THE LOCOMOTION OF THE LORISES,WITH SPECIAL REFERENCE TO THE POTTO

The stealthy locomotion of the lorises is seen to be directly related to catching prey such as insects and roosting birds. The method of stalking prey contrasts strongly with the quick leaping method of food-catching presented by the galagos. The lorises, by virtue of their food-catching habits, are restricted to true forest, whereas some of the galagos, by the same token, have colonized more open country. This throws some light on the nature of the post-Miocene link between Africa and Asia and is suggested as a reason why the galagos are restricted to Africa whereas the lorises are found in both Africa and Asia.     

Home Range Analysis of <Emphasis Type="Italic">Perodicticus potto edwardsi</Emphasis> and <Emphasis Type="Italic">Sciurocheirus cameronensis</Emphasis>

Because the spatial arrangements of nocturnal prosimians are often used to indicate their social systems, it is important to assess the reliability of methods used to analyze ranging patterns. We compared methods of home range analysis for 2 species of nocturnal prosimians: central pottos (Perodicticus potto edwardsi) and Cross River Allens galagos ({Sciurocheirus cameronensis}). We conducted radio-tracking studies of 10 pottos and 8 galagos from October 1999 – November 2000 in the montane rain forests of southwest Cameroon. We calculated home ranges via minimum convex polygon (MCPs) and kernel analyses. Adult potto home ranges averaged 145.2 ha (MCPs) versus only 28.4 ha via kernel analysis; the difference is statistically significant. The mean home range of galagos is 18.3 ha via MCPs and 2.19 ha via kernel analysis; the difference is statistically significant. Neither MCP nor kernel analyses revealed a sex difference in adult home ranges for pottos and galagos. Kernel analysis gave more reliable estimates of home ranges than the minimum convex polygon method used in many studies of nocturnal prosimians. Minimum convex polygon analysis tended to overestimate the range sizes and to include many areas not traversed by the animal. We compared our findings with those from an earlier study of similar species in Gabon, where little attention was given to the home range analysis, technique. Together with studies of lemur spatial systems they highlight the importance of considering the method of home range analysis when it is to be applied to understanding social systems.     

Body weight: its relation to tissue composition, segment distribution, and motor function. II. Development of Macaca mulatta.

The relative composition of skin, muscle, and bone and their distribution patterns throughout the body are given for a series of Macaca mulatta from 171 days conceptual age through adulthood. In terms of percent of total body weight, the musculature of these animals doubles during the firs postnatal year whereas bone and skin decrease. Regionally, the muscles of the thighs, back extensors, truncal-forelimb and upper arms increase most markedly. The thighs double and the upper arms increase whereas the trunk, hands, feet, and tail decrease. The biomechanical implications of these changes for motor development are discussed.     

Effects of animate vs. inanimate stimuli on curiosity behavior in greater galago and slow loris

Captive prosimians housed in a semi-natural laboratory environment were exposed to novel stimuli, both animate (cat, snake) and inanimate (empty box). Observations were made by means of closed circuit TV. Animate stimuli elicited considerably more interest (about 42% of a test session) than the inanimate stimulus (about 12% of the test session). The more vulnerable species, the slow loris, displayed as much curiosity as the less vulnerable species, the greater galago; but, in the presence of live stimuli, lorises were more cautious. They moved slowly and silently, employed contact as a mode of investigation significantly less often than galagos, spent significantly less time than galagos investigating from within 3 ft, took significantly longer than galagos to make their first approaches to within the 3 ft zone, and, once there, stayed for significantly shorter visits than galagos. The data demonstrate: (1) that prosimians are highly responsive to novelty if the stimuli are appropriate; and (2) that it is important to take into account not just whether animals investigate but also how they investigate.     

