First description of the baubellum in the spectacled bear Tremarctos ornatus (Mammalia: Ursidae).

The baubellum (os clitoridis) is a bone found in the clitoris of many female eutherian mammals and is homologous to the baculum in males. In contrast to the baculum, the baubellum has received very little attention regarding its morphological or interspecific diversity, or on hypotheses for its function. The presence of the baubellum in bears (Ursidae) has only been established and mentioned in the literature for the Ursus genus, and not for the other genera of bears. Moreover, no scaled photographs are available for baubella of this clade, and the sizes reported vary between sources. We hereby present and describe the baubellum of a spectacled bear (Tremarctos ornatus), providing a detailed account of baubella in a basal ursid species. The baubellum of Tremarctos is slightly bowed dorsally, with two small prominences at the distal apex. The length of the Tremarctos baubellum in this study is comparable to that of Ursus americanus (American black bear). We infer the specific shape, with longitudinal ridges, of the baubellum in Tremarctos could indicate a discrete function during copulation or sexual arousal. However, future studies, especially regarding the associated soft tissues, will be required to confirm whether this is indeed the case. Our study expands the understanding of baubella within Ursidae, providing new data (including a three-dimensional model) that can be used to further explore the morphological diversity and function of this enigmatic extra-skeletal bone.

From quadrupedal to bipedal walking 'on the fly': the mechanics of dynamical mode transition in primates.

We investigated how baboons transition from quadrupedal to bipedal walking without any significant interruption in their forward movement (i.e. transition 'on the fly'). Building on basic mechanical principles (momentum only changes when external forces/moments act on the body), insights into possible strategies for such a dynamical mode transition are provided and applied first to the recorded planar kinematics of an example walking sequence (including several continuous quadrupedal, transition and subsequent bipedal steps). Body dynamics are calculated from the kinematics. The strategy used in this worked example boils down to: crouch the hind parts and sprint them underneath the rising body centre of mass. Forward accelerations are not in play. Key characteristics of this transition strategy were extracted: progression speed, hip height, step duration (frequency), foot positioning at touchdown with respect to the hip and the body centre of mass (BCoM), and congruity between the moments of the ground reaction force about the BCoM and the rate of change of the total angular moment. Statistical analyses across the full sample (15 transitions of 10 individuals) confirm this strategy is always used and is shared across individuals. Finally, the costs (in J kg-1 m-1) linked to on the fly transitions were estimated. The costs are approximately double those of both the preceding quadrupedal and subsequent bipedal walking. Given the short duration of the transition as such (<1 s), it is argued that the energetic costs to change walking posture on the fly are negligible when considered in the context of the locomotor repertoire.

The quadrupedal walking gait of the olive baboon, Papio anubis: an exploratory study integrating kinematics and EMG.

Primates exhibit unusual quadrupedal features (e.g. diagonal gaits, compliant walk) compared with other quadrupedal mammals. Their origin and diversification in arboreal habitats have certainly shaped the mechanics of their walking pattern to meet the functional requirements necessary for balance control in unstable and discontinuous environments. In turn, the requirements for mechanical stability probably conflict with mechanical energy exchange. In order to investigate these aspects, we conducted an integrative study on quadrupedal walking in the olive baboon (Papio anubis) at the Primatology station of the CNRS in France. Based on kinematics, we describe the centre of mass mechanics of the normal quadrupedal gait performed on the ground, as well as in different gait and substrate contexts. In addition, we studied the muscular activity of six hindlimb muscles using non-invasive surface probes. Our results show that baboons can rely on an inverted pendulum-like exchange of energy (57% on average, with a maximal observed value of 84%) when walking slowly (<0.9 m s-1) with a tight limb phase (∼55%) on the ground using diagonal sequence gaits. In this context, the muscular activity is similar to that of other quadrupedal mammals, thus reflecting the primary functions of the muscles for limb movement and support. In contrast, walking on a suspended branch generates kinematic and muscular adjustments to ensure better control and to maintain stability. Finally, walking using the lateral sequence gait increases muscular effort and reduces the potential for high recovery rates. The present exploratory study thus supports the assumption that primates are able to make use of an inverted pendulum mechanism on the ground using a diagonal walking gait, yet a different footfall pattern and substrate appear to influence muscular effort and efficiency.

Hip extensor mechanics and the evolution of walking and climbing capabilities in humans, apes, and fossil hominins.

