Locomotor behavior of wild orangutans (Pongo pygmaeus wurmbii) in disturbed peat swamp forest, Sabangau, Central Kalimantan, Indonesia

This study examined the locomotor behavior of wild Bornean orangutans (P. p. wurmbii) in an area of disturbed peat swamp forest (Sabangau Catchment, Indonesia) in relation to the height in the canopy, age-sex class, behavior (feeding or traveling), and the number of supports used to bear body mass. Backward elimination log-linear modeling was employed to expose the main influences on orangutan locomotion. Our results showed that the most important distinctions with regard to locomotion were between suspensory and compressive, or, orthograde (vertical trunk) and pronograde (horizontal trunk) behavior. Whether orangutans were traveling or feeding had the most important influence on locomotion whereby compressive locomotion had a strong association with feeding, suspensory locomotion had a strong association with travel in the peripheral strata using multiple supports, whereas vertical climb/descent and oscillation showed a strong association with travel on single supports in the core stratum. In contrast to theoretical predictions on positional behavior and body size, age-sex category had a limited influence on locomotion. The study revealed that torso orthograde suspension dominates orangutan locomotion, concurring with previous studies in dipterocarp forest. But, orangutans in the Sabangau exhibited substantially higher frequencies of oscillatory locomotion than observed at other sites, suggesting this behavior confers particular benefits for traversing the highly compliant arboreal environment typical of disturbed peat swamp forest. In addition, torso pronograde suspensory locomotion was observed at much lower levels than in the Sumatran species. Together these results highlight the necessity for further examination of differences between species, which control for habitat.     

Comparative and functional anatomy of phalanges in<Emphasis Type="Italic"> Nacholapithecus kerioi</Emphasis>, a Middle Miocene hominoid from northern Kenya

We describe phalanges of the KNM-BG 35250 Nacholapithecus kerioi skeleton from the Middle Miocene of Kenya. Phalanges of N. kerioi display similarities to those of Proconsul heseloni despite their enhanced robusticity. They do not show highly specialized features as in living suspensory primates. However, N. kerioi manifests several distinctive features that are observed in neither living arboreal quadrupeds nor P. heseloni or P. nyanzae. The most remarkable of them is its phalangeal elongation. N. kerioi phalanges (particularly pedal) are as long as those of Pan despite its much smaller body size. While lengthened digits enable a secure grip of supports and are especially adaptive for grasping large vertical trunks, the skeletal and soft tissues are subjected to greater stress. Probably, strong selective pressures favored powerful hallucal/pollical assisted grips. Although this functional adaptation does not exclude the possible use of the terrestrial environment, arboreal behavioral modes must have been crucial in its positional repertoire. N. kerioi is distinguished from P. heseloni in the greater size of its manual phalanges over its pedal phalanges. These derived features of N. kerioi suggest positional modes supporting more weight on the forelimb, and which occur more frequently on vertical supports. If Proconsul is referred to as an "above-branch arboreal quadruped" with a deliberate and effective climbing capability, N. kerioi may be thought of as an "orthograde climber". While living apes are powerful orthograde climbers, they are also more or less suspensory specialists. Suspensory behavior (plus climbing) and pronograde quadrupedalism (plus climbing) are the two main arboreal behavioral adaptations in living anthropoids. Thus, N. kerioi is an unusual fossil primate in that it cannot be incorporated into this dichotomy. It is plausible that a N. kerioi-like orthograde climber with large forelimbs and cheiridia was a precursor of suspensory living apes, and N. kerioi may demonstrate what an initial hominoid of this grade might have looked like.     

Climbing,brachiation, and terrestrial quadrupedalism: Historical precursors of hominid bipedalism

The vertical-climbing account of the evolution of locomotor behavior and morphology in hominid ancestry is reexamined in light of recent behavioral, anatomical, and paleontological findings and a more firmly established phylogeny for the living apes. The behavioral record shows that African apes, when arboreal, are good vertical climbers, and that locomotion during traveling best separates the living apes into brachiators (gibbons), scrambling/climbing/brachiators (orangutans), and terrestrial quadrupeds (gorillas and chimpanzees). The paleontological record documents frequent climbing as an ancestral catarrhine ability, while a reassessment of the morphology of the torso and forelimb in living apes and Atelini suggests that their shared unique morphological pattern is best explained by brachiation and forelimb suspensory positional behavior. Further, evidence from the hand and foot points to a terrestrial quadrupedal phase in hominoid evolution prior to the adoption of bipedalism. The evolution of positional behavior from early hominoids to hominids appears to have begun with an arboreal quadrupedal-climbing phase and proceeded though an orthograde, brachiating, forelimb-suspensory phase, which was in turn followed by arboreal and terrestrial quadrupedal phases prior to the advent of hominid bipedality. The thesis that protohominids climbed down from the trees to become terrestrial bipeds needs to be reexamined in light of a potentially long history of terrestriality in the ancestral protohominid. © 1996 Wiley-Liss, Inc.     