A Survey of Husbandry Practices for Lorisid Primates in North American Zoos and Related Facilities

Zoos and related facilities in North America currently manage five species in the primate family Lorisidae: the greater (Nycticebus coucang), Bengal (N. bengalensis) and pygmy (N. pygmaeus) slow lorises, red slender loris (Loris tardigradus), and potto (Perodicticus potto). We used an online survey to describe institutional housing and husbandry practices for these species and assess the extent to which practices are consistent with established guidelines. Our results show that most captive lorisids are housed solitarily or in pairs. Most individuals occupy a single exhibit space in a building dedicated to nocturnal animals. Facilities are commonly meeting recommendations for abiotic exhibit design and are providing animals with an enriched environment. However, pottos and slender lorises currently occupy exhibit spaces smaller than the recommended minimum, and the impact of cleaning protocols on olfactory communication should be critically evaluated. Few facilities are taking advantage of the benefits of positive reinforcement training for promoting animal welfare. Research is greatly needed on the effects of exhibit lighting on behavior, health, and reproduction; and to determine how best to manage the social needs of lorisids with naturally dispersed social structures. Although captive populations of slender lorises, pottos, and slow lorises are declining, we suggest that improved husbandry knowledge has the potential to positively influence population sustainability and to enhance future efforts to manage the growing pygmy loris population. Zoo Biol. 32:88‐100, 2013. © 2012 Wiley Periodicals, Inc.     

Mandibular corpus strain in primates: Further evidence for a functional link between symphyseal fusion and jaw-adductor muscle force

Previous work indicates that compared to adult thick-tailed galagos, adult long-tailed macaques have much more bone strain on the balancing-side mandibular corpus during unilateral isometric molar biting (Hylander [1979a] J. Morphol. 159:253–296). Recently we have confirmed in these same two species the presence of similar differences in bone-strain patterns during forceful mastication. Moreover, we have also recorded mandibular bone strain patterns in adult owl monkeys, which are slightly smaller than the galago subjects. The owl monkey data indicate the presence of a strain pattern very similar to that recorded for macaques, and quite unlike that recorded for galagos. We interpret these bone-strain pattern differences to be importantly related to differences in balancing-side jaw-adductor muscle force recruitment patterns. That is, compared to galagos, macaques and owl monkeys recruit relatively more balancing-side jaw-adductor muscle force during forceful mastication. Unlike an earlier study (Hylander [1979b] J. Morphol. 160:223–240), we are unable to estimate the actual amount of working-side muscle force relative to balancing-side muscle force (i.e., the W/ B muscle force ratio) in these species because we have no reliable estimate of magnitude, direction, and precise location of the bite force during mastication. A comparison of the mastication data with the earlier data recorded during isometric molar biting, however, supports the hypothesis that the two anthropoids have a small W/ B jaw-adductor muscle force ratio in comparison to thick-tailed galagos. These data also support the hypothesis that increased recruitment of balancing-side jaw-adductor muscle force in anthropoids is functionally linked to the evolution of symphyseal fusion or strengthening. Moreover, these data refute the hypothesis that the recruitment pattern differences between macaques and thick-tailed galagos are due to allometric factors. Finally, although the evolution of symphyseal fusion in primates may be linked to increased stress associated with increased balancing-side muscle force, it is currently unclear as to whether the increased force is predominately vertically directed, transversely directed, or is a near equal combination of these two force components (cf. Ravosa and Hylander [1994] In Fleagle and Kay [eds.]: Anthropoid Origins. New York: Plenum, pp. 447–468). Am J Phys Anthropol 107:257-271, 1998. © 1998 Wiley-Liss, Inc.     

Growth and the development of sexual size dimorphism in lorises and galagos

Three fundamental ontogenetic pathways lead to the development of size differences between males and females. Males and females may grow at the same rate for different durations (bimaturism), grow for the same duration at different rates, or grow at a mix of rate and duration differences. While patterns of growth and the development of adult body size are well established for many haplorhines, the extent to which rate and duration differences affect strepsirrhine growth trajectories remains unclear. Here, we present iterative piecewise regression models that describe the ontogeny of adult body mass for males and females of five lorisoid species (i.e., lorises and galagos) from the Duke Lemur Center. We test the hypotheses that, like most haplorhines, sexual size dimorphism (SSD) is a result of bimaturism, and males and females of monomorphic species grow at the same rate for a similar duration. We confirm that the galagos in this sample (Galago moholi and Otolemur garnettii) show significant SSD that is achieved through bimaturism. Unlike monomorphic lemurids, the lorises in this sample show a diversity of ontogenetic patterns. Loris tardigradus does follow a lemur-like trajectory to monomorphism but Nycticebuscoucang and Nycticebus pygmaeus achieve larger adult female body sizes through a mixture of rate and duration differences. We show that contrary to previous assumptions, there are patterns of both similarity and difference in growth trajectories of comparably sized lorises and galagos. Furthermore, when ontogenetic profiles of lorisoid and lemurid growth are compared, it is evident that lorisoids grow faster for a shorter period of time.     