The evolutionary emergence of humans' remarkably economical walking gait remains a focus of research and debate, but experimentally validated approaches linking locomotor capability to postcranial anatomy are limited. In this study, we integrated 3D morphometrics of hominoid pelvic shape with experimental measurements of hip kinematics and kinetics during walking and climbing, hamstring activity, and passive range of hip extension in humans, apes, and other primates to assess arboreal-terrestrial trade-offs in ischium morphology among living taxa. We show that hamstring-powered hip extension during habitual walking and climbing in living apes and humans is strongly predicted, and likely constrained, by the relative length and orientation of the ischium. Ape pelves permit greater extensor moments at the hip, enhancing climbing capability, but limit their range of hip extension, resulting in a crouched gait. Human pelves reduce hip extensor moments but permit a greater degree of hip extension, which greatly improves walking economy (i.e., distance traveled/energy consumed). Applying these results to fossil pelves suggests that early hominins differed from both humans and extant apes in having an economical walking gait without sacrificing climbing capability. Ardipithecus was capable of nearly human-like hip extension during bipedal walking, but retained the capacity for powerful, ape-like hip extension during vertical climbing. Hip extension capability was essentially human-like in Australopithecus afarensis and Australopithecus africanus, suggesting an economical walking gait but reduced mechanical advantage for powered hip extension during climbing.

Traditional high jump Gusimbuka Urukiramende: Could early 20th century African athletes beat Olympic champions?

During the first half of the 20th century, extraordinary high jumping performances of East-African athletes were observed. These athletes used a specific native jumping style called Gusimbuka Urukiramende. Eye-witnesses believed that these performances could have been world-records and that these athletes could have competed at the Olympics. However, these athletes never participated in international competitions and there is no other proof to support these performance claims. We have analysed historical photos and cine sequences of these jumps, documented the movement analysis of this technique, quantified performance and compared it to contemporaneous elite performances. Our analyses demonstrate that Gusimbuka Urukiramende athletes did not jump as high as the world record. Nevertheless, even though they used a suboptimal jump technique (because they had to lift their bodies higher to cross the bar) they could cross bar heights of 188 cm or 106% body height and as such their performance still was worthy of participation to the Olympics.

Habitat use and vestibular system's dimensions in lacertid lizards.

The vestibular system is crucial for movement control during locomotion. As the dimensions of the vestibular system determine the fluid dynamics of the endolymph and, as such, the system's function, we investigate the interaction between vestibular system size, head size and microhabitat use in lizards. We grouped 24 lacertid species in three microhabitat types, we acquired three-dimensional models of the bony vestibular systems using micro-computer tomography scanning, and we performed linear and surface measurements. All vestibular measurements scale with a negative allometry with head size, suggesting that smaller heads house disproportionally large ears. As the sensitivity of the vestibular system is positively related to size, a sufficiently large vestibular system in small-headed animals may meet the sensitivity demands during challenged locomotion. We also found that the microhabitat affects the locomotor dynamics: lizards inhabiting open microhabitats run at higher dimensionless speeds. On the other hand, no statistical relationship exists between dimensionless speed and the vestibular system dimensions. Hence, if the vestibular size would differ between microhabitats, this would be a direct effect (i.e. imposed, for instance, by requirements for manoeuvring, balance control, etc.), rather than depending on the lizards' intrinsic running speed. However, we found no effect of the microhabitat on the allometric relationship between head and vestibular system size. The finding that microhabitat is not reflected in the vestibular system size (hence sensitivity) of the lacertids in this study is possibly due to spatial constraints of the skull.

Compliant legs enable lizards to maintain high running speeds on complex terrains.

Substrate variations are likely to constrain animal performance in natural environments, as running over complex terrains challenges the dynamic stability of the body differently in each step. Yet, being able to negotiate complex terrains at top speed is a strong advantage for animals that have to deal with predators and evasive prey. Little is known on how animals negotiate such terrain variability at high speed. We investigated this in fast-running Acanthodactylus boskianus lizards, by measuring their 3D kinematics using four synchronised high-speed video cameras (325 Hz) on an adaptable racetrack. This racetrack was covered with four different substrates, representing increasing levels of terrain complexity. We found that the lizards deal with this complexity gradient by gradually adopting more erect parasagittal leg postures. Legs in a more-erect position are more compliant and are therefore highly adjustable on complex terrains. Additionally, the lizards stabilise their head, which facilitates vestibular and visual perception. Together, compliant legs and head stabilisation enable the lizards to minimise movements of the body centre of mass, even when running on highly irregular terrains. This suggests that the head and the centre of mass are the priority targets for running on uneven terrains. As a result, running performance (mean forward speed) decreases only slightly, and only on the most challenging substrate under investigation.

