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The origin of primates has had a long history of discussion and debate, with few ever considering the impact of the original body weight on subsequent primate adaptive radiations. Here, I attempt to reconstruct early primate evolution by considering the initial size of primates as well as the critical functional-adaptive events that had to occur prior to the early Eocene. Microcebus is often viewed as a living model, and thus 40-65 g might represent a practical ancestral weight for the origin of primates. I consider a smaller original body weight, likely 10-15 g in actual size, and I address the biological implications for shrew-sized primates by comparing the behavioral ecology of mouse lemurs, our smallest living primates, to another tiny-sized mammalian group, the shrews (Family Soricidae). Several behavioral and ecological characteristics are shared by shrews and mouse lemurs, and several mammalian trends are evident with decreased size. I suggest that a shrew-sized ancestral primate would have had high metabolic, reproductive, and predation rates, relatively low population densities, and a dispersed and solitary existence with a promiscuous mating system. Although small mammals like shrews provide insights concerning the ancestral size of primates, primate origins have always been tied to arboreality. I assess other potential arboreal models such as Ptilocercus and Caluromys. By combining all of this information, I try to sequence the events in a functional-adaptive series that had to occur before the early Eocene primate radiations. I suggest that all of these important adaptive events had to occur at a small body size below 50 g. KEY WORDS small body size; ecology; life-history traits; Soricidae; Microcebus; primate models; primate evolution

A tenet of evolutionary theory is that, within a species, phenotypic variability is inversely related to the intensity of stabilizing selection. A corollary is that a rudimentary or vestigial structure should be highly variable. This relationship between rudimentation and variability, however, may simply be part of a continuum, as several studies have shown that variability and size of a structure are inversely related. This study tests whether the first metacarpal (MC1) in Ateles geoffroyi and Colobus guereza and the second metacarpal (MC2) in Perodicticus potto are highly variable in their lengths relative to their other metapodials. The former two species have rudimentary thumbs, and the latter species has a rudimentary index finger. Fourteen other species of primates are included in the comparison. The results show that MC1 in A. geoffroyi and C. guereza and MC2 in P. potto are the relatively shortest first and second metapodials, respectively, in this sample of primates. However, an intraspecific analysis shows that neither MC1 in A. geoffroyi and C. guereza nor MC2 in P. potto is significantly more variable than the other metapodials. Nevertheless, an interspecific analysis shows that MC1 in A. geoffroyi and C. guereza is relatively the most variable among the first metapodials (i.e., MC1 and first metatarsal) in this study. MC2 in P. potto, however, is of relatively low variability compared with the other primates. These contrasting results are interpreted in terms of the developmental and evolutionary biology of digits. Am J Phys Anthropol 117:195-208, 2002. KEY WORDS Hox gene; index finger; metacarpal; metatarsal; rudiment; thumb; vestige

Fused symphyses, which evolved independently in several mammalian taxa, including anthropoids, are stiffer and stronger than unfused symphyses. This paper tests the hypothesis that orientations of tooth movements during occlusion are the primary basis for variations in symphyseal fusion. Mammals whose teeth have primarily dorsally oriented occlusal trajectories and/or rotate their mandibles during occlusion will not benefit from symphyseal fusion because it prevents independent mandibular movements and because unfused symphyses transfer dorsally oriented forces with equal efficiency; mammals with predominantly transverse power strokes are predicted to benefit from symphyseal fusion or greatly restricted mediolateral movement at the symphysis in order to increase force transfer efficiency across the symphysis in the transverse plane. These hypotheses are tested with comparative data on symphyseal and occlusal morphology in several mammals, and with kinematic and EMG analyses of mastication in opossums (Didelphis virginiana) and goats (Capra hircus) that are compared with published data on chewing in primates. Among mammals, symphyseal fusion or a morphology that greatly restricts movement correlates significantly with occlusal orientation: species with more transversely oriented occlusal planes tend to have fused symphyses. The ratio of working- to balancing-side adductor muscle force in goats and opossums is close to 1:1, as in macaques, but goats and opossums have mandibles that rotate independently during occlusion, and have predominantly vertically oriented tooth movements during the power stroke. Symphyseal fusion is therefore most likely an adaptation for increasing the efficiency of transfer of transversely oriented occlusal forces in mammals whose mandibles do not rotate independently during the power stroke. Keywords: symphysis; mammals; primates; electromyograms; mandible; mastication