Positional behavior of long-tailed macaques (Macaca fascicularis) in northern Sumatra

Although the majority of extant primates are described as "quadrupedal," there is little information available from natural habitats on the locomotor and postural behavior of arboreal primate quadrupeds that are not specialized for leaping. To clarify varieties of quadrupedal movement, a quantitative field study of the positional behavior of a highly arboreal cercopithecine, Macaca fascicularis, was conducted in northern Sumatra. At least 70% of locomotion in travel, foraging, and feeding was movement along continuous substrates by quadrupedalism and vertical climbing. Another 14-25% of locomotion was across substrates by pronograde clambering and vertical clambering. The highest frequency of clambering occurred in foraging for insects, and on the average smaller substrates were used in clambering than during quadrupedal movement. All postural behavior during foraging and feeding was above-substrate, largely sitting. Locomotion across substrates requires grasping branches of diverse orientations, sometimes displaced away from the animal's body. The relatively low frequency of across-substrate locomotion appears consistent with published analyses of cercopithecoid postcranial morphology, indicating specialization for stability of limb joints and use of limbs in parasagittal movements, but confirmation of this association awaits interspecific comparisons that make the distinction between along- and across-substrate forms of locomotion. It is suggested that pronograde clambering as defined in this study was likely a positional mode of considerable importance in the repertoire of Proconsul africanus and is a plausible early stage in the evolution of later hominoid morphology and locomotor behavior.     

Positional behavior in the Hominoidea

Quantitative studies on the positional behavior of members of the Hominoidea are compared in order (1) to identify consistencies across the superfamily, (2) to contrast ape positional behavior with that of Old World monkeys (forest-livingPapio anubis were chosen for study to reduce body size effects), and (3) to identify distinctive behaviors in each of the ape taxa. Differences in the way behaviors were sampled in the various studies necessitated considering posture and locomotion separately. Unimanual arm-hanging and vertical climbing were the most distinctive shared postural and locomotor modes among the apes (the gorilla excepted), constituting ≥5.0% and ≥4.9% of all behavior in each species. Arm-hanging and brachiation (sensu stricto) frequencies were the highest by far in hylobatids. Hand-foot hanging, bipedal posture, and clambering, an orthograde suspensory locomotion assisted by the hindlimbs, were more common in orangutans than in any other hominoid. Sitting and walking were observed in the highest frequencies in the African apes but were no more common than in the baboon. Relatively high frequencies of brachiation (sensu stricto) were reported for all apes except chimpanzees and gorillas. Brachiation and arm-hanging were kinematically different in apes and baboons, involving complete humeral abduction only in the former, whereas vertical climbing appeared to be kinematically similar in apes and baboons. It is concluded that the morphological specializations of the apes may be adaptations to (1) the unique physical demands of arm-hanging and (2) less kinematically distinct, but still quantitatively significant, frequencies of vertical climbing.     

Pierolapithecus and the functional morphology of Miocene ape hand phalanges: paleobiological and evolutionary implications

