attention has been devoted to understanding phalangeal curvature in primates, particularly with regard to locomotion. Previous work has found that increased phalangeal curvature may be indicative of increased grasping during suspensory and climbing behaviors, but the details of this relationship, particularly as regards feet, is still unclear. Using behavioral studies to predict an interspecific gradient of variation in pedal phalangeal curvature, I collected digital data from the third and fifth digit proximal pedal phalanges in adult Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus and calculated included angles of phalangeal curvature to assess the appropriateness of pooling digits within taxa and evaluate the association between variation in pedal phalangeal curvature and frequency of climbing behavior. I also used an ontogenetic sample of Pan troglodytes to evaluate the postnatal relationship between variation in phalangeal curvature and grasping behaviors. I found intraspecific variation in phalangeal curvature suggesting among-digit variation in grasping behaviors. Curvature of Pongo was significantly greater than of both Pan and Gorilla. In contrast, Pan was significantly more curved than Gorilla only in comparison of third digits. Ontogenetic decreases in pedal phalangeal curvature among Pan troglodytes accorded well with postnatal decreases in documented climbing frequency. These findings largely support earlier work regarding the association between arboreal grasping and phalangeal curvature, and provide a unique intraspecific analysis that illuminates a number of areas where our knowledge of the behavioral and biomechanical determinants of phalangeal curvature should be explored further, particularly with respect to the role of among-digit variation in phalangeal curvature.     

Geographic Variation in Nonmetric Dental Traits of the Deciduous Molars of Pan and Gorilla

Physical anthropologists often use nonmetric dental traits to trace the movement of human populations, but similar analysis of the teeth of nonhuman primates or the deciduous teeth is rare. Because nonmetric dental characteristics are manifestations of genetic differences among groups, they vary among geographically distant members of the same species and subspecies. We use 28 nonmetric dental traits in the deciduous molars to compare genetically and geographically distinct groups of extant African apes (Gorilla and Pan). Previous researchers have studied these traits in the adult or juvenile teeth of great apes and humans, and we score our observations according to established standards for hominins. We observe marked differences in trait frequencies between Gorilla and Pan, Pan troglodytes and P. paniscus, and two P. troglodytes subspecies but we find no significant differences between geographically isolated groups within the subspecies. Trait frequencies differ from those found in previous studies that contained fewer individuals. We find that the deciduous molars show similar variation to adult premolars and molars within Pan and Gorilla. This suggests that the deciduous dentition of these and other apes may contain diagnostic traits that are not currently in use.     

Palatine fenestrae,the orangutan and hominoid evolution

Although most mammals develop relatively large double anterior palatine fenestrae that patently communicate with the nasal cavity, four extant primates—Homo sapiens, Pongo, Pan andGorilla—do not. While these four have closed-down these foramenal structures,Homo sapiens andPongo are unique in forming a single foramen palatally. Among fossil taxa,Homo, Australopithecus, Sivapithecus (=Ramapithecus) andRudapithecus also develop a single foramen palatally. Dryopithecines, the presumed fossil apes, preserve the two patent fenestrae. In light of dental features that are considered diagnostically “hominid,” which are also found in the orangutan, it is suggested that this “ape,” rather thanPan, is phylogenetically closer toHomo.     

A contribution to tropical rain forest taphonomy: retrieval and documentation of chimpanzee remains from Kibale Forest, Uganda

The absence of Pan and Gorilla fossils from Africa has led some to suggest that African rain forests are not conducive to bone preservation. The absence of fossils is unfortunate as it hampers phylogenetic and socioecological interpretations on the divergence of the earliest hominids. For the most part, taphonomic studies have been restricted to cave and open country contexts. With this in mind, we have initiated a taphonomic project in a tropical rain forest, the Kibale Forest of western Uganda. In the course of bone gathering activities over the past 4 years, we have documented the retrieval of skeletal remains representing nine chimpanzees (Pan troglodytes schweinfurthii). Crania and mandibles are most commonly recovered, followed by elements of the axial skeleton, and finally, appendages. Vertical segregation of small compact bones can occur in areas with a soft substrate. Scavenging activity suggests the role of suids, but this has not been proven. Geochemical tests suggest that Kibale soils are neutral and may be conducive to bone preservation. Our independent preliminary data from bone weathering/survival experiments indicate that bones appear undamaged after several years and are able to accumulate on the forest floor. These results contrast with popular assumptions on the potential of African rain forests as potential fossil reservoirs.     