The purpose of this study is to test various hypotheses about balancing-side jaw muscle recruitment patterns during mastication, with a major focus on testing the hypothesis that symphyseal fusion in anthropoids is due mainly to vertically- and/or transversely-directed jaw muscle forces. Furthermore, as the balancing-side deep masseter has been shown to play an important role in wishboning of the macaque mandibular symphysis, we test the hypothesis that primates possessing a highly mobile mandibular symphysis do not exhibit the balancing-side deep masseter firing pattern that causes wishboning of the anthropoid mandible. Finally, we also test the hypothesis that balancing-side muscle recruitment patterns are importantly related to allometric constraints associated with the evolution of increasing body size. Electromyographic (EMG) activity of the left and right superficial and deep masseters were recorded and analyzed in baboons, macaques, owl monkeys, and thick-tailed galagos. The masseter was chosen for analysis because in the frontal projection its superficial portion exerts force primarily in the vertical (dorsoventral) direction, whereas its deep portion has a relatively larger component of force in the transverse direction. The symphyseal fusion-muscle recruitment hypothesis predicts that unlike anthropoids, galagos develop bite force with relatively little contribution from their balancing-side jaw muscles. Thus, compared to galagos, anthropoids recruit a larger percentage of force from their balancing-side muscles. If true, this means that during forceful mastication, galagos should have working-side/balancing-side (W/B) EMG ratios that are relatively large, whereas anthropoids should have W/B ratios that are relatively small. The EMG data indicate that galagos do indeed have the largest average W/B ratios for both the superficial and deep masseters (2.2 and 4.4, respectively). Among the anthropoids, the average W/B ratios for the superficial and deep masseters are 1.9 and 1.0 for baboons, 1.4 and 1.0 for macaques, and both values are 1.4 for owl monkeys. Of these ratios, however, the only significant difference between thick-tailed galagos and anthropoids are those associated with the deep masseter. Furthermore, the analysis of masseter firing patterns indicates that whereas baboons, macaques and owl monkeys exhibit the deep masseter firing pattern associated with wishboning of the macaque mandibular symphysis, galagos do not exhibit this firing pattern. The allometric constraint-muscle recruitment hypothesis predicts that larger primates must recruit relatively larger amounts of balancing-side muscle force so as to develop equivalent amounts of bite force. Operationally this means that during forceful mastication, the W/B EMG ratios for the superficial and deep masseters should be negatively correlated with body size. Our analysis clearly refutes this hypothesis. As already noted, the average W/B ratios for both the superficial and deep masseter are largest in thick-tailed galagos, and not, as predicted by the allometric constraint hypothesis, in owl monkeys, an anthropoid whose body size is smaller than that of thick-tailed galagos. Our analysis also indicates that owl monkeys have W/B ratios that are small and more similar to those of the much larger-sized baboons and macaques. Thus, both the analysis of the W/B EMG ratios and the muscle firing pattern data support the hypothesis that symphyseal fusion and transversely-directed muscle force in anthropoids are functionally linked. This in turn supports the hypothesis that the evolution of symphyseal fusion in anthropoids is an adaptation to strengthen the symphysis so as to counter increased wishboning stress during forceful unilateral mastication. In contrast, the W/B EMG ratios provide no (or arguably weak) support for the hypothesis that symphyseal fusion and vertically-directed muscle force are functionally linked, and the data clearly refute the hypothesis that balancing-side jaw-muscle recruitment patterns are influenced by allometric factors associated with the evolution of increasing body size. Keywords: symphyseal fusion; electromyography; wishboning; jaw-adductor muscle force; mastication; primates

Among the characteristics that are thought to set primate quadrupedal locomotion apart from that of nonprimate mammals are a more protracted limb posture and larger limb angular excursion. However, kinematic aspects of primate or nonprimate quadrupedal locomotion have been documented in only a handful of species, and more widely for the hind than the forelimb. This study presents data on arm (humerus) and forelimb posture during walking for 102 species of mammals, including 53 nonhuman primates and 49 nonprimate mammals. The results demonstrate that primates uniformly display a more protracted arm and forelimb at hand touchdown of a step than nearly all other mammals. Although primates tend to end a step with a less retracted humerus, their total humeral or forelimb angular excursion exceeds that of other mammals. It is suggested that these features are components of functional adaptations to locomotion in an arboreal habitat, using clawless, grasping extremities.

The pulvinar nuclei of the thalamus are proportionately larger in higher mammals, particularly in primates, and account for a quarter of the total mass. Traditionally, these nuclei have been divided into oral (somatosensory), superior and inferior (both visual) and medial (visual, multi-sensory) divisions. With reciprocal connections to vast areas of cerebral cortex, and input from the colliculus and retina, they occupy an analogous position in the extra-striate visual system to the lateral geniculate nucleus in the primary visual pathway, but deal with higher-order visual and visuomotor transduction. With a renewed recent interest in this thalamic nuclear collection, and growth in our knowledge of the cortex with which it communicates, perhaps the time is right to look to new dimensions in the pulvinar code.

Two very small late Eocene anthropoid primates, Catopithecus browni and Proteopithecus sylviae, from Fayum, Egypt show evidence of substantial sexual dimorphism in canine teeth. The degree of dimorphism suggests that these early anthropoids lived in social groups with a polygynous mating system and intense male-male competition. Catopithecus and Proteopithecus are smaller in estimated body size than any living primates showing canine dimorphism. The origin of canine dimorphism and polygyny in anthropoids was not associated with the evolution of large body size.

Most functional analyses of primate tooth form have been limited to linear or area measurements. Such studies have offered but a limited glimpse at differences in occlusal relief among taxa. Such differences in dental topography may relate to tooth function and, so, have considerable implications for the inference of diet from fossil teeth. In this article, we describe a technique to model and compare primate molars in three dimensions using Geographic Resources Analysis Support System (GRASS) software. We examine unworn lower second molars of three extant hominoids with known differences in diet (Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus), and two fossil forms, (Afropithecus turkanesis and Dryopithecus laietanus). First, we obtained approximately 400 landmarks on the occlusal surfaces of each tooth using an electromagnetic digitizer. Raster 'terrain models' of occlusal surfaces were then created by interpolation of the coordinate data. We used GRASS terrain analysis automated techniques to quantify the volumes and slopes of individual cusps. We also used the GRASS watershed technique to identify the volume of liquid that would accumulate in each tooth's basin (a measure of basin area), and the directions and intensity of drainage over the occlusal surface. In sum, GRASS shows considerable potential for the characterization and comparison of tooth surfaces. Furthermore, techniques described here are not limited to the study of teeth, but may be broadly applicable to studies of skulls, joints, and other biological structures. KEY WORDS GIS; GRASS; primate dental morphology

The hypothesis that the vomeronasal organ has an important functional relationship with, and led to the evolution of, the prosimian toothcomb has not been well tested. This paper examines the diversity of anatomical strepsirrhinism across several mammalian taxa to determine if fossil and living strepsirrhine primates exhibit any derived characters that may highlight the functional link between the vomeronasal organ and the toothcomb, and to examine the potential importance of anatomical strepsirrhinism to toothcomb origins. Results indicate that extant gregarious lemuri-forms are derived in having a relatively wide interincisal gap, providing an unobstructed line of communication between the vomeronasal organ and anterior rostral structures such as the toothcomb. This finding is consistent with the proposal that anatomical strepsirrhinism is functionally related to use of the toothcomb in grooming. However, the importance of the vomeronasal organ to toothcomb origins is less clear. If the morphology of adapiforms and non-gregarious lemuriforms is representative of the morphology of basal lemuriforms, then it can be inferred that early lemuriforms did not possess the wide-gap autapomorphy; hence, anatomical evidence discussed here cannot be used to rule out non-social hypotheses of toothcomb origins. KEY WORDS rostrum; vomeronasal organ; grooming; primates