The gibbon's Achilles tendon revisited: consequences for the evolution of the great apes?

The well-developed Achilles tendon in humans is generally interpreted as an adaptation for mechanical energy storage and reuse during cyclic locomotion. All other extant great apes have a short tendon and long-fibred triceps surae, which is thought to be beneficial for locomotion in a complex arboreal habitat as this morphology enables a large range of motion. Surprisingly, highly arboreal gibbons show a more human-like triceps surae with a long Achilles tendon. Evidence for a spring-like function similar to humans is not conclusive. We revisit and integrate our anatomical and biomechanical data to calculate the energy that can be recovered from the recoiling Achilles tendon during ankle plantar flexion in bipedal gibbons. Only 7.5% of the required external positive work in a stride can come from tendon recoil, yet it is delivered at an instant when the whole-body energy level drops. Consequently, an additional similar amount of mechanical energy must simultaneously dissipate elsewhere in the system. Altogether, this challenges the concept of an energy-saving function in the gibbon's Achilles tendon. Cercopithecids, sister group of the apes, also have a human-like triceps surae. Therefore, a well-developed Achilles tendon, present in the last common 'Cercopithecoidea-Hominoidea' ancestor, seems plausible. If so, the gibbon's anatomy represents an evolutionary relict (no harm-no benefit), and the large Achilles tendon is not the premised key adaptation in humans (although the spring-like function may have further improved during evolution). Moreover, the triceps surae anatomy of extant non-human great apes must be a convergence, related to muscle control and range of motion. This perspective accords with the suggestions put forward in the literature that the last common hominoid ancestor was not necessarily great ape-like, but might have been more similar to the small-bodied catarrhines.

Segmental morphometrics of bonobos (Pan paniscus): are they really different from chimpanzees (Pan troglodytes)?

The inertial properties of body segments reflect performance and locomotor habits in primates. While Pan paniscus is generally described as more gracile, lighter in body mass, and as having relatively longer and heavier hindlimbs than Pan troglodytes, both species exhibit very similar patterns of (quadrupedal and bipedal) kinematics, but show slightly different locomotor repertoires. We used a geometric model to estimate the inertial properties for all body segments (i.e. head, trunk, upper and lower arms, hand, thigh, shank and foot) using external length and diameter measurements of 12 anaesthetized bonobos (eight adults and four immatures). We also calculated whole limb inertial properties. When we compared absolute and relative segment morphometric and inertial variables between bonobos and chimpanzees, we found that adult bonobos are significantly lighter than adult chimpanzees. The bonobo is also shorter in head length, upper and lower arm lengths, and foot length, and is generally lighter in most absolute segment mass values (except head and hand). In contrast, the bonobo has a longer trunk. When scaled relative to body mass, most differences disappear between the two species. Only the longer trunk and the shorter head of the bonobo remain apparent, as well as the lighter thigh compared with the chimpanzee. We found similar values of natural pendular periods of the limbs in both species, despite differences in absolute limb lengths, masses, mass centres (for the hindlimb) and moments of inertia. While our data contradict the commonly accepted view that bonobos have relatively longer and heavier hindlimbs than chimpanzees, they are consistent with the observed similarities in the quadrupedal and bipedal kinematics between these species. The morphological differences between both species are more subtle than those previously described from postcranial osteological materials.

Aquatic-terrestrial transitions of feeding systems in vertebrates: a mechanical perspective.

Transitions to terrestrial environments confront ancestrally aquatic animals with several mechanical and physiological problems owing to the different physical properties of water and air. As aquatic feeders generally make use of flows of water relative to the head to capture, transport and swallow food, it follows that morphological and behavioral changes were inevitably needed for the aquatic animals to successfully perform these functions on land. Here, we summarize the mechanical requirements of successful aquatic-to-terrestrial transitions in food capture, transport and swallowing by vertebrates and review how different taxa managed to fulfill these requirements. Amphibious ray-finned fishes show a variety of strategies to stably lift the anterior trunk, as well as to grab ground-based food with their jaws. However, they still need to return to the water for the intra-oral transport and swallowing process. Using the same mechanical perspective, the potential capabilities of some of the earliest tetrapods to perform terrestrial feeding are evaluated. Within tetrapods, the appearance of a mobile neck and a muscular and movable tongue can safely be regarded as key factors in the colonization of land away from amphibious habitats. Comparative studies on taxa including salamanders, which change from aquatic feeders as larvae to terrestrial feeders as adults, illustrate remodeling patterns in the hyobranchial system that can be linked to its drastic change in function during feeding. Yet, the precise evolutionary history in form and function of the hyolingual system leading to the origin(s) of a muscular and adhesive tongue remains unknown.