The partial skeleton of Pierolapithecus, which provides the oldest unequivocal evidence of orthogrady, together with the recently described phalanges from Pa?alar most likely attributable to Griphopithecus, provide a unique opportunity for understanding the changes in hand anatomy during the pronogrady/orthogrady transition in hominoid evolution. In this paper, we describe the Pierolapithecus hand phalanges and compare their morphology and proportions with those of other Miocene apes in order to make paleobiological inferences about locomotor evolution. In particular, we investigate the orthograde/pronograde evolutionary transition in order to test whether the acquisition of vertical climbing and suspension were decoupled during evolution. Our results indicate that the manual phalanges of Miocene apes are much more similar to one another than to living apes. In particular, Miocene apes retain primitive features related to powerful-grasping palmigrady on the basal portion, the shaft, and the trochlea of the proximal phalanges. These features suggest that above-branch quadrupedalism, inherited from stem hominoids, constituted a significant component of the locomotor repertories of different hominoid lineages at least until the late Miocene. Nonetheless, despite their striking morphological similarities, several Miocene apes do significantly differ in phalangeal curvature and/or elongation. Hispanopithecus most clearly departs by displaying markedly-curved and elongated phalanges, similar to those in the most suspensory of the extant apes (hylobatids and orangutans). This feature agrees with several others that indicate orang-like suspensory capabilities. The remaining Miocene apes, on the contrary, display low to moderate phalangeal curvature, and short to moderately-elongated phalanges, which are indicative of the lack of suspensory adaptations. As such, the transition from a pronograde towards an orthograde body plan, as far as this particular anatomical region is concerned, is reflected only in somewhat more elongated phalanges, which may be functionally related to enhanced vertical-climbing capabilities. Our results therefore agree with the view that hominoid locomotor evolution largely took place in a mosaic fashion: just as taillessness antedated the acquisition of an orthograde body plan, the emergence of the latter—being apparently related only to vertical climbing—also preceded the acquisition of suspensory adaptations, as well as the loss of primitively-retained, palmigrady-related features.     

Locomotor ecology of wild orangutans (Pongo pygmaeus abelii) in the Gunung Leuser Ecosystem, Sumatra, Indonesia: a multivariate analysis using log-linear modelling

The large body mass and exclusively arboreal lifestyle of Sumatran orangutans identify them as a key species in understanding the dynamic between primates and their environment. Increased knowledge of primate locomotor ecology, coupled with recent developments in the standardization of positional mode classifications (Hunt et al. [1996] Primates 37:363-387), opened the way for sophisticated multivariate statistical approaches, clarifying complex associations between multiple influences on locomotion. In this study we present a log-linear modelling approach used to identify key associations between orangutan locomotion, canopy level, support use, and contextual behavior. Log-linear modelling is particularly appropriate because it is designed for categorical data, provides a systematic method for testing alternative hypotheses regarding interactions between variables, and allows interactions to be ranked numerically in terms of relative importance. Support diameter and type were found to have the strongest associations with locomotor repertoire, suggesting that orangutans have evolved distinct locomotor modes to solve a variety of complex habitat problems. However, height in the canopy and contextual behavior do not directly influence locomotion: instead, their effect is modified by support type and support diameter, respectively. Contrary to classic predictions, age-sex category has only limited influence on orangutan support use and locomotion, perhaps reflecting the presence of arboreal pathways which individuals of all age-sex categories follow. Effects are primarily related to a tendency for adult, parous females to adopt a more cautious approach to locomotion than adult males and immature subjects.     

Investigating the form-function interface in African apes: Relationships between principal moments of area and positional behaviors in femoral and humeral diaphyses

Investigations of cross-sectional geometry in nonhuman primate limb bones typically attribute shape ratios to qualitative behavioral characterizations, e.g., leaper, slow climber, brachiator, or terrestrial vs. arboreal quadruped. Quantitative positional behavioral data, however, have yet to be used in a rigorous evaluation of such shape-behavior connections. African apes represent an ideal population for such an investigation because their relatedness minimizes phylogenetic inertia, they exhibit diverse behavioral repertoires, and their locomotor behaviors are known from multiple studies. Cross-sectional data from femoral and humeral diaphyses were collected for 222 wild-shot specimens, encompassing Pan paniscus and all commonly recognized African ape subspecies. Digital representations of diaphyseal cross sections were acquired via computed tomography at three locations per diaphysis. Locomotor behaviors were pooled broadly into arboreal and terrestrial categories, then partitioned into quadrupedal walking, quadrumanous climbing, scrambling, and suspensory categories. Sex-specific taxonomic differences in ratios of principal moments of area (PMA) were statistically significant more often in the femoral diaphysis than the humeral diaphysis. While it appears difficult to relate a measure of shape (e.g., PMA ratio) to individual locomotor modes, general locomotor differences (e.g., percentage arboreal vs. terrestrial locomotion) are discerned more easily. As percentage of arboreal locomotion for a group increases, average cross sections appear more circular. Associations between PMA ratio and specific locomotor behaviors are less straightforward. Individual behaviors that integrate eccentric limb positions (e.g., arboreal scrambling) may not engender more circular cross sections than behaviors that incorporate repetitive sagittal movements (e.g., quadrupedal walking) in a straightforward manner.     