Mandibular function in Galago crassicaudatus and Macaca fascicularis: an in vivo approach to stress analysis of the mandible.

Single-element and/or rosette strain gages were bonded to mandibular cortical bone in Galago crassicaudatus and Macaca fascicularis. Five galago and eleven macaque bone strain experiments were performed and analyzed. In vivo bone strain was recorded from the lateral surface of the mandibular corpus below the postcanine tooth row during transducer biting and during mastication and ingestion of food objects. In macaques and galagos, the mandibular corpus on the balancing side is primarily bent in the sagittal plane during mastication and is both twisted about its long axis and bent in the sagittal plane during transducer biting. On the working side, it is primarily twisted about its long axis and directly sheared perpendicular to its long axis, and portions of it are bent in the sagittal plane during mastication and molar transducer biting. In macaques, the mandibular corpus on each side is primarily bent in the sagittal plane and twisted during incisal transducer biting and ingestion of food objects, and it is transversely bent and slightly twisted during jaw opening. Since galagos usually refused to bite the transducer or food objects with their incisors, an adequate characterization of mandibular stress patterns during these behaviors was not possible. In galagos the mandibular corpus experiences very little transverse bending stress during jaw opening, perhaps in part due to its unfused mandibular symphysis. Marked differences in the patterns of mandibular bone strain were present between galagos and macaques during the masticatory power stroke and during transducer biting. Galagos consistently had much more strain on the working side of the mandibular corpus than on the balancing side. These experiments support the hypothesis that galagos, in contrast to macaques, employ a larger amount of working-side muscle force relative to the balancing-side muscle force during unilateral biting and mastication, and that the fused mandibular symphysis is an adaption to use a maximal amount of balancing-side muscle force during unilateral biting and mastication. These experiments also demonstrate the effects that rosette position, bite force magnitudes, and types of food eaten have on recorded mandibular strain patterns.     

Symphyseal fusion and jaw-adductor muscle force: an EMG study

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. (ABSTRACT TRUNCATED)     

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.     

The functional significance of primate mandibular form.

A stress analysis of the primate mandible suggests that vertically deep jaws in the molar region are usually an adaptation to counter increased sagittal bending stress about the balancing-side mandibular corpus during unilateral mastication. This increased bending stress about the balancing side is caused by an increase in the amount of balancing-side muscle force. Furthermore, this increased muscle force will also cause an increase in dorso-ventral shear stress along the mandibular symphysis. Since increased symphyseal stress can be countered by symphyseal fusion and as increased bending stress can be countered by a deeper jaw, deep jaws and symphyseal fusion are often part of the same functional pattern. In some primates (e.g., Cercocebus albigena), deep jaws are an adaptation to counter bending in the sagittal plane during powerful incisor biting, rather than during unilateral mastication. The stress analysis of the primate mandible also suggests that jaws which are transversely thick in the molar region are an adaptation to counter increased torsion about the long axis of the working-side mandibular corpus during unilateral mastication. Increased torsion of the mandibular corpus can be caused by an increase in masticatory muscle force, an increase in the transverse component of the postcanine bite force and/or an increase in premolar use during mastication. Patterns of masticatory muscle force were estimated for galagos and macaques, demonstrating that the ratio of working-side muscle force to balancing-side muscle force is approximately 1.5:1 in macaques and 3.5:1 in galagos during unilateral isometric molar biting. These data support the hypothesis that mandibular symphyseal fusion is an adaptative response to maximize unilateral molar bite force by utilizing a greater percentage of balancing-side muscle force.     

Tale of tails: parallelism and prehensility

The occurrence of prehensile tails among only five platyrrhine genera--Cebus, Alouatta, Lagothrix, Ateles, and Brachyteles--might be interpreted as evidence that these are a closely related, possibly monophyletic group. In the absence of behavioral data, it is impossible to test whether all possess equivalent biological roles; such would lend credence to the idea that their tails evolved from an homologous, derived character complex. Contrariwise, the tendency for species of Cebus to have "averagely" proportioned or relatively short tails, in contrast to the relatively elongate tails of howlers and other atelines; osteological differences in caudal and sacral morphology; and a lack of ateline-like tail/neocortex correlates in Cebus, all imply that prehensility has evolved twice in parallel: once (homologously) in atelines and again in capuchins.     