Atelines are of particular interest to primate evolutionary studies because they converge with hominoids in postcranial anatomy, including the vertebral column. Currently, our understanding of ateline vertebral morphology is limited to mainly qualitative descriptions and functional interpretations based on general categories of positional behavior. Even less is known about the vertebrae of other platyrrhines. This study more closely examines vertebral form and function in atelines and cebines by combining direct field observations of axial postures and movements, assessments of spinal loading regimes, and a detailed vertebral morphometric analysis. Field observations (Corcovado, Costa Rica) on Ateles geoffroyi, Alouatta palliata, Cebus capucinus, and Saimiri oerstedii were quantified in conjunction with a morphometric analysis of ateline and cebine lumbar vertebrae. Hylobates was also included for comparison. Compared to Cebus and Saimiri, atelines engage more frequently in postures and locomotor behaviors that induce pronounced bending loads on the spine. All atelines share lumbar adaptations for resisting bending, including ventrodorsally elongated vertebral bodies and perpendicularly oriented transverse processes. Among atelines, lumbar region lengths and vertebral bodies are shortest in Ateles and Brachyteles, longest in Alouatta (resembling Cebus), and intermediate in Lagothrix. Compared to Cebus and all atelines, Saimiri has a relatively longer lumbar region, longer and less ventrodorsally expanded vertebral bodies, and more ventrally oriented transverse processes. These features accentuate bending loads, but increase the sagittal flexibility required for leaping. Vertebral convergence between hylobatids and atelines is more readily interpretable as a product of shared spinal loading patterns than shared positional behaviors. KEY WORDS platyrrhine; lumbar; locomotion; posture

Recent discovery of crania, dentitions, and postcrania of a primitive anthropoidean primate, Proteopithecus sylviae, at the late Eocene L-41 quarry in the Fayum, Egypt, provides evidence of a new taxonomic family of early African higher primates, the Proteopithecidae. This family could be part of the basal radiation that produced the New World platyrrhine primates, or it could be unrelated to any subsequent lineages. Although no larger than a small callitrichid or a dwarf lemur, this tiny primate already possessed many of the derived features of later anthropoids and was a diurnal and probably dimorphic species. In dental formula and other dental proportions, as well as in known postcranial features, Proteopithecus more nearly resembles platyrrhines than does any other Old World higher primate. The small size of the Proteopithecus cranium demonstrates that the defining cranial characteristics of Anthropoidea did not arise as a consequence of an increase in size during derivation from earlier prosimians.

Our thinking on the cortical organization of primate memory is undergoing a copernican change, from a neuropsychology that localizes different memories in different areas to one that views memory as a distributed property of cortical systems. We are shifting our focus from 'systems of memory' to the memory of systems. The same cortical systems that serve us to perceive and move in the world serve us to remember it. Our memories are networks of interconnected cortical neurons, formed by association, that contain our experiences in their connectional structure. Perceptual and motor memory networks are hierarchically organized in post-rolandic and pre-rolandic neocortex, respectively. Recall, recognition and working memory consist largely in their reactivation, also by association.

Seven measurements in the cerebellar complex were completed on 45 individuals, including 26 species of anthropoids from Stephan's collection. These included 12 species of New World monkeys, 10 species of Old World monkeys, and Hylobates, Gorilla, Pan, and humans. The measurements were the volume of medial (fastigial) (CM), interpositus (globose and emboliform) (CI), and lateral (dentate) (CL) cerebellar nuclei, ventral pons (VPo), inferior olivary principal (OLIPr), and accessory (OLIAc) nuclei and vestibular nuclear complex (VES). The relative size of each nucleus was expressed in size indices based upon the allometric line obtained by the reduced major axis analysis. The indices of three cerebellar nuclei reflect the relative size of three longitudinal zones of the cerebellum. The cerebellar hemisphere-lateralis zone is represented by the CL indices, the vermis-medialis zone by the CM indices, and the pars intermedius-interpositus zone by the CI indices. The results show that the VPo and OLIPr indices are closely related to the CL indices. This lateral zone group of nuclei is the most progressively developed in humans, whereas the CM, CI, OLIAc, and VES are independent of the developmental trend manifest by the lateral zone group of nuclei. The indices are discussed in relation to the predominant locomotor pattern exhibited by a species. The size indices of arboreal quadrupeds show a development of all nuclei in the cerebellar complex. This is interpreted as indicating that arboreal monkeys live in complicated, discontinuous, three-dimensional space and need exceptional cerebellar capacity for each pattern of locomotion and positional behavior. Progressive development of the lateral zone group of nuclei only compared to other nuclei was recognizable in humans. This development is considered to be related not to bipedalism, but to versatile and coordinated finger movement, resulting after bipedalism was established. This cerebellar reorganization is also a prerequisite (Leiner et al. [1993] TINS 16: 444-447) for the evolution of human language. The differences between size indices of the nuclei of Macaca (=pronograde primate) and Ateles (=antipronograde one) are compared in relation to their vertical climbing kinesiological data. KEY WORDS cerebellar complex; morphometry; locomotor types; anthropoids; Stephan's collection

Most studies of microscopic wear on non-human primate teeth have focused on the occlusal surfaces of molars. Recent analyses of the buccal surfaces of human cheek teeth have demonstrated an association between diet and dental microwear on the these surfaces as well. In the current study, we examine microwear on both the buccal and lingual surfaces of non-human primate molars to assess the potential of these surfaces to reveal information concerning anthropoid feeding behaviors. We compare frequency of microwear occurrence in 12 extant and 11 fossil anthropoid species. Among the living primates, the occurrence of microwear on non-occlusal surfaces appears to relate to both diet and degree of terrestriality. The implications of this research for the inference of feeding behaviors and substrate use in fossil cercopithecoids are discussed.