Positional behavior of Siberian chipmunks (Tamias sibiricus) in captivity

Arboreal and semi-arboreal mammals have remarkably diverse positional behavior and associated morpho-functional adaptations related to the three-dimensional nature of their arboreal habitat. In this context, we investigated the positional behavior of captive Siberian chipmunks (Tamias sibiricus), small bodied semi-arboreal sciurids, in an aviary-type wire-mesh cage containing both terrestrial and arboreal supports. We sampled four adult individuals during a five-month period using focal animal sampling every 30 s. Results showed that animals preferred 8–10 cm horizontal supports and always avoided vertical supports. Locomotion occurred on both terrestrial and 8–10 cm arboreal supports whereas postural behavior occurred primarily on 8–10 cm arboreal supports. Quadrupedal walk dominated during locomotion, and occurred primarily on terrestrial horizontal supports, as is observed for other squirrels. The predominance of quadrupedal locomotion is consistent with the postcranial morphology of chipmunks. In contrast, clawed locomotion occurred on wire mesh and on >13 cm arboreal vertical supports. Finally, pronograde and orthograde sitting, both on 8–10 cm arboreal supports and on terrestrial supports, were the predominant postures, implying general predisposition to selection of stable postures on stable supports for food item manipulation and ingestion.     

Functional aspects of strepsirrhine lumbar vertebral bodies and spinous processes

The relationship between form and function in the lumbar vertebral column has been well documented among platyrrhines and especially catarrhines, while functional studies of postcranial morphology among strepsirrhines have concentrated predominantly on the limbs. This morphometric study investigates biomechanically relevant attributes of the lumbar vertebral morphology of 20 species of extant strepsirrhines. With this extensive sample, our goal is to address the influence of positional behavior on lumbar vertebral form while also assessing the effects of body size and phylogenetic history. The results reveal distinctions in lumbar vertebral morphology among strepsirrhines in functional association with their habitual postures and primary locomotor behaviors. In general, strepsirrhines that emphasize pronograde posture and quadrupedal locomotion combined with leaping (from a pronograde position) have the relatively longest lumbar regions and lumbar vertebral bodies, features promoting sagittal spinal flexibility. Indrids and galagonids that rely primarily on vertical clinging and leaping with orthograde posture share a relatively short (i.e., stable and resistant to bending) lumbar region, although the length of individual lumbar vertebral bodies varies phylogenetically and possibly allometrically. The other two vertical clingers and leapers, Hapalemur and Lepilemur, more closely resemble the pronograde, quadrupedal taxa. The specialized, suspensory lorids have relatively short lumbar regions as well, but the lengths of their lumbar regions are influenced by body size, and Arctocebus has dramatically longer vertebral bodies than do the other lorids. Lumbar morphology among galagonids appears to reflect a strong phylogenetic signal superimposed on a functional one. In general, relative length of the spinous processes follows a positively allometric trend, although lorids (especially the larger-bodied forms) have relatively short spinous processes for their body size, in accordance with their positional repertoire. The results of the study broaden our understanding of postcranial adaptation in primates, while providing an extensive comparative database for interpreting vertebral morphology in fossil primates.     

Quantitative and functional studies on the hands of the anthropoidea. I. The Hominoidea

The hands of the Hominoidea evidence four adaptive modes which distinguish the lesse apes (Hylobatidae), the orangutan (Pongo), the African apes (Pan), and man (Homo) from one another. The hands of the apes consist of compromises between manipulatory and locomotor functions because selection has operated for precision of grip as well as for special locomotor mechanisms. The human hand is almost totally devoted to manipulation. The hands of gibbons, orangutans and the African apes differ in many features that may be correlated with locomotion. The gibbons and siamang are specially adapted for ricochetal arm-swinging. The great apes possess morphological adaptations for arboreal foraging and climbing distinct from those of the hylobatids. In addition, the African apes have become secondarily adapted for terrestrial quadrupedal locomotion. Many features that distinguish the hands of chimpanzees and gorillas may be associated with the development of efficient knuckele-walking propulsive and support mechanisms.     

