Kinematics of bipedal locomotion while carrying a load in the arms in bearded capuchin monkeys (Sapajus libidinosus)

Stone Tool Use by Black-Horned Capuchin Monkeys (Sapajus nigritus cucullatus) in an Urban Park in Londrina, Brazil

Tool use to crack open palm nuts has been observed extensively in some capuchin monkey species. However, for southern black-horned capuchin monkeys (Sapajus nigritus cucullatus), there is only one published record of stone tool use from the 1990s, from an urban park in Londrina, Brazil. In the present study, we returned to this urban park to systematically investigate the hammer-and-anvil sites used to crack nuts by this capuchin monkey population. We analyzed the fruit and shell remnants resulting from hammering to test the following hypotheses: (1) hammers at tool-use sites are actively chosen for size and/or weight, (2) tool use sites that are closer to a tree of the processed plant species are more frequently used, and (3) there is no seasonal effect modulating hammer-and-anvil use for processing nuts. We located and identified 205 tool-use sites through active search within the park, and we measured and weighed the tools involved in hammering activity. We compared hammer weight and size to that of the comparable material available in the environment and found that hammer size and weight differed significantly from that of the raw materials found in the environment, suggesting active choice of the hammers. We identified three plant species for which nuts were processed through tool use: Syagrus romanzoffiana, Acrocomia aculeata and Terminalia catappa. Through measuring the distance between each tool-use site and the nearest tree of the plant species processed there, we found that closer proximity between the tool-use site and the nearest target tree (Syagrus and Acrocomia) increased cracking frequency. We returned to each site three times during the study year to determine if new tool use activity had occurred, and our data indicate habitual use of tools to crack open nuts throughout the year, with no large differences between seasons.

Bearded capuchin monkeys use joint synergies to stabilize the hammer trajectory while cracking nuts in bipedal stance

The transition from occasional to obligate bipedalism is a milestone in human evolution. However, because the fossil record is fragmentary and reconstructing behaviour from fossils is difficult, changes in the motor control strategies that accompanied this transition remain unknown. Quadrupedal primates that adopt a bipedal stance while using percussive tools provide a unique reference point to clarify one aspect of this transition, which is maintaining bipedal stance while handling massive objects. We found that while cracking nuts using massive stone hammers, wild bearded capuchin monkeys (Sapajus libidinosus) produce hammer trajectories with highly repeatable spatial profiles. Using an uncontrolled manifold analysis, we show that the monkeys used strong joint synergies to stabilize the hammer trajectory while lifting and lowering heavy hammers. The monkeys stringently controlled the motion of the foot. They controlled the motion of the lower arm and hand rather loosely, showing a greater variability across strikes. Overall, our findings indicate that while standing bipedally to lift and lower massive hammers, an arboreal quadrupedal primate must control motion in the joints of the lower body more stringently than motion in the joints of the upper body. Similar changes in the structure of motor variability required to accomplish this goal could have accompanied the evolutionary transition from occasional to obligate bipedalism in ancestral hominins.

GAIT DIVISION OF HEALTHY AND SPINAL CORD–INJUREDRHESUS MONKEYSBY ONE-DIMENSIONAL TOE SIGNALS

Spinal cord injury (SCI) may cause disastrous damage to human locomotion and ultimately make patients suffer from gait anomaly. In the extensive SCI research, the locomotion function serves as a vital standard not only for revealing the underlying SCI mechanism but also for evaluating the clinical therapy. Gait division is the basis of gait analysis. Calculation of gait parameters is available for locomotion function evaluation only when gait cycles are accurately divided. Based on the characteristics of stride height, which is defined as the real-time height of toes vertical to the running direction of a treadmill belt, this study presented three automatic gait division methods, divided the gait cycles for healthy and spinal cord-injured rhesus monkeys, established the evaluation standards, and made comparison of these three methods. For the healthy, injured and mixed groups, the overall accuracies of these three methods were respectively 0.871[Formula: see text][Formula: see text][Formula: see text]0.223, 0.570[Formula: see text][Formula: see text][Formula: see text]0.372, and 0.720[Formula: see text][Formula: see text][Formula: see text]0.339 (method 1); 0.658[Formula: see text][Formula: see text][Formula: see text]0.245, 0.737[Formula: see text][Formula: see text][Formula: see text]0.206, and 0.698[Formula: see text][Formula: see text][Formula: see text]0.228 (method 2); 0.966[Formula: see text][Formula: see text][Formula: see text]0.060, 0.759[Formula: see text][Formula: see text][Formula: see text]0.343, and 0.863[Formula: see text][Formula: see text][Formula: see text]0.265 (method 3). The results show that the stride height characteristics combined with the filter technique may help realize the adequate gait division.

Influence of walking speed on gait parameters of bipedal locomotion in rhesus monkeys

BACKGROUND

The primate model of bipedal locomotion has been extensively used to study human evolution and played a critical role in exploring the pathological mechanisms of human neurologic disease and spinal cord injury. Speed has great influence on both walking posture and gait parameters in human walking; however, how speed changes the gait pattern of bipedal locomotion in primates remains unclear.