Genetics analysis of mouse mutations Abnormal feet and tail and rough coat, which cause developmental abnormalities and alopecia

Mutations in the mouse Brachyury (T) gene are characterized by a dominant reduction of tail length and recessive lethality. Two quantitative trait loci, Brachyury-modifier 1 and 2 (Brm1 and Brm2) are defined by alleles that enhance the short-tail Brachyury phenotype. Here we report on a genetic analysis of a visible dominant mutation Abnormal feet and tail (Aft) located in the vicinity of Brm1. Affected animals display kinky tails and syndactyly in the hindlimbs, both likely resulting from a defect in apoptosis. We observed an unusual genetic incompatibility between Aft and certain genetic backgrounds. We show that Aft and T are likely to interact genetically, since some double heterozygotes are tailless. In addition to the tail and hindlimb phenotypes, Aft-bearing mutants display characteristic late-onset skin lesions. We therefore tested for allelism between Aft and a closely linked recessive mutation rough coat (rc) and found that these two mutations are likely nonallelic. Our results provide a valuable resource for the study of mammalian skin development and contribute to the genetic analysis of Brachyury function.     

The role of grafted skin in the regeneration of X-irradiated axolotl limbs

The primary aim of these experiments was to follow the cells descended from limb skin through the process of limb regeneration to determine what range of differentiations these cells may assume. Triploid hindlimb or forelimb skin was grafted to the denuded thighs of diploid host axolotls that had previously received 3000 R of X irradiation across both hindlimbs and the intervening pelvic area. The host limbs were then amputated through their grafts and permitted to regenerate. Cartilage, perichondrium, joint connective tissue, general connective tissue, dermis, and epidermis were present in all the regenerated limbs, but only 10% of the regenerates contained muscle. Tabulation of nucleolar numbers showed that the majority of cells in each regenerated tissue originated from the grafted skin. A strong correlation was demonstrated between the forelimb or hindlimb origin of the skin grafts and the number of digits regenerated.     

Activity budget and positional behavior of the Mysore slender loris (Loris tardigradus lydekkerianus): implications for slow climbing locomotion.

Both predator defense and feeding ecology models have been proposed to explain the relatively slow climbing locomotion of the Lorisinae. During a study of the socioecology of the Mysore slender loris (Loris tardigradus lydekkerianus) in Tamil Nadu, India, six categories of behavior and eleven different postures were recorded to estimate a general activity budget for the slender loris, and are examined here particularly in relation to slow climbing locomotor strategies. Reactions to potential predators are also described. The main study population was composed of 15 animals. Activity budgets were compiled in three ways: all instantaneous point samples collected over 1,173 h pooled (n = 13,717), the means of individual lorises (n = 15) and behavior at the moment of first contact (n = 357). No significant difference was found between these three data sets. Approximately 45% of the activity budget was spent in inactive behaviors including sitting vigilant, resting and sleeping. Foraging and traveling comprised nearly half the activity budget, with the rest of the time spent grooming. The most common postures assumed by lorises were sitting and quadrupedal walking. Individual lorises were relatively gregarious and spent up to half their activity budget with other animals. Unlike pottos and angwantibos, lorises did not freeze, head butt or drop from branches in reaction to potential predators, but either ignored them, fled or made loud calls. Cryptic and slow climbing locomotion were used before traveling on open ground between discontinuous substrates, thereby supporting hypotheses relating to predator pressure, and also before capturing fast moving insect prey, supporting hypotheses relating to diet. It is proposed that a divergence in foraging strategies between bushbabies and lorisines may be the best adaptive explanation for their behavioral and morphological differences, including predator defense mechanisms.     