Segmental morphometrics of the olive baboon (Papio anubis): a longitudinal study from birth to adulthood.

The linear dimensions and inertial characteristics of the body are important in locomotion and they change considerably during the ontogeny of animals, including humans. This longitudinal and ontogenetic study has produced the largest dataset to date of segmental morphometrics in a Catarrhini species, the olive baboon. The objectives of the study were to quantify the changes in body linear and inertial dimensions and to explore their (theoretical) mechanical significance for locomotion. We took full-body measurements of captive individuals at regular intervals. Altogether, 14 females and 16 males were followed over a 7-year period, i.e. from infancy to adulthood. Our results show that individual patterns of growth are very consistent and follow the general growth pattern previously described in olive baboons. Furthermore, we obtained similar growth curve structures for segment lengths and masses, although the respective time scales were slightly different. The most significant changes in body morphometrics occurred during the first 2 years of life and concerned the distal parts of the body. Females and males were similar in size and shape at birth. The rate and duration of growth produced substantial size-related differences throughout ontogeny, while body shapes remained very similar between the sexes. We also observed significant age-related variations in limb composition, with a proximal shift of the centre of mass within the limbs, mainly due to changes in mass distribution and in the length of distal segments. Finally, we observed what we hypothesize to be 'early biomechanical optimization' of the limbs for quadrupedal walking. This is due to a high degree of convergence between the limbs' natural pendular periods in infants, which may facilitate the onset of quadrupedal walking. Furthermore, the mechanical significance of the morphological changes observed in growing baboons may be related to changing functional demands with the onset of autonomous (quadrupedal) locomotion. From a wider perspective, these data provide unique insights into questions surrounding both the processes of locomotor development in primates and how these processes might evolve.

The effect of craniokinesis on the middle ear of domestic chickens (Gallus gallus domesticus).

The avian middle ear differs from that of mammalians and contains a tympanic membrane, one ossicle (bony columella and cartilaginous extra-columella), some ligaments and one muscle. The rim of the eardrum (closing the middle ear cavity) is connected to the neurocranium and, by means of a broad ligament, to the otic process of the quadrate. Due to the limited number of components in the avian middle ear, the possibilities of attenuating the conduction of sound seem to be limited to activity of the stapedius muscle. We investigate to what extent craniokinesis may impact the components of the middle ear because of the connection of the eardrum to the movable quadrate. The quadrate is a part of the beak suspension and plays an important role in craniokinesis. Micro-computed tomography was used to visualize morphology and the effect of craniokinesis on the middle ear in the domestic chicken (Gallus gallus domesticus). Both hens and roosters are considered because of their difference in vocalization capacity. It is hypothesized that effects, if present, of craniokinesis on the middle ear will be greater in roosters because of their louder vocalization. Maximal lower jaw depression was comparable for hens and roosters (respectively 34.1 ± 2.6° and 32.7 ± 2.5°). There is no overlap in ranges of maximal upper jaw elevation between the sexes (respectively 12.7 ± 2.5° and 18.5 ± 3.8°). Frontal rotation about the transversal quadrato-squamosal, and inward rotation about the squamosal-mandibular axes of the quadrate were both considered to be greater in roosters (respectively 15.4 ± 2.8° and 11.1 ± 2.5°). These quadrate rotations did not affect the columellar position or orientation. In hens, an influence of the quadrate movements on the shape of the eardrum could not be detected either; however, craniokinesis caused slight stretching of the eardrum towards the caudal rim of the otic process of the quadrate. In roosters, an inward displacement of the conical tip of the tympanic membrane of 0.378 ± 0.21 mm, as a result of craniokinesis, was observed. This is linked to a flattening and slackening of the eardrum. These changes most likely go along with a deformation of the extra-columella. Generally, in birds, larger beak opening is related to the intensity of vocalization. The coupling between larger maximal upper jaw lifting in roosters and the slackening of the eardrum suggest the presence of a passive sound attenuation mechanism during self-vocalization.

The origin of bipedality as the result of a developmental by-product: The case study of the olive baboon (Papio anubis).