Suspensory locomotion of Lagothrix lagothricha and Ateles belzebuth in Yasuní National Park,Ecuador

A comparative field study of the locomotion of woolly monkeys (Lagothrix lagothricha) and spider monkeys (Ateles belzebuth) in undisturbed rainforest of northeastern Ecuador reveals substantial differences in their use of suspensory modes. Ateles performed both more brachiation (by forelimbs and tail, with trunk rotation), and forelimb swing (similar to brachiation, but without trunk rotation) than Lagothrix. In contrast, in Lagothrix 20% of suspensory movement was by pronograde forelimb swing, which resembles forelimb swing except that the body is held in a pronograde orientation due to the tail and/or feet intermittently grasping behind the trailing forelimb. Ateles never exhibited this mode. Both brachiation and forelimb swing by Ateles were more dynamic than in Lagothrix, consisting of higher proportions of full-stride bouts (versus single-step). Both species used smaller supports for suspensory than for quadrupedal locomotion, and Ateles used both smaller and larger supports for suspension than did Lagothrix. Analysis of support inclination shows that both species tended to perform more above-support movement on horizontal supports and more below-support (suspensory) movement from oblique supports. Our attempt to elucidate the aspects of canopy structure that favor suspension suggests the need for additional kinds of observational data, focusing on the "immediate structural context" of positional events.     

The cross-sectional geometry of the hand and foot bones of the hominoidea and its relationship to locomotor behavior

Cheiridia are valuable indicators of positional behavior, as they directly contact the substrate, but systematic comparison of the structural properties of both metacarpals and metatarsals has never been carried out. Differences in locomotor behavior among the great apes (knuckle-walking vs. quadrumanous climbing) can produce biomechanical differences that may be elucidated by the parallel study of cross-sectional characteristics of metacarpals and metatarsals. The aim of this work is to study the cross-sectional geometric properties of these bones and their correlation with locomotor behavior in large-bodied hominoids. The comparisons between bending moments of metacarpals and metatarsals of the same ray furnished interesting results. Metacarpals III and especially IV of the knuckle-walking African apes were relatively stronger than those of humans and orangutans, and metatarsal V of humans was relatively stronger than those of the great apes. Interestingly, the relative robusticity of the metacarpal IV of the quadrumanous orangutan was between that of the African apes and that of humans. The main conclusions of the study are: 1) cross-sectional dimensions of metacarpals and metatarsals are influenced by locomotor modes in great apes and humans; 2) interlimb comparisons of cross-sectional properties of metacarpals and metatarsals are good indicators of locomotor modes in great apes and humans; and 3) the results of this study are in accord with those of previous analyses of plantar pressure and morphofunctional traits of the same bones, and with behavioral studies. These results provide a data base from which it will be possible to compare the morphology of the fossils in order to gain insight into the locomotor repertoires of extinct taxa.     

The correspondence between proximal phalanx morphology and locomotion: implications for inferring the locomotor behavior of fossil catarrhines

Phalanges are considered to be highly informative in the reconstruction of extinct primate locomotor behavior since these skeletal elements directly interact with the substrate during locomotion. Variation in shaft curvature and relative phalangeal length has been linked to differences in the degree of suspension and overall arboreal locomotor activities. Building on previous work, this study investigated these two skeletal characters in a comparative context to analyze function, while taking evolutionary relationships into account. This study examined the correspondence between proportions of suspension and overall substrate usage observed in 17 extant taxa and included angle of curvature and relative phalangeal length. Predictive models based on these traits are reported. Published proportions of different locomotor behaviors were regressed against each phalangeal measurement and a size proxy. The relationship between each behavior and skeletal trait was investigated using ordinary least-squares, phylogenetic generalized least-squares (pGLS), and two pGLS transformation methods to determine the model of best-fit. Phalangeal curvature and relative length had significant positive relationships with both suspension and overall arboreal locomotion. Cross-validation analyses demonstrated that relative length and curvature provide accurate predictions of relative suspensory behavior and substrate usage in a range of extant species when used together in predictive models. These regression equations provide a refined method to assess the amount of suspensory and overall arboreal locomotion characterizing species in the catarrhine fossil record.     

