Kinematics of the cercopithecine foot on arboreal and terrestrial substrates with implications for the interpretation of hominid terrestrial adaptations

The stereotyped characterizations of quadrupedal foot postures were tested by examining the kinematics of the cercopithecine foot on arboreal and terrestrial supports. Strictly arboreal species were compared with semi-terrestrial species for Cercopithecus, Cercocebus, Lophocebus, and Papio, in semi-natural or experimental settings. Results indicate that the kinematics of the cercopithecine arboreal quadruped differ in degree from stereotypical expectations for an arboreal quadruped. The relatively extended, adducted limb movements of the cercopithecines and the emphasis on the central digit as the functional axis of the foot suggest convergence with terrestrial mammalian cursors, and differ from the platyrrhine or colobine arboreal quadruped. The characteristics of the quadrupedal terrestrial primate foot contrast with the very unique pattern seen in the hominid foot. These contrasts provide a new perspective from which to interpret the hominid adaptation, in which the functional axis has remained fixed between the first and second digits. This pattern differs from virtually all other terrestrial mammals. The influence of bipedalism on this functional pattern is examined.     

A biomechanical analysis of mandibular scaling in old world monkeys

Scaling of mandibular dimensions in male Old World monkeys was investigated. Mandibular condyle length, width, and area were regressed separately against body mass and mandibular length for a total of 14 species of Cercopithecoids. Scaling of mandibular depth and width against both body mass and mandibular length were also investigated. When results of regression analysis using the two different independent variables (body mass and mandibular length) were compared, there were significant pattern differences in scaling of cercopithecines versus colobines. Compared to body mass, male cercopithecines had relatively large mandibles (length, width, and depth) and also relatively large condyles (length, width, and area). However, compared to mandibular length, cercopithecines had relatively transversely thin and shallow mandibles and relatively narrow condyles. It is shown that a “biomechanical” interpretation of mandibular scaling patterns against body mass in Old World monkeys demonstrates only that cercopithecines have prognathic faces, an already well-known and well-documented condition. When the biomechanical effects of prognathic faces are controlled for (by scaling against mandibular length), it is shown that cercopithecines possess special adaptations in condyle length while colobines possess special adaptations in condyle width and mandibular depth and width. These results clearly demonstrate the importance of selecting a relevant reference variable in scaling studies where biomechanical interpretations are attempted.     

A REDRAWN PHYLOGENY OF GUENONS BASED UPON THEIR CALLS—BIOGEOGRAPHICAL IMPLICATIONS

ABSTRACT

A phylogeny of guenons was drawn up from the analysis of the acoustic structure of their cohesion, contact and alarm calls, as well as of the loud calls of the adult males. The plesiomorphic or apomorphic state of every acoustic parameter retained was inferred from comparisons with calls given by papionines and/or colobines. A cladistic method was used for analysing a matrix of species by character.

The proposed phylogeny separates guenons into two groups: the one includes all forest- living arboreal forms, the other most of the terrestrially-adapted species. The latter, together with C. nigroviridis, which lie close to the origin from which all guenons diverged, share a relatively primitive position, while the arboreal species are the most derived living representatives of the taxon. Quite reliable interspecific affinities are found among arboreal forms, while there are some inconsistencies for the more primitive species. Such results suggest that cercopithecines would have undergone a radiation from more or less open habitats into forests, the evolution proceeding from large-bodied, partly-terrestrial forms to smaller arboreal ones.     

THE MODE OF LIFE OF HYPSILOPHODON, THE SUPPOSEDLY ARBOREAL ORNITHOPOD DINOSAUR

Previous discussions of the mode of life of Hypsilophodon (Lower Cretaceous, England) are reviewed, and it is concluded that this primitive ornithopod was cursorial. There are no specific adaptations for an arboreal mode of life, and the hallux was not opposable. Metatarsal I was closely applied along its length to metatarsal II, and the first digit moved parallel to or. slightly away from the other digits. Relative to the trunk, the hind limb is long, with an elongate tibia and metatarsus, so that the proportions of the different regions fall in the range for cursorial mammals.     