In this paper, we point to the importance of considering infancy in the emergence of new locomotor modes during evolution, and particularly when considering bipedal walking. Indeed, because infant primates commonly exhibit a more diverse posturo-locomotor repertoire than adults, the developmental processes of locomotion represent an important source of variation upon which natural selection may act. We have had the opportunity to follow the development of locomotion in captive individuals of a committed quadrupedal primate, the olive baboon (Papio anubis). We observed six infants at two different stages of their development. In total, we were able to analyze the temporal parameters of 65 bipedal steps, as well as their behavioral components. Our results show that while the basic temporal aspects of the bipedal walking gait (i.e., duty factor, dimensionless frequency, and hind lag) do not change during development, the baboon is able to significantly improve the coordination pattern between hind limbs. This probably influences the bout duration of spontaneous bipedal walking. During the same developmental stage, the interlimb coordination in quadrupedal walking is improved and the proportion of quadrupedal behaviors increases significantly. Therefore, the quadrupedal pattern of primates does not impede the developmental acquisition of bipedal behaviors. This may suggest that the same basic mechanism is responsible for controlling bipedal and quadrupedal locomotion, i.e., that in non-human primates, the neural networks for quadrupedal locomotion are also employed to perform (occasional) bipedal walking. In this context, a secondary locomotor mode (e.g., bipedalism) experienced during infancy as a by-product of locomotor development may lead to evolutionary novelties when under appropriate selective pressures.

How innate is locomotion in precocial animals? A study on the early development of spatio-temporal gait variables and gait symmetry in piglets.

Locomotion is one of the most important ecological functions in animals. Precocial animals, such as pigs, are capable of independent locomotion shortly after birth. This raises the question whether coordinated movement patterns and the underlying muscular control in these animals is fully innate or whether there still exists a rapid maturation. We addressed this question by studying gait development in neonatal pigs through the analysis of spatio-temporal gait characteristics during locomotion at self-selected speed. To this end, we made video recordings of piglets walking along a corridor at several time points (from 0 h to 96 h). After digitization of the footfalls, we analysed self-selected speed and spatio-temporal characteristics (e.g. stride and step lengths, stride frequency and duty factor) to study dynamic similarity, intralimb coordination and interlimb coordination. To assess the variability of the gait pattern, left-right asymmetry was studied. To distinguish neuromotor maturation from effects caused by growth, both absolute and normalized data (according to the dynamic similarity concept) were included in the analysis. All normalized spatio-temporal variables reached stable values within 4 h of birth, with most of them showing little change after the age of 2 h. Most asymmetry indices showed stable values, hovering around 10%, within 8 h of birth. These results indicate that coordinated movement patterns are not entirely innate, but that a rapid neuromotor maturation, potentially also the result of the rearrangement or recombination of existing motor modules, takes place in these precocial animals.

Musculoskeletal architecture of the prey capture apparatus in salamandrid newts with multiphasic lifestyle: does anatomy change during the seasonal habitat switches?

Some newt species change seasonally between an aquatic and a terrestrial life as adults, and are therefore repeatedly faced with different physical circumstances that affect a wide range of functions of the organism. For example, it has been observed that seasonally habitat-changing newts display notable changes in skin texture and tail fin anatomy, allowing one to distinguish an aquatic and a terrestrial morphotype. One of the main functional challenges is the switch between efficient aquatic and terrestrial prey capture modes. Recent studies have shown that newts adapt quickly by showing a high degree of behavioral flexibility, using suction feeding in their aquatic stage and tongue prehension in their terrestrial stage. As suction feeding and tongue prehension place different functional demands on the prey capture apparatus, this behavioral flexibility may clearly benefit from an associated morphological plasticity. In this study, we provide a detailed morphological analysis of the musculoskeletal system of the prey capture apparatus in the two multiphasic newt species Ichthyosaura alpestris and Lissotriton vulgaris by using histological sections and micro-computed tomography. We then test for quantitative changes of the hyobranchial musculoskeletal system between aquatic and terrestrial morphotypes, The descriptive morphology of the cranio-cervical musculoskeletal system provides new insights on form and function of the prey capture apparatus in newts, and the quantitative approach shows hypertrophy of the hyolingual musculoskeletal system in the terrestrial morphotype of L. vulgaris but hypertrophy in the aquatic morphotype of I. alpestris. It was therefore concluded that the seasonal habitat shifts are accompanied by a species-dependent muscular plasticity of which the potential effect on multiphasic feeding performance in newts remains unclear.

Jaw morphology and fighting forces in stag beetles.

