Electromyography of knuckle-walking: results of four experiments on the forearm of Pan gorilla

Preliminary results of electromyographic (EMG) studies on the forearm of a gorilla provisionally support the hypothesis that special closepacked positioning mechanisms may characterize the wrist and metacarpophalangeal joints II–V in extant knuckle-walkers (chimpanzees and gorillas). We recommend that once the bony features, related to these close-packed positions are clearly identified, they may be employed strategically to discern evidence of a knuckle-walking heritage in the hands of extant hominoids, including man, and to trace the history of knuckle-walking in available fossils. This report contains results of the first successful employment of indwelling fine-wire electrode techniques to elucidate problems on the functional and evolutionary biology of great apes.     

四种灵长类肘关节的生物力学研究

对懒猴、猕猴、叶猴和长臂猿的肘关节形态与功能和前臂伸、屈肌肌肉电生理的研究结果表明,随着上肢运动功能的加强,肘关节的灵活性亦相应增大。猕猴各肌的肌电活动相对较弱,肘关节的结构明显不同于其它3个种,表现出对四足型运动和维持关节稳定性的适应特点。叶猴肘关节的形态结构和前臂各肌的肌电活动类似于长臂猿,表现出与臂摆荡有关的活动特点。对前臂伸、屈肌有关指数的判别分析表明,与骨骼相比,4个种的前臂各肌的形态差异明显较大。肱肌的近侧起点指数。肱桡肌的止点指数和肱三头肌内侧头的起点指数可作为4个种的鉴定特征。     

The lorisiform wrist joint and the evolution of "brachiating" adaptations in the hominoidea.

In lorisines (Loris, Nycticebus, Perodicticus, Arctocebus), the tip of the ulna is reduced to the dimensions of a styloid process, a new and more proximal ulnar head is developed, and the pisiform is displaced distally away from its primitive contact with the ulna. In some Nycticebus, intra-articular tissues separate the ulna from the triquetrum. These traits are not seen in other quadrupedal primates, but they are characteristic of extant hominoids. Among hominoids, these features have been interpreted as adaptations to arm-swinging locomotion. Since hominoid-like features of the wrist joint are found in lorisines, but not in New World monkeys that practice arm-swinging locomotion, these features may have been evolved in both lorisines and large hominoids to enhance wrist mobility for cautious arboreal locomotion involving little or no leaping. Most of the other morphological traits characteristic of modern hominoids can be explained as adaptations to cautious quadrupedalism as well as to brachiation, and may have developed for different reasons in different lineages descended from an unspecialized cautious quadruped resembling Alouatta.     

Metacarpal head biomechanics: a comparative backscattered electron image analysis of trabecular bone mineral density in Pan troglodytes, Pongo pygmaeus, and Homo sapiens

Great apes and humans use their hands in fundamentally different ways, but little is known about joint biomechanics and internal bone variation. This study examines the distribution of mineral density in the third metacarpal heads in three hominoid species that differ in their habitual joint postures and loading histories. We test the hypothesis that micro-architectural properties relating to bone mineral density reflect habitual joint use. The third metacarpal heads of Pan troglodytes, Pongo pygmaeus, and Homo sapiens were sectioned in a sagittal plane and imaged using backscattered electron microscopy (BSE-SEM). For each individual, 72 areas of subarticular cortical (subchondral) and trabecular bone were sampled from within 12 consecutive regions of the BSE-SEM images. In each area, gray levels (representing relative mineralization density) were quantified.Results show that chimpanzee, orangutan, and human metacarpal III heads have different gray level distributions. Weighted mean gray levels (WMGLs) in the chimpanzee showed a distinct pattern in which the ‘knuckle-walking’ regions (dorsal) and ‘climbing’ regions (palmar) are less mineralized, interpreted to reflect elevated remodeling rates, than the distal regions. Pongo pygmaeus exhibited the lowest WMGLs in the distal region, suggesting elevated remodeling rates in this region, which is loaded during hook grip hand postures associated with suspension and climbing. Differences among regions within metacarpal heads of the chimpanzee and orangutan specimens are significant (Kruskal–Wallis, p < 0.001). In humans, whose hands are used for manipulation as opposed to locomotion, mineralization density is much more uniform throughout the metacarpal head. WMGLs were significantly (p < 0.05) lower in subchondral compared to trabecular regions in all samples except humans. This micro-architectural approach offers a means of investigating joint loading patterns in primates and shows significant differences in metacarpal joint biomechanics among great apes and humans.     