Molecular phylogeny of Old World monkeys (Cercopithecidae) as inferred from gamma-globin DNA sequences

DNA sequence data of the nuclear-encoded gamma1-gamma2-globin duplication region were used to examine the phylogenetic relationships of 16 cercopithecid (Old World monkey) species representing 12 extant genera. Morphology- and molecular-based hypotheses of Old World monkey branching patterns are generally congruent, except for generic relationships within the subtribe Papionina. The cercopithecids divide into colobines (leaf-eating monkeys) and cercopithecines (cheek-pouched monkeys). The colobines examined by the DNA data divide into an Asian clade (Nasalis, proboscis monkeys; Trachypithecus, langurs) and an African clade (Colobus, colobus monkeys). The cercopithecines divide into tribes Cercopithecini (Erythrocebus, patas monkey; Chlorocebus, green monkeys; Cercopithecus, guenons) and Papionini. Papionins divide into subtribes Macacina (Macaca, macaques) and Papionina (Papio, hamadryas baboons; Mandrillus, drills and mandrills; Theropithecus, gelada baboons; Lophocebus, arboreal mangabeys; Cercocebus, terrestrial mangabeys). In a morphologically based classification, Mandrillus is a subgenus of Papio, whereas Lophocebus is a subgenus of Cercocebus. In contrast, the molecular evidence treats Mandrillus as a subgenus of Cercocebus, and treats both Theropithecus and Lophocebus as subgenera of Papio. Local molecular clock divergence time estimates were used as a yardstick in a "rank equals age" system to propose a reduction in taxonomic rank for most clades within Cercopithecidae.     

Dental morphometric variation between African and Asian colobines, with special reference to the other Old World monkeys

In order to reveal differences between Asian and African colobines (nonhuman primates) in terms of dietary adaptation and evolutionary development, a large number of the species of the cercopithecoids (Old World monkeys) was analyzed with morphometric methods. In addition to the raw data and ratios, deviations of the colobines, predicted from allometric baselines derived from the cercopithecines, were analyzed by univariate and multivariate analyses. Some results indicated that there exists significant differentiation between colobines and cercopithecines; the latter exhibit a larger dental scale relative to body size, and the less developed front teeth of the colobines may be related to their fewer frequent incisal use, compared with those of the cercopithecines. With regard to variations between the two subtribes of the colobines, which are found in African (Colobina) and Asia (Presbytina), the Asian subtribe displays a larger scale of postcanine teeth, referring to the results of the raw data. This may correspond to their larger body size. While ratios were considered, the variation between Presbytina and Colobina was diminished greatly. This implies that, unlike the scenario postulated to reflect the relationships between colobines and cercopithecines--which supposes that their differentiation is in both size and shape--the variation between the two subtribes is principally size associated: relative to body size Colobina exhibits more emphasized incisors, but less developed postcanine teeth--with the exception of width of M3s. In other words, the relationships between teeth and body size of the African colobines are more similar to those of the cercopithecines. This implies, compared to their Asian partners, that African colobines share more similarities with cercopithecines. This may be related to the episodes in which African species underwent a longer period of sharing environmental and climatic patterns with the cercopithecines that moved to Asia about 5 or 8 million years ago. Canines were found to be important in distinguishing colobines from cercopithecines and in separating one subtribe from the other.     