Studies of the dynamics of locomotor performances depend on knowledge of the distribution of body mass within and between limb segments. However, these data are difficult to derive. Segment mass properties have generally been estimated by modelling limbs as truncated cones, but this approach fails to take into account that some segments are of elliptical, not circular, cross section; and further, the profiles of real segments are generally curved. Thus, they are more appropriately modelled as solids of revolution, described by the rotation in space of convex or concave curves, and the possibility of an elliptical cross section needs to be taken into account. In this project we have set out to develop a general geometric model which can take these factors into account, and permit segment inertial properties to be derived from cadavers by segmentation, and from living individuals using linear external measurements. We present a model which may be described by up to four parameters, depending on the profile and serial cross section (circular or ellipsoidal) of the individual segments. The parameters are obtained from cadavers using a simplified complex-pendulum technique, and from intact specimens by calculation from measurements of segment diameters and lengths. From the parameters, the center of mass, moments of inertia, and radii of gyration may be derived, using simultaneous equations. Inertial properties of the body segments of four Pan troglodytes and a single Pongo were determined, and contrasted to comparable findings for humans. Using our approach, the mass distribution characteristics of any individual or species may be represented by a rigid-link segment model or 'android.' If this is made to move according to motion functions derived from a real performance of the individual represented, we show that recordings of resulting ground reaction forces may be quite closely simulated by predictive dynamic modelling. KEY WORDS Locomotion, Biomechanics, Computer Modelling, Inertia, Segment masses

Tactile information about an object in contact with the skin surface is contained in the spatio-temporal load distribution on the skin, the corresponding stresses and strains at mechanosensitive receptor locations within the skin, and the associated pattern of electrical impulses produced by the receptor population. At present, although the responses of the receptors to known stimuli can be recorded, no experimental techniques exist to observe either the load distribution on the skin or the corresponding stress-state at the receptor locations. In this paper, the role of mechanics in the neural coding of tactile information is investigated using simple models of the primate fingertip. Four models that range in geometry from a semi-infinite medium to a cylindrical finger with a rigid bone, and composed of linear elastic media, are analyzed under plane strain conditions using the finite element method. The results show that the model geometry has a significant influence on the surface load distribution as well as the subsurface stress and strain fields for a given mechanical stimulus. The elastic medium acts like a spatial low pass filter with the property that deeper the receptor location, the more blurred the tactile information. None of the models predicted the experimentally observed surface deflection profiles under line loads as closely as a simple heterogeneous waterbed model that treated the fingerpad as a membrane enclosing an incompressible fluid (Srinivasan, 1989). This waterbed model however, predicted a uniform state of stress inside the fingertip and thus failed to explain the spatial variations observed in the neural response. For the cylindrical model indented by rectangular gratings, the maximum compressive strain and strain energy density at typicol receptor locations emerged as the two strain measures that were directly related to the electrophysiologically recorded response rate of slowly adapting type I (SAI) mechanoreceptors. Strain energy density is a better candidate to be the relevant stimulus for SAIs, since it is a scalar that is invariant with respect to receptor orientations and is a direct measure of the distortion of the receptor caused by the loads imposed on the skin.

Size variation in African apes (Gorilla gorilla [gorilla], Pan paniscus [pygmy chimpanzee], and Pan troglodytes ['common' chimpanzee]) is substantial, both within and between species. We investigate the possible evolutionary significance of this variation through an analysis of the ontogeny of size variation in this group. In addition, we highlight possible areas of future endocrinological research, and evaluate recently proposed alternative models that attempt to account for ontogenetic variation in apes. The present study shows that intergeneric variation in size is largely a consequence of differences among species in the rate of body weight growth. Interspecific size variation in Pan is a product of both rate and duration differences in growth. The ontogenetic bases of sexual dimorphism vary in this group. Dimorphism is largely a result of sex differences in the duration of body weight growth in gorillas and pygmy chimpanzees, but results from differences in the rate of growth in common chimpanzees. Ontogenetic analyses largely confirm earlier interpretations, but with better data and methods. The great degree of ontogenetic variation within and among these species, especially in the timing and magnitude of 'pubertal' growth spurts, implies that studies of endocrine growth control in African apes could be a productive line of future research. We also suggest that ontogenetic variation can be understood with respect to ecological risks. Growth rates seem to be negatively correlated with ecological risk in African apes, suggesting links between ontogenetic patterns and social and ecological variables. High growth rates in gorillas compared to Pan are most consistent with this model. Variation between chimpanzees and pygmy chimpanzees (especially females) also seem to fit predictions of this model. KEY WORDS Primates, Growth and development, Growth spurt

A recurrent theme in the organization of vertebrate visual cortex is that of receptive fields with an associated 'silent' opponency component. In the middle temporal area (area MT), a cortical visual area involved in the analysis of retinal motion in primates, this opponency appears in the form of a region outside the classical receptive field (CRF) that in itself gives no response but suppresses responses to motion evoked within the CRF. This antagonistic motion surround has been described as very large and symmetrically arrayed around the CRF. On the basis of this view, the primary function of the surround has long been thought to consist of simple figure-ground segregation based on movement. We have made use of small stimulus patches to map the form and extent of the surround and find evidence that the surround inhibition of many MT cells is in fact confined to restricted regions on one side or on opposite sides of the CRF. Such regions endow Ml cells with the ability to make local-to-local motion comparisons, capable of extracting more complex features from the visual environment, and as such, may be better viewed as intrinsic parts of the receptive field, rather than as separate entities responsible for local-to-global comparisons.

The study of muscle function in nonhuman primates through the technique of electromyography (EMG) has facilitated the identification of specific functional roles for muscles in particular behaviors. This has led to a more complete understanding of the biomechanics of certain regions of the musculoskeletal system, and should facilitate our ability to identify morphological features useful in the functional interpretation of fossil material. The current paper represents one such investigation of a new set of morphometric characters of the scapula and proximal humerus suggested by EMG analyses of shoulder muscle function. A set of new metric variables were examined on the scapulae and proximal humeri of 25 species of extant anthropoid primates, as well as on casts of scapulae and humeri of three fossil primate taxa. The variables are primarily related to the line of action and attachments of the rotator cuff muscles. The position of the scapular spine, the degree of lateral expansion of the subscapular fossa, the size and shape of the subscapularis insertion facet on the lesser tubercle, and the orientation of the infraspinatus insertion facet on the greater tubercle all appear to successfully sort the extant taxa into locomotor groups. Their appearance on the fossil specimens generally supports previous functional interpretations of each taxon's locomotor abilities based on a variety of other characters, suggesting that these traits are equally applicable to fossil material. KEY WORDS Shoulder, Electromyography, Functional morphology, Biomechanics