METHODS

We chose six adult female rhesus monkeys (Macaca mulatta) and collected the gait parameters of these animals during their treadmill locomotion over a wide range of speed. Using a 3D motion analysis system, we studied the spatiotemporal characteristics of the gait pattern.

RESULTS AND CONCLUSIONS

We have built an efficient and time-saving primate model and shown that speed significantly impacts kinematic parameters. This may present a thorough description of speed-related changes in the gait pattern of rhesus and shed light on the control of bipedal locomotion in primates.

Vertical bipedal locomotion in wild bearded capuchin monkeys (Sapajus libidinosus)

When carrying objects, nonhuman primates often show bipedal locomotion. Studies of primate bipedality, however, in both nature and captivity, have concentrated on locomotion on horizontal substrates, either terrestrially or arboreally. No observational or experimental study seems to have looked at non-horizontal bipedality, yet we show here that it occurs often in nature in Sapajus libidinosus, the bearded capuchin monkey. The context is transport of small food items from source to site of consumption, in which the monkeys usually carry handfuls of maize kernels over several meters' distance, both on the ground and in the trees. Most impressively, over a fifth of such bouts are done vertically, when the tree trunk is fully upright. Such vertical bipedality, with or without transport, apparently has not been reported before.

Percussive tool use by Taï Western chimpanzees and Fazenda Boa Vista bearded capuchin monkeys: a comparison

Percussive tool use holds special interest for scientists concerned with human origins. We summarize the findings from two field sites, Taï and Fazenda Boa Vista, where percussive tool use by chimpanzees and bearded capuchins, respectively, has been extensively investigated. We describe the ecological settings in which nut-cracking occurs and focus on four aspects of nut-cracking that have important cognitive implications, namely selection of tools, tool transport, tool modification and modulation of actions to reach the goal of cracking the nut. We comment on similarities and differences in behaviour and consider whether the observed differences reflect ecological, morphological, social and/or cognitive factors. Both species are sensitive to physical properties of tools, adjust their selection of hammers conditionally to the resistance of the nuts and to transport distance, and modulate the energy of their strikes under some conditions. However, chimpanzees transport hammers more frequently and for longer distances, take into account a higher number of combinations of variables and occasionally intentionally modify tools. A parsimonious interpretation of our findings is that morphological, ecological and social factors account for the observed differences. Confirmation of plausible cognitive differences in nut-cracking requires data not yet available.

Comparative anatomy of the hind limb vessels of the bearded capuchins (Sapajus libidinosus) with apes, baboons, and Cebus capucinus: with comments on the vessels' role in bipedalism

Capuchin monkeys are known to exhibit sporadic bipedalism while performing specific tasks, such as cracking nuts. The bipedal posture and locomotion cause an increase in the metabolic cost and therefore increased blood supply to lower limbs is necessary. Here, we present a detailed anatomical description of the capuchin arteries and veins of the pelvic limb of Sapajus libidinosus in comparison with other primates. The arterial pattern of the bearded capuchin hind limb is more similar to other quadrupedal Cebus species. Similarities were also found to the pattern observed in the quadruped Papio, which is probably due to a comparable pelvis and the presence of the tail. Sapajus' traits show fewer similarities when compared to great apes and modern humans. Moreover, the bearded capuchin showed unique patterns for the femoral and the short saphenous veins. Although this species switches easily from quadrupedal to bipedal postures, our results indicate that the bearded capuchin has no specific or differential features that support extended bipedal posture and locomotion. Thus, the explanation for the behavioral differences found among capuchin genera probably includes other aspects of their physiology.

Self-generated sounds of locomotion and ventilation and the evolution of human rhythmic abilities

It has been suggested that the basic building blocks of music mimic sounds of moving humans, and because the brain was primed to exploit such sounds, they eventually became incorporated in human culture. However, that raises further questions. Why do genetically close, culturally well-developed apes lack musical abilities? Did our switch to bipedalism influence the origins of music? Four hypotheses are raised: (1) Human locomotion and ventilation can mask critical sounds in the environment. (2) Synchronization of locomotion reduces that problem. (3) Predictable sounds of locomotion may stimulate the evolution of synchronized behavior. (4) Bipedal gait and the associated sounds of locomotion influenced the evolution of human rhythmic abilities. Theoretical models and research data suggest that noise of locomotion and ventilation may mask critical auditory information. People often synchronize steps subconsciously. Human locomotion is likely to produce more predictable sounds than those of non-human primates. Predictable locomotion sounds may have improved our capacity of entrainment to external rhythms and to feel the beat in music. A sense of rhythm could aid the brain in distinguishing among sounds arising from discrete sources and also help individuals to synchronize their movements with one another. Synchronization of group movement may improve perception by providing periods of relative silence and by facilitating auditory processing. The adaptive value of such skills to early ancestors may have been keener detection of prey or stalkers and enhanced communication. Bipedal walking may have influenced the development of entrainment in humans and thereby the evolution of rhythmic abilities.