Jaw morphology and function in living and fossil old world monkeys

This allometric investigation on a sample of 29 cercopithecine and 22 colobine taxa augments the data and implications of prior work on subfamilial variation in mandibular form and function in recent Cercopithecidae. To increase the size range encompassed by living cercopithecines and colobines, I included many of the larger-bodied fossil specimens. These analyses serve to fill a gap in our understanding of size-related changes in masticatory function and symphyseal morphology and curvature in extant and extinct Old World monkeys. Results of subfamilial scaling comparisons indicate that for a given jaw length, colobines possess significantly more robust corpora and symphyses than those of cercopithecines, especially at smaller sizes. Following from previous work, the most plausible explanation for why the subfamilies differ in relative corporeal and symphyseal dimensions is that colobine mandibles experience elevated loads and greater repetitive loading during mastication due, on average, to processing a diet of tough leaves and/or seeds. Although colobines have relatively larger symphyses, subfamilial analyses of symphyseal curvature demonstrate that they evince less symphyseal curvature vis-à-vis cercopithecines of a common size. Moreover, both subfamilies exhibit similar allometric changes in the degree of curvature, such that larger-bodied Old World monkeys have more curved symphyses than those of smaller taxa. Subfamilial scaling analyses also indicate that colobines possess a shorter M2 bite-point length relative to masseter lever-arm length, but not versus temporalis lever-arm length. Thus, as compared to cercopithecines, colobines can recruit less masseter-muscle force to produce similar bite forces during mastication. In both clades, M² bite-point length scales with positive allometry relative to masseter lever-arm length, such that larger species are less efficient at generating molar bite forces. This seems especially important due to the lack of subfamily difference in M² bite-point:temporalis lever-arm scaling (which is isometric across cercopithecids). A consideration of extinct cercopithecids indicates that many of the large-bodied papionins have more robust corpora, due perhaps to a diet which was of similar toughness to that of extant and extinct colobines. However, the biomechanical arrangements of the masseter and temporalis in all but one fossil cercopithecine and all of the fossil colobine specimens are much as predicted for a subfamilial member of its skull size. That most large-bodied papionins with tougher diets nonetheless maintain a less efficient jaw-muscle configuration may be due to stronger offsetting selection for increased relative canine size and gape.     

Folivory, frugivory, and postcanine size in the cercopithecoidea revisited

At a given body mass, folivorous colobines have smaller postcanine teeth than frugivorous cercopithecines. This distinction is a notable exception to the general tendency for folivorous primates to have relatively larger postcanine tooth rows than closely related frugivores. The reason for this anomalous pattern is unclear, but one potential explanation is that the difference in facial size between these two subfamilies confounds the comparison-i.e., it may be that the large postcanine teeth of cercopithecines are a consequence of their large faces. The goal of this study was to test this hypothesis. Phylogenetic comparative methods were used to examine the relationships among postcanine area, facial size, and body mass in 29 anthropoid primates, including eight colobines and eight cercopithecines. Results indicate that there is a strong and highly significant partial correlation between postcanine area and facial size when body mass is held constant, which supports the hypothesis that facial size has an important influence on postcanine size. Moreover, colobines have larger postcanine teeth relative to facial size than cercopithecines. Surprisingly, when facial size is held constant, the partial correlation between postcanine area and body mass is weak and nonsignificant. These results suggest that facial size may be more appropriate than body mass for size-adjusting postcanine measurements in some contexts. A phylogenetic comparative test of the association between diet and relative postcanine size (scaled using facial size) confirms that folivorous anthropoids are characterized by relatively large postcanine teeth in comparison to closely related nonfolivores.     

Mouse hallucal metatarsal cross‐sectional geometry in a simulated fine branch niche