It has been generally assumed and theoretically argued that the curvature of finger and toe bones seen in some nonhuman primates is associated with cheiridial use in an arboreal setting. Assessment of such curvature in fossil primates has been used to infer the positional behavior of these animals. Several methods of quantifying curvature of bones have been proposed. The measure most commonly applied to phalanges is that of included angle, but this has come under some criticism. We consider various other approaches for quantifying phalangeal curvature, demonstrating that some are equivalent to use of included angle, but that one - normalized curvature moment arm (NCMA) - represents a true alternative. A comparison of NCMA to included angle, both calculated on manual and pedal proximal phalanges of humans, apes, some monkeys, and the Hadar fossils, revealed that these two different measures of curvature are highly correlated and result in very similar distributional patterns. KEY WORDS: Proximal phalanges, Primates, Curvature, Hand, Foot

Systematic analysis of the cranium of Plesiopithecus teras primate from the L-41 site in Eocene deposits of Egypt reveals that Plesiopithecus is prosimian and the morphology of its mandibular molars is homologous to that of archaic Anthropoidea members. Plesiopithecus contains a postorbital bar and constitutes a new family and superfamily close to the toothcomb prosimian's family. The procumbent tooth of Plesiopithecus resembles the canine or lateral incisor of the prosimian toothcomb.

Morphological features of the jaws and teeth are examined in eight species of platyrrhine monkeys that coexist in the Suriname rainforest. Z-scores calculated from geometric predictions for several features of the feeding apparatus thought to have some functional significance (e.g., tooth dimensions, jaw robusticity, leverage of primary jaw elevators) are compared to a profile of the naturalistic dietary behavior of these species (i.e., proportions of fruit mesocarp, seeds, leaves, and fauna eaten). Several features are found exclusively in those platyrrhines whose dietary preferences are the most limited. Such specializations appear to be associated with a particular protein source exploited by a species to supplement a largely frugivorous diet. Ateles paniscus, which feeds primarily on the mesocarp of ripe fruit, has an adaptive morphology that emphasizes broad incisors. Chiropotes satanas (and to a slightly lesser extent, Pithecia pithecia) is a frugivore/seed predator with large upper and lower canines and a robust mandible. The frugivore/folivore Alouatta seniculus has a relatively large total molar area and effective mandibular condyle height. In all four of these strictly vegetarian species, the leverage of the masseter muscle is greater than that of temporalis. Of the omnivorous species, Cebus apella and C. nigrivittatus exploit both fauna and seeds for protein and exhibit an array of many of the above features, such as large teeth and thick mandibles. Saimiri sciureus, not particularly known for seed predation, departs from Cebus in having less robust canines and a more gracile mandible. All three cebid omnivores have a temporalis with greater leverage than the masseter, indicating a requirement for resisting anteriorly directed forces, for example, using the jaws for vigorous foraging. The lack of any enlarged features, other than incisors, in the omnivorous Saguinus midas may be attributable to the functional constraints of small body size. Because the small size of the gape limits the size of the food parcel ingested, a requirement to enlarge other dentomandibular structures for trituration is alleviated.

Despite the extensive electromyographic research that has addressed limb muscle function during primate quadrupedalism, the role of the back muscles in this locomotor behavior has remained undocumented. We report here the results of an electromyographic (EMG) analysis of three intrinsic back muscles (multifidus, longissimus, and iliocostalis) in the baboon (Papio anubis), chimpanzee (Pan troglodytes), and orangutan (Pongo pygmaeus) during quadrupedal walking. The recruitment patterns of these three back muscles are compared to those reported for the same muscles during nonprimate quadrupedalism. In addition, the function of the back muscles during quadrupedalism and bipedalism in the two hominoids is compared. Results indicate that the back muscles restrict trunk movements during quadrupedalism by contracting with the touchdown of one or both feet, with more consistent activity associated with touchdown of the contralateral foot. Moreover, despite reported differences in their gait preferences and forelimb muscle EMG patterns, primates and nonprimate mammals recruit their back muscles in an essentially similar fashion during quadrupedal walking. These quadrupedal EMG patterns also resemble those reported for chimpanzees, gibbons and humans (but not orangutans) walking bipedally. The fundamental similarity in back muscle function across species and locomotor behaviors is consistent with other data pointing to conservatism in the evolution of the neural control of tetrapod limb movement, but does not preclude the suggestion (based on forelimb muscle EMG and spinal lesion studies) that some aspects of primate neural circuitry are unique.

A small bistratified cell that is a non-midget ganglion cell, receives excitory signals from the S cones or the 'blue-on' cell and conveys them to the brain. S cone photoreceptors are sensitive to short wavelengths. This 'blue-on' pathway could be separated anatomically at the lateral geniculate nucleus level.

Sixty years ago, Adolph Schultz attempted to collect all available information on the ages at which primates erupt their teeth. His search recovered complete data for only two nonhuman primate species, both macaques (Schultz, 1935). Although dozens of studies of individual primate species have appeared since, many remain scattered in the primary literature. The present study takes another step towards the task that Schultz began by gathering together all data on ages of tooth eruption for every primate species that could be located, from published and unpublished sources. After adding new data, at least one datum on tooth eruption can be described for 46 species representing all primate families. Data for 36 species are presented in an extended format with recommendations to help standardize future data collection and reporting. The compendium makes it possible to describe, for the first time, the basic outline of the eruption of teeth of primates from birth to adulthood. A preliminary analysis finds: many primates are born with teeth already erupted and only great apes and humans typically remain toothless after a month of postnatal life. Eruption of the dentition is tightly integrated overall, but the first few teeth to erupt give unique information about species life history, probably reflecting infant precociality. Mean age of tooth eruption is strongly related to size, measured as mean adult body weight (r = 0.72-0.92) or mean adult brain weight (r = 0.82-0.97). Important gaps remain in our knowledge of great apes, gibbons, colobus monkeys, folivorous cebids, and lorises. For many species, day-of-birth records or brief longitudinal studies extending only weeks or months could provide extremely valuable life-history data. Overall, eruption of teeth offers an excellent method to gauge both the maturation of individuals and to compare the life histories of species. KEY WORDS Dental development, Tooth emergence, Brain weight, Body weight