Understanding Language Evolution: Beyond Pan-Centrism

Language does not fossilize but this does not mean that the language's evolutionary timeline is lost forever. Great apes provide a window back in time on our last prelinguistic ancestor's communication and cognition. Phylogeny and cladistics implicitly conjure Pan (chimpanzees, bonobos) as a superior (often the only) model for language evolution compared with earlier diverging lineages, Gorilla and Pongo (orangutans). Here, in reviewing the literature, it is shown that Pan do not surpass other great apes along genetic, cognitive, ecologic, or vocal traits that are putatively paramount for language onset and evolution. Instead, revived herein is the idea that only by abandoning single-species models and learning about the variation among great apes, there might be a chance to retrieve lost fragments of the evolutionary timeline of language.     

Mechanical and spatial determinants of Paranthropus facial form

It is well documented in the anthropological literature that the distinctive morphology of the “robust” hominid facial skeleton reflects its dietary specialization. Rak (1983) has provided the most comprehensive evaluation of Paranthropus facial morphology and this important study concluded that bone strain generated during mastication was responsible for the scaling of measures of facial height and breadth. The present study evaluated Rak's analysis by examining the relationship between bizygomatic breadth and facial height in an ontogenetic series of Pan and Gorilla crania. Results of this analysis indicate that facial height and breadth dimensions were not mechanically scaled in the “robust” australopithecines. Structural analysis of African ape facial maturation was also used to examine alternative spatial methods of malar elongation in Paranthropus. It is concluded that the increased height of the malar region in these specimens is not related to either vertical expansion of the posterior facial skeleton or to expansion of the temporal fossa. Malar elongation is, however, consistent with a derived pattern of facial growth in crania possessing a thickened hard palate. © 1994 Wiley-Liss, Inc.     

Chromosomes and the origins of apes and australopithecins

Comparison of molecular data suggests that the higher apes (Gorilla, Pan) and humankind (Homo) are closely related and that they diverged from the common ancestor through two speciation events situated very closely together in time. Examination of the chromosomal formulas of the living species reveals a paradox in the distribution of mutated chromosomes which can only be resolved by a model of trichotomic diversification. This new model of divergence from the common ancestor is characterized by the transition from (1) a monotypic phase to (2) a polytypic phase of three sub-species — pre-gorilla, pre-chimpanzee and preaustralopithecine. The quadruped ancestors ofAustralopithecus appear to have been one of the three components of the common ancestor. The question is whetherramidus is an australopithecine or a pre-australopithecine representative of the common ancestor. The new model of diversification of the common ancestor is resituated in the paleogeographic and paleoclimatic context which, through the north-south pattern of extension of aridity, provides a coherent scenario for the formation of extant species and subspecies of theGorilla andPan genera.     

Comparative 3D quantitative analyses of trapeziometacarpal joint surface curvatures among living catarrhines and fossil hominins

Comparisons of joint surface curvature at the base of the thumb have long been made to discern differences among living and fossil primates in functional capabilities of the hand. However, the complex shape of this joint makes it difficult to quantify differences among taxa. The purpose of this study is to determine whether significant differences in curvature exist among selected catarrhine genera and to compare these genera with hominin¹ fossils in trapeziometacarpal curvature. Two 3D approaches are used to quantify curvatures of the trapezial and metacarpal joint surfaces: (1) stereophotogrammetry with nonuniform rational B‐spline (NURBS) calculation of joint curvature to compare modern humans with captive chimpanzees and (2) laser scanning with a quadric‐based calculation of curvature to compare modern humans and wild‐caught Pan, Gorilla, Pongo, and Papio. Both approaches show that Homo has significantly lower curvature of the joint surfaces than does Pan. The second approach shows that Gorilla has significantly more curvature than modern humans, while Pongo overlaps with humans and African apes. The surfaces in Papio are more cylindrical and flatter than in Homo. Australopithecus afarensis resembles African apes more than modern humans in curvatures, whereas the Homo habilis trapezial metacarpal surface is flatter than in all genera except Papio. Neandertals fall at one end of the modern human range of variation, with smaller dorsovolar curvature. Modern human topography appears to be derived relative to great apes and Australopithecus and contributes to the distinctive human morphology that facilitates forceful precision and power gripping, fundamental to human manipulative activities. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc. ¹ The term “hominin” refers to members of the tribe Hominini, which includes modern humans and fossil species that are related more closely to modern humans than to extant species of chimpanzees, Wood and Lonergan (2008). Hominins are in the family Hominidae with great apes.