Mice raised in experimental habitats containing an artificial network of narrow “arboreal” supports frequently use hallucal grasps during locomotion. Therefore, mice in these experiments can be used to model a rudimentary form of arboreal locomotion in an animal without other morphological specializations for using a fine branch niche. This model would prove useful to better understand the origins of arboreal behaviors in mammals like primates. In this study, we examined if locomotion on these substrates influences the mid‐diaphyseal cross‐sectional geometry of mouse metatarsals. Thirty CD‐1/ICR mice were raised in either arboreal (composed of elevated narrow branches of varying orientation) or terrestrial (flat ramps and walkways that are stratified) habitats from weaning (21 days) to adulthood (≥4 months). After experiments, the hallucal metatarsal (Mt1) and third metatarsal (Mt3) for each individual were isolated and micro‐computed tomography (micro‐CT) scans were obtained to calculate mid‐shaft cross‐sectional area and polar section modulus. Arboreal mice had Mt1s that were significantly more robust. Mt3 cross sections were not significantly different between groups. The arboreal group also exhibited a significantly greater Mt1/Mt3 ratio for both robusticity measures. We conclude that the hallucal metatarsal exhibits significant phenotypic plasticity in response to arboreal treatment due to habitual locomotion that uses a rudimentary hallucal grasp. Our results support the hypothesis that early adaptive stages of fine branch arboreality should be accompanied by a slightly more robust hallux associated with the biomechanical demands of this niche. J. Morphol. 276:759–765, 2015. © 2015 Wiley Periodicals, Inc.     

The Hand of Cercopithecoides williamsi (Mammalia,Primates): Earliest Evidence for Thumb Reduction among Colobine Monkeys

Thumb reduction is among the most important features distinguishing the African and Asian colobines from each other and from other Old World monkeys. In this study we demonstrate that the partial skeleton KNM-ER 4420 from Koobi Fora, Kenya, dated to 1.9 Ma and assigned to the Plio-Pleistocene colobine species Cercopithecoides williamsi, shows marked reduction of its first metacarpal relative to the medial metacarpals. Thus, KNM-ER 4420 is the first documented occurrence of cercopithecid pollical reduction in the fossil record. In the size of its first metacarpal relative to the medial metacarpals, C. williamsi is similar to extant African colobines, but different from cercopithecines, extant Asian colobines and the Late Miocene colobines Microcolobus and Mesopithecus. This feature clearly links the genus Cercopithecoides with the extant African colobine clade and makes it the first definitive African colobine in the fossil record. The postcranial adaptations to terrestriality in Cercopithecoides are most likely secondary, while ancestral colobinans (and colobines) were arboreal. Finally, the absence of any evidence for pollical reduction in Mesopithecus implies either independent thumb reduction in African and Asian colobines or multiple colobine dispersal events out of Africa. Based on the available evidence, we consider the first scenario more likely.     

The morphological basis of hallucal orientation in extant birds

The perching foot of living birds is commonly characterized by a reversed or opposable digit I (hallux). Primitively, the hallux of nonavian theropod dinosaurs was unreversed and lay parallel to digits II-IV. Among basal birds, a unique digital innovation evolved in which the hallux opposes digits II-IV. This digital configuration is critical for grasping and perching. I studied skeletons of modern birds with a range of hallucal designs, from unreversed (anteromedially directed) to fully reversed (posteriorly directed). Two primary correlates of hallucal orientation were revealed. First, the fossa into which metatarsal I articulates is oriented slightly more posteriorly on the tarsometatarsus, rotating the digit as a unit. Second, metatarsal I exhibits a distinctive torsion of its distal shaft relative to its proximal articulation with the tarsometatarsus, reorienting the distal condyles and phalanges of digit I. Herein, I present a method that facilitates the re-evaluation of hallucal orientation in fossil avians based on morphology alone. This method also avoids potential misinterpretations of hallucal orientation in fossil birds that could result from preserved appearance alone.     