While studies of canine dimorphism in primates are common, only a few have examined canine tooth size independently within each sex. Recently, Greenfield and Washburn (Am. J. Phys. Anthropol. 84:17-34, 1991) proposed that there are two types of male canines which reflect different allometric scaling patterns of canine crown height against canine occlusal dimensions. They also suggest that proportional canine shape, measured as canine crown height (or projection) relative to the occlusal dimensions, provides an estimate of the canine's function as a weapon, though they provide no test of this hypothesis. This analysis critically examines the claim that there are two types of male canines among anthropoids. It then tests the hypothesis that relative male canine size (measured against body weight) and proportional canine shape are related to estimates of intermale competition, diet, and substrate (used as a surrogate measure of predation pressure). While there is strong taxonomic variation in canine size and shape among male anthropoids, no evidence is found for two discrete canine types. Rather, within families and subfamilies, canine dimensions scale isometrically against body weight and against each other, with a continuum of canine shapes among different taxa. While variation in male canine size is associated with intermale competition and substrate, even when taxonomic variation is controlled, variation in proportional canine shape is not. Neither canine size nor shape are generally associated with variation in diet.

A highly significant correlation is demonstrated between the forward inclination of the superficial masseter muscle and the forward tilt of molar teeth in the sagittal plane, conforming to the posterior end of the curve of Spee. The skulls studied included New and Old World monkeys, anthropoid apes, man, and a selection of other mammals. There was a wide variation between the angles measured in different animals (from 54 degrees to 115 degrees). The tilt of the curve of Spee increases the crush/shear ratio of the force produced on food between the posterior molars. The parallel tilt of superficial masseter maximizes the efficiency with which this muscle contributes to the crush component of the bite force in the sagittal plane.

Numerous hypotheses explaining interspecific differences in the degree of basicranial flexion have been presented. Several authors have argued that an increase in relative brain size results in a spatial packing problem that is resolved by flexing the basicranium. Others attribute differences in the degree of basicranial flexion to different postural behaviors, suggesting that more orthograde animals require a ventrally flexed pre-sella basicranium in order to maintain the eyes in a correct forward-facing orientation. Less specific claims are made for a relationship between the degree of basicranial flexion and facial orientation. In order to evaluate these hypotheses, the degree of basicranial flexion (cranial base angle), palate orientation, and orbital axis orientation were measured from lateral radiographs of 68 primate species and combined with linear and volumetric measures as well as data on the size of the neocortex and telencephalon. Bivariate correlation and partial correlation analyses at several taxonomic levels revealed that, within haplorhines, the cranial base angle decreases with increasing neurocranial volume relative to basicranial length and is positively correlated with angles of facial kyphosis and orbital axis orientation. Strepsirhines show no significant correlations between the cranial base angle and any of the variables examined. It is argued that prior orbital approximation in the ancestral haplorhine integrated the medial orbital walls and pre-sella basicranium into a single structural network such that changes in the orientation of one necessarily affect the other. Gould's ('Ontogeny and Phylogeny.' Cambridge: Belknap Press, 1977) hypothesis, that the highly flexed basicranium of Homo may be due to a combination of a large brain and a relatively short basicranium, is corroborated.

Since Mivart (1865), Cacajao, Chiropotes, and Pithecia have been grouped into a single taxon, which he called the subfamily Pitheciinae but which I, following Rosenberger (this issue), refer to as the living members of the tribe Pitheciini. While few today doubt the association of these three living genera, not all would place them together with Aotus and Callicebus in the subfamily Pitheciinae. This is an attempt to sort out the behavioral and morphological features of feeding and dental morphology in these taxa. Extant members of the tribe Pitheciini are adapted for sclerocarpic foraging, morphological evidence for which is found in the fossils of Soriacebus and Cebupithecia; Sclerocarpic foraging in living pitheciins is a two-stage process of seed predation involving 1) specialized features of the anterior dentition that allow removal of a hard pericarp that protects a seed or seeds, followed by 2) mastication by the posterior dentition having low cusp relief to triturate nutritious seeds of a relatively soft and uniformly pliable consistency. The dentitions of fossil pitheciins, Soriacebus and Cebupithecia, demonstrate that the hypertrophy of lower incisors plus the robustness and flaring of the canine precede development of low cusp relief on molars and premolars in the evolution of morphological features associated with sclerocarpic foraging. Features of sclerocarpic foraging are found less uniformly in the other two pitheciines, Callicebus and Aotus.

In addition to being frugivorous, Cebus and Saimiri stand out among the New World primates of similar body size in being heavily dependent on animal matter for protein (faunivory). A detailed description of the morphology and behavior of the two genera is presented with the object of evaluating the interaction and respective contributions of morphological and behavioral adaptations to foraging patterns. Our conclusions include the following: First, body size is extremely important in explaining the observed variation in diet. Second, the emphasis on faunivory is facilitated more by behavioral than by morphological specialization. Third, whatever morphological specializations are present, particularly in Cebus, are probably favored by diet at the most food-depauperate time of year. Fourth, although morphology may well reveal what a primate may potentially eat, to map this potential onto actual diet requires a detailed knowledge of its natural ecosystem. Finally, we consider whether the behavioral data support the tenuous morphological evidence for grouping Cebus and Saimiri within the clade Cebinae.

The division of the primate cortical visual system into dorsal and ventral streams with limited cross-talk was confirmed using an optimization approach. This approach analyzed various parcellation schemes to determine how the cortical regions correspond to the configuration of points. Organization of the primate visual cortex is also marked by streams that are hierarchical and meet in area 46 and at the superior temporal polysensory area and by the innervation of adjacent areas.