Curvature of the forelimb bones of anthropoid primates: Overall allometric patterns and specializations in suspensory species

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

A five-link 2D brachiating ape model with life-like zero-energy-cost motions

We have found periodic life-like brachiating motions of a rigid-body ape model that use no muscle or gravitational energy to move steadily forward. The most complicated of these models has 5 links (a body and two arms, each with 2 links) and 7 degrees of freedom in flight. The defining feature of all our periodic solutions is that all collisions are at zero relative velocity. These motions are found using numerical integration and root-finding that is sufficiently precise so as to imply that the solutions found correspond to mathematical solutions with exactly zero energy cost. The only actuation and control in the model is for maintaining contact with and releasing handholds which requires no mechanical work. The similarity of these energy-free simulations to the motions of apes suggests that muscle-use minimization at least partially characterizes the coordination strategies they use.     

Positional behavior of Pan troglodytes in the Mahale Mountains and Gombe Stream National Parks, Tanzania.

The positional behavior of habituated adult chimpanzees and baboons was observed for 784 hr in a year-long study. Comparisons between species were made to establish the distinctiveness of chimpanzee positional behavior and habitat use. Brachiation (sensu stricto, i.e., hand-over-hand suspensory locomotion) was observed in low frequencies among chimpanzees, and its significance for chimpanzee anatomy is judged slight. Although no significant differences were found between sympatric baboons and chimpanzees in the proportion of time spent in the terminal branches, or in the mean diameter of weight-bearing strata, chimpanzees exhibited evidence of a terminal branch adaptation in that they, unlike baboons, used postures among smaller supporting strata different from those used among larger supports. Among chimpanzees, unimanual arm-hanging was most common among the smallest strata and was associated with smaller mean and median support diameter than other postures. Unimanual arm-hanging was the only common behavior among chimpanzees that usually involved complete abduction of the humerus. A number of behaviors often subsumed under the label "quadrumanous climbing" were distinguished in this study. Compared to baboons and other cercopithecoids, chimpanzees did not show increased frequencies of large-stratum vertical climbing, and their vertical climbing did not involve significant humeral abduction. Arm-hanging (i.e., unimanual suspension) and vertical climbing distinguish chimpanzee positional behavior from that of monkeys.     

Facultative terrestrial hand postures in an orangutan (Pongo pygmaeus) and pongid evolution

An adult male orangutan at the Chicago Zoological Park utilizes various knuckle-walking hand postures in terrestrial bipedal-squatting and quadrupedal diagonal-sequence, diagonal-couplet gaits. A study was conducted in order to discern the circumstances surrounding the subject's terrestrial locomotor modes. It was found that various locomotor behaviors correlate with specific conditions of the substrate and the subject's motivation. Biomechanical properties of orangutan knuckle-walking are discussed in terms of their relevance for modelling hominoid phylogeny.     

Analysis of the shoulder in brachiating spider monkeys.

Adult spider monkeys (Ateles geoffroyi and A. paniscus) were conditioned to brachiate on a rope mill (an arboreal analogue of a treadmill). The postures and excursions of the shoulder girdle were studied by cineradiography. These data, together with conventional cinematographic and anatomical studies, permit reassessment of some characteristic structural and functional features of the shoulder in brachiators. During the propulsive phase, the shoulder joint moves caudad from fifth cervical to seventh cervical levels; at the same time, the joint moves dorsad (from a frontal plane midway between the first thoracic vertebra and the manubrium, to a frontal plane through the spinous processes) and slightly mediad. Spider monkeys position the scapula principally on the dorsum of the thorax, in contrast to quadrupedal primates which maintain a more lateral position (even in suspended postures). During brachiation, the scapula rotates a total of 35°; most of this rotation (20°) occurs in the non-propulsive phase when the free arm is being elevated to secure a new handhold. The sigmoidal shape, twisting of proximal relative to distal ends, and elongation of the clavicle in spider monkeys and other brachiators appear to be related to the specialized positioning of the shoulder girdle on the dorsum of the thorax. Shoulder and elbow movements contribute to the efficiency of the swing in terms of the dynamics of a pendulum.     