尾羽龙(Caudipteryx)的新材料及其重要骨骼特征的补充和修订

尾羽龙和原始祖鸟一起被认为是最早发现的带有真正鸟类羽毛的恐龙（Ji et al., 1998）,迄今已发现的尾羽龙包括邹氏尾羽龙（Caudipteryx zoui）和董氏尾羽龙（Caudipteryx dongi）两种（周忠和、汪筱林,2000）,前者包括保存在中国地质博物馆的NGMC 97*4朅和NGMC 97*9朅两件标本,而后者依据的材料仅为保存在中国科学院古脊椎动物与古人类研究所的V 12344。以上标本都不是十分完整。本文依据最近新发现的两件几乎完整的尾羽龙标本,对该属的一些重要形态特征进行补充和修订,以期对其系统关系的讨论及其他相关理论问题的研究提供新的…     

Comparative functional morphology of the primate peroneal process

The first metatarsal of living Primates is characterized by a well-developed peroneal process, which appears proportionally larger in prosimians than in anthropoids. A large peroneal process has been hypothesized to: 1) reflect powerful hallucal grasping, 2) act as a buttress to reduce strain from loads acting on the entocuneiform-first metatarsal joint during landing and grasping after a leap, and/or 3) correlate with differences in physiological abduction of the hallux. In this study, we address the latter two hypotheses by comparing the morphology of the peroneal process in 143 specimens representing 37 species of extant prosimians, platyrrhine anthropoids, and tupaiids (tree shrews) that engage in different locomotor behaviors. In particular, we compare taxa that vary in leaping frequency and hallucal abduction. Linear and angular measurements on the first metatarsal were obtained to evaluate differences in relative peroneal process thickness and length, first metatarsal abduction angle, and overall first metatarsal shape. Leaping frequency was significantly correlated only with relative peroneal process thickness within extant lorisoids. Relative process length was positively correlated with the angle of hallucal abduction within prosimians; this angle is significantly greater in prosimians than anthropoids. Multivariate analyses of metatarsal shape effectively separate species along phylogenetic lines, but not by locomotor behaviors. The hypothesis that the peroneal process on the first metatarsal reduces the loads on the entocuneiform-first metatarsal joint during landing after a leap is in part supported by data from extant lorisoids (i.e., slow quadrupedal lorises vs. leaping galagos). A peroneal process of greater length within prosimians may serve to increase the lever arm for the peroneus longus muscle in order to prevent hyper-abduction, followed by inversion in locomotor situations where the animal's weight is born on a highly divergent/abducted hallux.     

Intrinsic hand proportions of euarchontans and other mammals: implications for the locomotor behavior of plesiadapiforms

Arboreal primates have distinctive intrinsic hand proportions compared with many other mammals. Within Euarchonta, platyrrhines and strepsirrhines have longer manual proximal phalanges relative to metacarpal length than colugos and terrestrial tree shrews. This trait is part of a complex of features allowing primates to grasp small-diameter arboreal substrates. In addition to many living and Eocene primates, relative elongation of proximal manual phalanges is also present in most plesiadapiforms. In order to evaluate the functional and evolutionary implications of manual similarities between crown primates and plesiadapiforms, we measured the lengths of the metacarpal, proximal phalanx, and intermediate phalanx of manual ray III for 132 extant mammal species (n=702 individuals). These data were compared with measurements of hands in six plesiadapiform species using ternary diagrams and phalangeal indices. Our analyses reveal that many arboreal mammals (including some tree shrews, rodents, marsupials, and carnivorans) have manual ray III proportions similar to those of various arboreal primates. By contrast, terrestrial tree shrews have hand proportions most similar to those of other terrestrial mammals, and colugos are highly derived in having relatively long intermediate phalanges. Phalangeal indices of arboreal species are significantly greater than those of the terrestrial species in our sample, reflecting the utility of having relatively long digits in an arboreal context. Although mammals known to be capable of prehensile grips demonstrate long digits relative to palm length, this feature is not uniquely associated with manual prehension and should be interpreted with caution in fossil taxa. Among plesiadapiforms, Carpolestes, Nannodectes, Ignacius, and Dryomomys have manual ray III proportions that are unlike those of most terrestrial species and most similar to those of various arboreal species of primates, tree shrews, and rodents. Within Euarchonta, Ignacius and Carpolestes have intrinsic hand proportions most comparable to those of living arboreal primates, while Nannodectes is very similar to the arboreal tree shrew Tupaia minor. These results provide additional evidence that plesiadapiforms were arboreal and support the hypothesis that Euarchonta originated in an arboreal milieu.     