A recent study has indicated that heritage may be an important component in explanations of interspecies variation in male anthropoid maxillary canines. To further test this hypothesis, comparative data for the maxillary canine's occlusal partner, the honing mandibular premolar, are presented. Relative to body mass, measurements of the honing premolar--length of the honing facet, mesiodistal length, and buccolingual breadth and shape (as expressed by the ratio of length to breadth)--show a similar but stronger heritage component than measurements of the maxillary canine. Results indicate that canine variation among male anthropoids has not yet been explained and that quantitative analyses of this issue will necessarily require a methodological approach which incorporates heritage as a factor.

Pelvic diameters (both anteroposterior [AP] and transverse [TR]) were investigated in a series of anthropoid primates. The ratio of diameters (AP/TR) in each of three pelvic planes (inlet, midpelvis, and outlet) was calculated. In addition to the above, the length of the iliac, pubic, and ischial axes and the angles between these axes were determined. The AP/TR ratio at the pelvic inlet is (reported in millimeters, [+ or -] SD, unless otherwise specified) 1.81 [+ or -] 0.27 in New World monkeys (Cebidae) and Macaca mulatta; 1.53 [+ or -] 0.17 in hylobatids and pongids; 0.87 [+ or -] 0.08 in Homo sapiens; and 0.58 in Australopithecus afarensis (AL 288-1). The AP/TR ratio in the midpelvis is 1.61 [+ or -] 0.23 in nonhominid primates (Cebidae, M. mulatta, hylobatids, and pongids), 1.12 [+ or -] 0.11 in humans, and 0.59 in AL 288-1. In monkeys (Cebidae and M. mulatta), hylobatids, pongids, H. sapiens, and AL 288-1, the ratios of the length of the pubic axis over the ischial axis were 0.84 [+ or -] 0.06, 0.95 [+ or -] 0.07, 1.10 [+ or -] 0.15, and 1.46, respectively; the pubis-ilium angles were 96 [+ or -] 11, 120 [+ or -] 10, 131 [+ or -] 11, and 147 degrees, respectively; and the ischium-pubis angles were 106 [+ or -] 11, 86 [+ or -] 8, 96 [+ or -] 7, and 68 degrees, respectively. In none of these pelvic features was AL 288-1 'intermediate' between pongids and H. sapiens. The anatomical peculiarities of the pelvis in AL 288-1 are explained primarily as the result of early adaptation to erect posture, which resulted in the reduction of the distance between the sacroiliac joint and the hip joint. As a consequence, the sacral promontory moved toward the pubic symphysis, and this resulted in shortening of the AP diameter and widening of the TR diameter at the pelvic inlet.

It has previously been reported that brachiating primates, particularly gibbons, are characterized by distinctively straight forelimb long bones, yet no hypotheses have been proposed to explain why straight limb bones may be adaptive to suspensory locomotion. This study explores quantitatively the curvature of the long bones in 13 species of anthropoid primates and analyzes the functional consequences of curvature in biomechanical terms. These analyses demonstrate that, whereas the humeri of gibbons and spider monkeys are functionally less curved than those of other taxa, the ulnae of brachiators are neither more nor less curved than those of other anthropoids, and the gibbon radius is far more curved than would be predicted from body size alone. The humerus is likely significantly less curved in brachiators because of its torsion-dominated loading regime and the greatly increased stress magnitude developed in torsionally loaded curved beams. The large curvature of the radius is localized in the region of attachment of the supinator muscle. Analysis presented here of muscle mass allometry in catarrhines demonstrates that gibbons are characterized by an extremely massive supinator, and the large radial curvature is therefore most likely due to forearm muscle mechanics. This study also demonstrates that the overall pattern of limb bone curvature for anthropoids is distinct from the pattern reported for mammals as a whole. This distinctive scaling relationship may be related to the increased length of the limb bones of primates in comparison to other mammals.

The descriptive and functional morphology of the postcranium of the vertical clinging and leaping prosimians is of great interest in both adaptational and phylogenetic studies of extant and extinct primates. An analysis of patterns of femoral morphology among quadrupedal and saltatory living prosimians indicates the presence of at least two, and possibly three, distinct femoral adaptations to the demands of an arboreal, saltatory existence. Osteological measurements were taken on 277 postcranial skeletons representing eight prosimian families, with skeletal trunk length (Biegert and Maurer, Folia Primatol. 17:142-156, 1972) used as an estimator of body size in both bivariate and multivariate (discriminant function) statistical analyses. Whereas all extant vertical clingers and leapers share certain femoral traits (i.e., long femur, proximally restricted trochanters, verntrally raised patellar articular surface), Galagidae and Tarsiidae share features of the proximal femur (i.e., cylindrical head, large posterior expansion of articular surface onto the neck) that clearly distinguish them from the specialized leapers of the Malagasy Republic (Indriidae and Lepilemur). Thes latter animals closely resemble active quadrupedal Lemuriformes in possessing spherical femoral heads, with little posterior expansion of articular surface and a distinctive greater trochanter shape. Somoe traits suggested as being characteristics of vertical clingers and leapers (i.e., deep femoral condyles facing posteriorly, narrow patellar groove with prominent lateral margin, greater trochanter overhanging anterior aspect of shaft) are shown to be common to all prosimians except the slow-climbing lorisids. The functional significance of aspects of femoral morphology among saltators is discussed, along with the relevance of these results to an assessment of vertical clinging and leaping among extant and extinct primates.

Hip, knee, and ankle joint displacement patterns are compared across both age and speed for five immature vervet monkeys samppled approximately every 6 months over a 3 year period. The analysis indicated that, as a group, the animals displayed no consistent changes in joint patterns as they grow. However, individuals animals showed consistent patterns. There were also no consistent effects of size across animals at the walk-gallop transition. This is contrary to McMahon's prediction (J. Appl. Physiol. 39:619-627, 1975) based upon his elastic-similarity model of animal scaling. With increasing speed, when symmetrical gaits were used, all of the animals tended to show a decrease in the relative positions of the hip, knee, and ankle maximum values. Furthermore, across the walk-gallop transition, the animals tended to show a decrease in the range of ankle and knee movements.