Development of a laboratory line (SRI line) derived from the wild house musk shrew, Suncus murinus, indigenous to Sri Lanka

Five male and 9 female house musk shrews (Suncus murinus) captured in Koralawella, Sri Lanka were acquired by our laboratory. One male and 3 females alone contributed to the development of a new laboratory line (SRI line). The SRI line has been maintained as a closed breeding colony consisting of more than 40 shrews. Gestation period and litter size at birth averaged 31.2 days (43 cases) and 2.4 (43 litters), respectively. The SRI line shrews were uniformly covered with light gray fur. The body weight and total length of adult shrews averaged 72.9 g and 23.9 cm in males, and 49.6 g and 21.0 cm in females. These data indicate a body size intermediate between BAN line shrews originating from Bangladesh and Nag or OKI line shrews from Japan. The SRI shrews are also characterized by having 30 chromosomes in diploid, being the smallest number in the entire species, whereas the otherlines (Nag, OKI and BAN) all have 40 chromosomes.     

An ethmoid exposure (os planum) in the orbit of Indri indri (Primates, Lemuriformes).

In 6 of 17 skulls of Indri indri retaining distinct sutures in the medial orbital wall, a small separate bony element intervenes between the frontal and the maxillolacrimal suture. This element is demonstrably continuous with the ethmoid on one such skull. The occurrence of an ethmoid exposure in the orbit of Indri suggests that this trait is not a simple function of orbital size and convergence. Since such an exposure is found in non-cheirogaleine lemuriforms, its distribution provides no support for the hyothesis that lorises and galagos are derived from cheirogaleines.     

The musculoskeletal anatomy of the reindeer (Rangifer tarandus): fore- and hindlimb

Reindeer are numerous and widespread across the northern Holarctic. They are efficient long distance migrants and are able to cope with variations in substrate, such as ice, snow, uneven forest floor, wetland and flat grassland. However, as with the vast majority of quadrupedal vertebrates, no quantitative musculoskeletal anatomical information exists for these animals making it difficult to analyse the biomechanics of their locomotor behaviour. In this paper, we describe the gross anatomy of the limb musculature and quantify muscle and tendon morphology. Reindeer show slight hindlimb dominance in muscle and tendon mass, with muscle mass primarily proximally situated and tendon distally situated. Extensor muscles are heavier than flexors, but tendon mass is broadly similar in both extensors and flexors. The only complete quadrupedal data sets available for comparison are for hares and greyhounds making it difficult to identify general patterns. There are no obvious body mass effects and reindeer often comes out as intermediate between hare and greyhound. However, greyhound seem less hindlimb dominated in terms of muscle but both greyhound and hare have much higher masses of tendon compared to reindeer, particularly in their hindlimbs. All these quadrupeds show the commonly observed trait of much larger tendons and less massive muscles in distal limb segments; this reduces the inertial cost of accelerating the limbs. Generally, there is a dearth of available quantitative anatomical data of complete animals. This lack of information is hindering attempts to gain a better understanding of musculoskeletal function in quadrupeds.     

Locomotor mechanics of the slender loris (Loris tardigradus)

The quadrupedal walking gaits of most primates can be distinguished from those of most other mammals by the presence of diagonal-sequence (DS) footfall patterns and higher peak vertical forces on the hindlimbs compared to the forelimbs. The walking gait of the woolly opossum (Caluromys philander), a highly arboreal marsupial, is also characterized by diagonal-sequence footfalls and relatively low peak forelimb forces. Among primates, three species--Callithrix, Nycticebus, and Loris--have been reported to frequently use lateral-sequence (LS) gaits and experience relatively higher peak vertical forces on the forelimbs. These patterns among primates and other mammals suggest a strong association between footfall patterns and force distribution on the limbs. However, current data for lorises are limited and the frequency of DS vs. LS walking gaits in Loris is still ambiguous. To test the hypothesis that patterns of footfalls and force distribution on the limbs are functionally linked, kinematic and kinetic data were collected simultaneously for three adult slender lorises (Loris tardigradus) walking on a 1.25 cm horizontal pole. All subjects in this study consistently used diagonal-sequence walking gaits and always had higher peak vertical forces on their forelimbs relative to their hindlimbs. These results call into question the hypothesis that a functional link exists between the presence of diagonal-sequence walking gaits and relatively higher peak vertical forces on the hindlimbs. In addition, this study tested models that explain patterns of force distribution based on limb protraction angle or limb compliance. None of the Loris subjects examined showed kinematic patterns that would support current models proposing that weight distribution can be adjusted by actively shifting weight posteriorly or by changing limb stiffness. These data reveal the complexity of adaptations to arboreal locomotion in primates and indicate that diagonal-sequence walking gaits and relatively low forelimb forces could have evolved independently.