The socioecology of infant handling in primates: Is the current model convincing?

A strong interest shown by females towards infants other than their own is one of the most consistent behavioral traits found in primates, including humans. Species differences exist, however, in the extent mothers allow other group members to interact with their offspring. Socioecological theory predicts that in species characterized by relaxed, egalitarian dominance relations mothers should allow extensive interactions between their infants and other individuals from the first weeks of life, while in species characterized by nepotistic and despotic dominance relations maternal tolerance of infant handling should be low. While this model received some support from a comparison between colobines and some cercopithecines, several other species, including the Barbary macaque, do not appear to fit easily into the framework. In fact, only about half of all well-studied species follow the predicted pattern, suggesting that other factors, associated with the costs and benefits of the behavior, must be invoked to explain the variation in mothering styles and infant handling found in primates.     

A resampling approach and implications for estimating the phalangeal index from unassociated hand bones in fossil primates

Primate fossil assemblages often have metacarpals and phalanges from which functional/behavioral interpretations may be inferred. For example, intrinsic hand proportions can indicate hand function and substrate use. But, estimates of intrinsic hand proportions from unassociated hand elements can be imperfect due to digit misattribution. Although isolated metacarpals can be identified to a specific digit, phalanges are difficult to assign to a specific ray. We used a resampling approach to evaluate how estimates of intrinsic hand proportions are affected by such uncertainty. First, the phalangeal index—intermediate phalanx length plus proximal phalanx length divided by metacarpal length—for the third digit was calculated for associated specimens of terrestrial, semiterrestrial, and arboreal taxa. We then used resampling procedures to generate distributions of “composite digits” based on resampled ratios in which phalanges from the second, fourth, and fifth rays, and from different individuals, were chosen randomly. Results confirm that the phalangeal index for associated third digits significantly discriminates groups. We also found that resampled ratios had significantly lower means, indicating that using composite digits is prone to systematic underestimation. Resampled ratios also generated distributions with greater variance around the means that obscured distinctions between groups, although significant differences between the most arboreal and terrestrial taxa are maintained. We conclude that using unassociated phalanges to calculate a phalangeal index is prone to sampling bias. Nevertheless, a resampling approach has the potential to inform estimates of hand proportions for fossil taxa, provided that the comparative sample is constrained to mimic the fossil composition. Am J Phys Anthropol 151:280–289, 2013. © 2013 Wiley Periodicals, Inc.     

Functional morphology of the hindlimb of tupaiids (Mammalia,Scandentia) and its phylogenetic implications

In this study, the hindlimb of 12 species of tupaiids was analyzed functionally and compared to that of primates, dermopterans, and chiropterans. Many aspects of the tupaiid hindlimb vary in relation to differential substrate use. These differences include width of the ilium, shape of the acetabulum, size of the anterior inferior iliac spine, size of the greater and third trochanters, depth of the femoral condyles, shape of the patellar groove, and size of the tibial tuberosity. The hindlimb of the arboreal Ptilocercus lowii, the only ptilocercine, is better adapted for arboreal locomotion, whereas that of tupaiines is better adapted for rapid terrestrial (or scansorial) locomotion. The hindlimb of Ptilocercus seems to be habitually flexed and has more joint mobility, a condition necessary for movement on uneven, discontinuous arboreal supports. The tarsus of Ptilocercus facilitates inversion of the foot and its grasping hallux is capable of a great range of abduction. Tupaiines, on the other hand, are characterized by more extended hindlimbs and less mobility in their joints. These restricted joints limit movements more to the parasagittal plane, which increases the efficiency of locomotion on a more even and continuous surface like the ground. The hindlimb of tupaiines is adapted for powerful flexion and extension. Even the most arboreal tupaiines remain similar to terrestrial tupaiines in their hindlimb morphology, which probably reflects the terrestrial ancestry of Tupaiinae (but not Tupaiidae). Many attributes of the tupaiid hindlimb, especially those of the foot, reflect the arboreal ancestry of Tupaiidae and it is proposed that the ancestral tupaiid was arboreal like Ptilocercus. Also, compared to the hindlimb character states of tupaiines, those of Ptilocercus are more similar to those of other archontans, and it is proposed that the hindlimb features of Ptilocercus are primitive for the Tupaiidae. Hence, Ptilocercus should be considered in any phylogenetic analysis that includes Scandentia.     