The location of the foramen magnum, with respect to the longitudinal axis of the cranium, and its orientation with respect to the Frankfurt Horizontal, have been studied in a total of 328 modern human and Pan crania. The samples were chosen in order to examine the effect of overall size difference on foramen magnum disposition. Foramen position (expressed as three indices) and inclination are relatively invariant among the modern human samples, but the foramen magnum is consistently, and statistically significantly, more anteriorly located in Pan paniscus than in Pan troglodytes. Sexual dimorphism is virtually non-existent. There is an apparent allometric effect on foramen position, but not on inclination, so that larger crania in the modern human and Pan paniscus samples tend to have more posteriorly situated foramina. The disposition of the foramen is unrelated to cranial base angle of facial prognathism, except that in Pan paniscus its relative anterior location is linked with the more flexed cranial base in that species. These results provide a comparative context for the examination of differences in foramen magnum disposition in fossil hominids. Differences in foramen magnum position and orientation between KNM-ER 1813 and A. africanus are most unlikely to be due to within-taxon variability.

The response variability in primate retinal ganglion cells was examined at photopic levels. The amplitude of the stimulus and the response did not influence the variability, making it additive. Receptive field size and retinal eccentricity did not affect variability. No major differences in variability were observed for all primate ganglion cells. The ganglion cells appear to be the source of noise, because the primate retinal possesses a consistent noise level over the visual field.

The fovea of Old World primates contain three kinds of cones, each suited to a part of the visible spectrum. Research has shown that the short-wave cones are sparse and arranged in a semi-regular pattern. Direct microspectrophotometric measurement of fovea of talapoin monkeys shows that the middle- and long-wave cones have a locally random array and occur in approximately equal proportions. Since it has been postulated that long-wave cones dominate human fovea, these data suggest that further investigation is necessary. If there is such a species difference, an evolutionary explanation should be sought.

Many behavioral and ecological factors influence the degree of expression of canine dimorphism for different reasons. Regardless of its socioecological importance, we know virtually nothing about the processes responsible for the development of canine dimorphism. Our aim here is to describe the developmental process(es) regulating canine dimorphism in extant hominoids, using histological markers of tooth growth. Teeth preserve a permanent record of their ontogeny in the form of short- and long-period incremental markings in both enamel and dentine. We selected 52 histological sections of sexed hominoid canine teeth from a total sample of 115, from which we calculated the time and rate of cuspal enamel formation and the rate at which ameloblasts differentiate along the future enamel-dentine junction (EDJ) to the end of crown formation. Thus, we were able to reconstruct longitudinal growth curves for height attainment in male and female hominoid canines. Male hominoids consistently take longer to form canine crowns than do females (although not significantly so for our sample of Homo). Male orangutans and gorillas occasionally take up to twice as long as females to complete enamel formation. The mean ranges of female canine crown formation times are similar in Pan, Gorilla, and Pongo. Interspecific differences between female Pan canine crown heights and those of Gorilla and Pongo, which are taller, result from differences in rates of growth. Differences in canine crown heights between male Pan and the taller, more dimorphic male Gorilla and Pongo canines result both from differences in total time taken to form enamel and from faster rates of growth in Gorilla and Pongo. Although modern human canines do not emerge as significantly dimorphic in this study, it is well-known that sexual dimorphism in canine crown height exists. Larger samples of sexed modern human canines are therefore needed to identify clearly what underlies this. Am J Phys Anthropol 115:269-283, 2001.

Extant apes are similar to one another, and different from monkeys, in features granting them greater range of forearm rotation and greater size of the muscles that produce this motion. Although these traits may have been independently acquired by the various apes, the possibility arises that such features reflect adaptation to the stem behavior of the hominoid lineage. Anticipating that knowledge of forearm rotatory muscle recruitment during brachiation, vertical climbing, arm-hanging during feeding, and voluntary reaching might point to this stem behavior, we undertook telemetered electromyographic experiments on the supinator, pronator quadratus, ulnar head of pronator teres, and a variety of other upper limb muscles in two gibbons and four chimpanzees. The primary rotator muscles of the hominoid forearm were recruited at high levels in a variety of behaviors. As had been suspected by previous researchers, the supinator is usually active during the support phase of armswinging, but we observed numerous instances of this behavior during which the muscle was inactive. No other muscle took over its role. Kinetic analyses are required to determine how apes can execute body rotation of armswinging without active muscular effort. The one behavior that is common to most extant apes, is rare in monkeys, and which places a consistently great demand on the primary forearm rotatory muscles, is hang-feeding. The muscles of the supporting limb are essential to properly position the body; those of the free limb are essential for grasping food. Since the greater range of forearm rotation characterizing apes is also best explained by adaptation to this behavior, we join previous authors who assert that it lies at the very origin of the Hominoidea. Am J Phys Anthropol 115:253-268, 2001. KEY WORDS muscle; apes; locomotion; suspension; feeding; armswinging; climbing

Constraint has played a major role in brain evolution, but cannot tell the whole story. In primates, adaptive specialization is suggested by the existence of a covarying visual system, and may explain some residual variation in the constraint model. Adaptation may also appear at the microstructural level and in the globally integrated system of brain, body, life history and behavior.

This paper explores the correlates of variation in dental development across the order Primates. We are particularly interested in how 1) dental precocity (percentage of total postcanine primary and secondary teeth that have erupted at selected absolute ages and life cycle stages) and 2) dental endowment at weaning (percentage of adult postcanine occlusal area that is present at weaning) are related to variation in body or brain size and diet in primates. We ask whether folivores have more accelerated dental schedules than do like-sized frugivores, and if so, to what extent this is part and parcel of a general pattern of acceleration of life histories in more folivorous taxa. What is the adaptive significance of variation in dental eruption schedules across the order Primates? We show that folivorous primate species tend to exhibit more rapid dental development (on an absolute scale) than comparably sized frugivores, and their dental development tends to be more advanced at weaning. Our data affirm an important role for brain (rather than body) size as a predictor of both absolute and relative dental development. Tests of alternative dietary hypotheses offer the strongest support for the foraging independence and food processing hypotheses. Am J Phys Anthropol 114:192-214, 2001. [C] 2001 Wiley-Liss, Inc. KEY WORDS dental development; diet; cranial capacity; life histories; primates