Positional Behavior of Black Spider Monkeys (Ateles paniscus) in French Guiana

Spider monkeys (Ateles) frequently use suspensory locomotion and postures, and their postcranial morphology suggests convergence with extant hominoids in canopy and food utilization. Previous studies of positional behavior in Ateles, have produced variable rates in the use of different positional activities. I investigated the positional behavior of black spider monkeys (Ateles paniscus) in a wet rain forest in French Guiana, and assessed differences in the rates of use of positional modes across studies. I also discuss the significance of suspensory activities in forest utilization. In French Guiana, Ateles confined travel and feeding locomotion on small and medium-sized moderately inclined supports in the main canopy. Tail-arm brachiation and clamber were their main traveling modes, while clamber was the dominant feeding locomotor mode. Small horizontal supports were predominant during their feeding. Suspensory postures accounted for more than half of feeding bouts, with tail-hang and tail-hind limb(s) hang being the dominant postures. Feeding occurred largely in tree crown peripheries with the prehensile tail anchored frequently above the monkey. They usually collected food items below or at the same level as the body. There is no difference among the postures they used to acquire and eat young leaves and fruit. My results agree with reports on the positional behavior of different species of spider monkeys at other sites. Despite the use of different methods, the same species exhibited more or less similar profiles in similar forests. Interspecific differences could be associated with morphological differences. Moreover, intraspecific differences could be attributed to forest structure. The findings suggest that the major part of biological information is independent of methods used in the several studies. Suspensory behavior facilitates the exploitation of the forest canopy by shortening traveling pathways between and within trees, by enabling faster travel for the better exploitation of patchy food sources and by providing access to food in the flexible terminal twigs.     

Major features in the evolution of early hominoid locomotion

Evolution of hominoid locomotion is a traditional topic in primate evolution. Views have changed during the last decade because a number of crucial differences between early and advanced hominoid morphologies have been demonstrated. Increasing evidence on primate behaviour and ecology show that any direct analogies between living and fossil hominoids must be made extremely carefully. The necessity of synthesizing data on primate behaviour, locomotion, morphology and ecology and simultaneously defining the framework in which the data should be interpreted are explained. Results of our studies of ontogeny of locomotor and behavioural patterns (LBP) are presented that could help identify the main features of early hominoid locomotor patterns (LP) and the mechanisms of their changes. The early hominoid LP was different from those of pronograde monkeys and specialized antipronograde living apes. Some similar features could be expected between early hominoid LP and the LP of ceboid monkeys. Analogous mechanisms of change of LBP exist in all groups of living higher primates. Crucial early mechanisms of change are the ontogenetic shifts in LBP connected with ethoecological changes. Analysis of fossil evidence has shown that Miocene hominoids differ morphologically from any group of living primates. Certain features present in Miocene hominoids could be found in Atelinae and living Asian apes but they are limited to some functional regions of the postcrania only. Consequently the early hominoid general LP can not be strictly analogous either to that of any monkey group or to the LP of apes. We suppose that certain pronograde adaptations, such as climbing, bipedality, limited suspensory activity and sitting constituted the main part of their LP.     

Orang-like manual adaptations in the fossil hominoid Hispanopithecus laietanus: first steps towards great ape suspensory behaviours

Morphological and biometrical analyses of the partial hand IPS18800 of the fossil great ape Hispanopithecus laietanus (=Dryopithecus laietanus), from the Late Miocene (about 9.5Ma) of Can Llobateres (Catalonia, Spain), reveal many similarities with extant orang-utans (Pongo). These similarities are interpreted as adaptations to below-branch suspensory behaviours, including arm-swinging and clambering/postural feeding on slender arboreal supports, due to an orang-like double-locking mechanism. This is confirmed by the long and highly curved phalanges of Hispanopithecus. The short and stout metacarpals with dorsally constricted heads, together with the dorsally extended articular facets on proximal phalanges, indicate the persistence of significant degrees of palmigrady. A powerful grasping capability is indicated by the great development of basal phalangeal tubercles, the marked insertions for the flexors on phalangeal shafts and the large pits for the collateral ligaments. The morphology of the Hispanopithecus long bones of the hand indicates a unique positional repertoire, combining orthogrady with suspensory behaviours and palmigrade quadrupedalism. The retention of powerful grasping and palmigrady suggests that the last common ancestor of hominids might have been more primitive than what can be inferred on the basis of extant taxa, suggesting that pronograde behaviours are compatible with an orthograde bodyplan suitable for climbing and suspension.     