Telemetered electromyography of peroneus longus in Varecia variegata and Eulemur rubriventer: implications for the functional significance of a large peroneal process

A foot specialized for grasping small branches with a divergent opposable hallux (hallucal grasping) represents a key adaptive complex characterizing almost all arboreal non-human euprimates. Evolution of such grasping extremities probably allowed members of a lineage leading to the common ancestor of modern primates to access resources available in a small-branch niche, including angiosperm products and insects. A better understanding of the mechanisms by which euprimates use their feet to grasp will help clarify the functional significance of morphological differences between the euprimate grasp complex and features representing specialized grasping in other distantly related groups (e.g., marsupials and carnivorans) and in closely related fossil taxa (e.g., plesiadapiforms). In particular, among specialized graspers euprimates are uniquely characterized by a large peroneal process on the base of the first metatarsal, but the functional significance of this trait is poorly understood. We tested the hypothesis that the large size of the peroneal process corresponds to the pull of the attaching peroneus longus muscle recruited to adduct the hallux during grasping. Using telemetered electromyography on three individuals of Varecia variegata and two of Eulemur rubriventer, we found that peroneus longus does not generally exhibit activity consistent with an important function in hallucal grasping. Instead, extrinsic digital flexor muscles and, sometimes, the intrinsic adductor hallucis are active in ways that indicate a function in grasping with the hallux. Peroneus longus helps evert the foot and resists its inversion. We conclude that the large peroneal tuberosity that characterizes the hallucal metatarsal of prosimian euprimates does not correlate to "powerful" grasping with a divergent hallux in general, and cannot specifically be strongly linked to vertical clinging and climbing on small-diameter supports. Thus, the functional significance of this hallmark, euprimate feature remains to be determined.     

Size and shape of the mandibular condyle in primates

The relationships between the size of the articular surface of the mandibular condyle and masticatory muscle size, tooth size, diet, and biomechanical variables associated with mastication were studied by taking 12 measurements on skulls of 253 adult female anthropoid primates, including three to ten specimens from each of 32 species. In regressions of condylar length, width, or area against body weight, logarithmic transformations substantially improve the fit of the equations compared with untransformed data. There is a strong relationship between condylar measurements and body weight, with all correlations being .94 or higher. The slopes of the allometric regressions of length, width, and area of the condylar head indicate slight positive allometry with body size. Folivorous primates have smaller condyles than frugivorous primates, and colobines have smaller condyles than cebids, cercopithecines, or hominoids. When colobines are eliminated, the differences between frugivores and folivores are not significant. However, the two species with the relatively largest condyles are Pongo pygmaeus and Cercocebus torquatus, suggesting that there may be a relationship between unusually large condylar dimensions and the ability to crack hard nuts between the teeth. Cranial features having strong positive correlations with condylar dimensions include facial prognathism, maxillary incisor size, maxillary postcanine area, mandibular ramus breadth, and temporal fossa area. These data are interpreted as indicating that relatively large condyles are associated with relatively large masticatory muscles, relatively inefficient mandibular biomechanics, and a large dentition. These relationships support the growing evidence that the temporomandibular joint is a stress-bearing joint in normal function.