The behavioral ecology of sympatric African apes: implications for understanding fossil hominoid ecology

The behavioral ecology of the great apes is key evidence used in the reconstruction of the behavior of extinct ape and hominid taxa. Chimpanzees and gorillas have been studied in detail in the wild, and some studies of their behavioral ecology in sympatry have also been been carried out. Although the two ape species have divergent behavior and ecology in important respects, recent studies have shown that the interspecific differences are not as stark as previously thought and subsequently urge new consideration of how they share forest resources when sympatric. These new data require re-examination of assumptions about key aspects of chimpanzee-gorilla ecological divergence, such as diet, ranging and nesting patterns, and the mating system. Diet is a key component of the species adaptive complexes that facilitates avoidance of direct competition from the other. While the nutritional basis for chimpanzee food choice remains unclear and no doubt varies from site to site, this species is a ripe fruit specialist and ranges farther during periods of ripe fruit scarcity. Gorillas in the same habitat also feed on ripe fruit when widely available, but fall back onto fibrous plant foods during lean periods. The inclusion of animal protein in the diet of the chimpanzees and its absence in that of the gorillas also distinguish the species ecologically. It may also offer clues to aspects of ecological divergence among early members of the hominid phylogeny. The paper concludes by suggesting likely characteristics of sympatric associations of Pliocene hominids, based on field data from extant sympatric apes.     

Failure to demonstrate self-recognition in gorillas

Two zoo-reared gorillas were each given nearly 400 h of mirror exposure. Extensive mirror gazing and social behaviors were exhibited, the frequency of which decreased gradually over the study period. Neither animal demonstrated the transition from other-directed to self-directed behavior characteristic of both chimpanzees and orangutans, and no evidence of self-recognition was found using the Gallup marking paradigm. These negative findings, after extensive mirror exposure, suggest that the gorilla may be the only great ape which lacks the conceptual ability necessary for self-recognition.     

Beiträge zur Menschenaffenhaltung im Zoo Berlin nach 1945. 3. Mitteilung: Gorillas (Gorilla gorilla)

Since 1956 were Western Lowland Gorillas (Gorilla gorilla gorilla) kept in Berlin Zoo, counted in the period after 1945. The first offspring was born in 1964. Up to now 9 Gorillas were born in Berlin Zoo, of which 8 were raised, some of them artificial. The oldest Gorilla is “Fatou”, she is now in an age of 53.     

Mechanical implications of chimpanzee positional behavior.

Mechanical hypotheses concerning the function of chimpanzee anatomical specializations are examined in light of recent positional behavior data. Arm-hanging was the only common chimpanzee positional behavior that required full abduction of the humerus, and vertical climbing was the only distinctive chimpanzee positional behavior that required forceful retraction of the humerus and flexion of the elbow. Some elements of the chimpanzee anatomy, including an abductible humerus, a broad thorax, a cone-shaped torso, and a long, narrow scapula, are hypothesized to be a coadapted functional complex that reduces muscle action and structural fatigue during arm-hanging. Large muscles that retract the humerus (latissimus dorsi and probably sternocostal pectoralis major and posterior deltoid) and flex the elbow (biceps brachii, probably brachialis and brachioradialis) are argued to be adaptations to vertical climbing alone. A large ulnar excursion of the manus and long, curved metacarpals and phalanges are interpreted as adaptations to gripping vertical weight-bearing structures during vertical climbing and arm-hanging. A short torso, an iliac origin of the latissimus dorsi, and large muscles for arm-raising (caudal serratus, teres minor, cranial trapezius, and probably anterior deltoid and clavicular pectoralis major) are interpreted as adaptations to both climbing and unimanual suspension.     

Skeletal evidence of probable treponemal infection in free-ranging African apes

The prevalence and patterning of inflammatory lesions of the skeleton were investigated in samples of chimpanzees (Pan troglodytes troglodytes) and gorillas (Gorilla gorilla gorilla) curated at the Powell-Cotton Museum, Birchington, UK. One hundred and two chimpanzees (42 adults and 60 subadults) and 126 gorillas (50 adults and 76 subadults) comprise the samples. Twenty per cent of chimpanzees and 14% of gorillas were affected with a disseminated inflammatory skeletal condition caused by infection. The lesions appear to have originated as localized patches of new bone deposition on the surface of long bones and to have progressed to infection of the bone cortex and marrow. Although female prevalence of involvement exceeds that of males in both species, the differences are not statistically significant. The age distribution of affected animals indicates that the disease began in some animals as early as 2 yr of age. Given the skeletal and demographic prevalence and patterning of the lesions as well as the ecology and behavior of these animals, the most likely diagnosis of the condition is a yaws-like treponemal infection.