Functional morphology of the lemuriform wrist joints and the relationship between wrist morphology and positional behavior in arboreal primates

A comparative study of carpal joint structure and function in six Malagasy lemuriforms was undertaken to test predicted morphoclines in carpal joint morphology between pronograde and orthograde arboreal primates. Patterns of movement at the wrist during locomotion were observed and described for the lemuriform species Lemur fulvus and Propithecus verreauxi. Lemur fulvus, which assumes a pronograde posture during locomotion, extends and pronates the wrist during the support phase of quadrupedal walking and running stride cycles. Furthermore, the forearm of this species exhibits some transverse movement across the proximal wrist joint during the support phase. In contrast, the indriid Propithecus maintains the hand and wrist in a flexed and partially supinated position during vertical clinging and suspensory postures. Habitual quadrupedal and vertical postures in Malagasy primates are in turn related to very different patterns of carpal joint morphology and articular mechanics. Those lemurs which are predominantly pronograde share a series of structural features related to stabilizing the antebrachiocarpal joint during extension and mediolateral deviation and the midcarpal joint during pronation: an intraarticular labrum is present on the inner portion of the radiocarpal ligament, the radiocarpal articular surface is quite flat dorsoventrally, the capitate-trapezoid embrasure is expanded dorsally, and development of the radial and ulnar styloids is more pronounced. The wrists of Propithecus, Avahi, and Lepilemur (vertical clingers) differ from those of quadrupedal lemuriforms in possessing a suite of morphological features related to stabilizing the wrist during antebrachiocarpal flexion and midcarpal supination: the radiocarpal articular surface is deeply curved and tilted anteriorly, the dorsal radiocarpal ligament is very broad, thick, and fibrous, the hamate's triquetral facet is directed proximodistally, and the capitate-trapezoid embrasure is dorsally constricted and expanded palmarly. These observed contrasts in carpal form and function are used to define further the morphological features related to orthograde posture in several lineages of arboreal primates. © 1996 Wiley-Liss, Inc.     

Positional behavior of the white uakari (Cacajao calvus calvus)

The positional behavior and habitat use of a group of white uakaries (Cacajao calvus calvus) was observed for 6 weeks in the dry season at Lake Teiú, Brazil. Data are presented for feeding, traveling, and resting activities. The most common feeding posture is sit, followed by stand. Cacajao frequently exhibits locomotor behaviors while in feeding trees, using pronograde clamber and quadrupedal walk. The most frequently used locomotor behaviors in travel are quadrupedal walk, leap, and pronograde clamber. Quadrupedal run and drop also figure importantly in the behavioral repertoire. The most frequent resting posture was sit, followed by ventral lie. Compared to representative members of the other pitheciin genera, Pithecia and Chiropotes, Cacajao engages in more locomotion while feeding, and uses more pedal suspension. While traveling, pronograde clamber and drop are more frequently used by Cacajao. Multiple, deformable supports are used more by Cacajao than by the other pitheciins throughout all activities. Overall, the positional behavior of Cacajao is more similar to that of Chiropotes than of Pithecia. Cacajao's behavioral solutions to the problems of balance imposed by its greatly reduced tail are discussed. © 1996 Wiley-Liss, Inc.     

Postcranial functional morphology of Morotopithecus bishopi, with implications for the evolution of modern ape locomotion

The large-bodied hominoid from Moroto, Uganda has until recently been known only from proconsulid like craniodental remains and some vertebrae with modern ape like features. The discovery of two partial femora and the glenoid portion of a scapula demonstrates that the functional anatomy of Morotopithecus differed markedly from other early and middle Miocene hominoids. Previous studies have consistently associated the vertebral remains with a short, stiff back and with orthograde postures. Although the proximal femur more closely resembles the femora of monkeys than of apes and suggests a moderate degree of hip abduction, the distal femur resembles those of extant large bodied apes and suggests a varied loading regime and an arboreal repertoire that may have included substantial vertical climbing. The femoral shaft displays uniformly thick cortical bone, beyond the range of thickness seen in extant primates, and signifies higher axial loading than is typical of most extant primates. The glenoid fossa is broad and uniformly curved as in extant suspensory primates. Overall, Morotopithecus is reconstructed as an arboreal species that probably relied on forelimb-dominated, deliberate and vertical climbing, suspension and quadrupedalism. Morotopithecus thus marks the first appearance of certain aspects of the modern hominoid body plan by at least 20 Ma. If the suspensory and orthograde adaptations linking Morotopithecus to extant apes are synapomorphies, Morotopithecus may be the only well-documented African Miocene hominoid with a close relationship to living apes and humans.