The jaws of different species of stag beetles show a large variety of shapes and sizes. The male jaws are used as weapons in fights, and they may exert a very forceful bite in some species. We investigated in 16 species whether and how the forcefulness of their bite is reflected in their jaw morphology. We found a large range of maximal muscle forces (1.8-33 N; factor of 18). Species investing in large bite muscles also have disproportionately large jaw volumes. They use this additional jaw volume to elongate their jaws, increasing their chances of winning in battles. The fact that this also decreases the mechanical advantage is largely compensated for by elongated in-levers. As a result, high muscle forces are correlated with elevated bite forces (0.27-7.6 N; factor of 28). Despite the large difference in the forcefulness of their bite, all investigated species experience similar Von Mises stresses in their jaws while biting (29-114 MPa; factor of 4.0; calculated with finite element simulations). Hence, stag beetles have successfully adapted their jaw anatomy according to their bite force in fights.

Kinematics of mouthbrooding in Oreochromis niloticus (Cichlidae).

Many species from several different families of fishes perform mouthbrooding, where one of the sexes protects and ventilates the eggs inside the mouth cavity. This ventilation behaviour differs from gill ventilation outside the brooding period, as the normal, small-amplitude suction-pump respiration cycles are alternated with actions including near-simultaneous closed-mouth protrusions and high-amplitude depressions of the hyoid. The latter is called churning, referring to its hypothetical function in moving around and repositioning the eggs by a presumed hydrodynamic effect of the marked shifts in volume along the mouth cavity. We tested the hypothesis that churning causes the eggs located posteriorly in the mouth cavity to move anteriorly away from the gill entrance. This would prevent or clear accumulations of brood at the branchial basket, which would otherwise hinder breathing by the parent. Dual-view videos of female Nile tilapias (Oreochromis niloticus) during mouthbrooding showed that churning involves a posterior-to-anterior wave of expansion and compression of the head volume. Flow visualisation with polyethylene microspheres revealed a significant inflow of water entering the gill slits at the zone above the pectoral fin base, followed by a predominantly ventral outflow passing the ventrolaterally flapping branchiostegal membranes. X-ray videos indicated that particularly the brood located close to the gills is moved anteriorly during churning. These data suggest that, in addition to mixing of the brood to aid its oxygenation, an important function of the anterior flow through the gills and buccal cavity during churning is to prevent clogging of the eggs near the gills.

Bipedality from locomotor autonomy to adulthood in captive olive baboon (Papio anubis): Cross-sectional follow-up and first insight into the impact of body mass distribution.

OBJECTIVE: Despite that the biomechanics of standing and walking bipedally has been extensively studied in nonhuman primates, the morphological features that may constrain, or facilitate, the control of balance and thus of the spontaneous occurrence of bipedal behavior are poorly known. We aim to test the relationship between body mass distribution and bipedal behavior using a nonhuman primate species, the olive baboon, Papio anubis, raised in captivity. MATERIALS AND METHODS: We collected quantitative data on the frequency and duration of bipedalism together with morphometrics on a sample of 22 individuals. We used ontogenetic changes as a natural experiment that provides insights into the impact of morphology. Specifically we focus on 1) quantifying how body mass distribution changes from infancy to adulthood in baboons; and 2) whether the different patterns of mass distribution influence the behavioral variables, i.e., a) the frequency and b) the duration of bouts of bipedal behavior realized in different activity contexts. RESULTS: With regard to assisted bipedal behaviors, the duration and frequency of bouts of standing, contrary to walking, are significantly related to age. With regard to unassisted bipedal behaviors, no correlation to age is observed; the bout duration of walking is strongly correlated to body mass and mass distribution, contrary to the frequency of walking as well as the bout duration and frequency of bipedal standing. DISCUSSION: Our results suggest a close relationship between the pattern of mass distribution and the mechanism of balance control in the spontaneous bipedal walking of baboons. The mechanical effects of the pattern of mass distribution on the ability to perform bipedally in extant nonhuman primates are discussed in the context of the evolution toward habitual bipedalism.

Effect of body mass distribution on the ontogeny of positional behaviors in non-human primates: Longitudinal follow-up of infant captive olive baboons (Papio anubis).

The diversity of primates' positional capabilities is unique among mammals. Indeed, they exhibit a daily repertoire composed of various locomotor and postural modes that may be linked to their particular morphological pattern. Because ontogeny undergoes parallel behavioral and morphological modifications, it may be useful to investigate the biomechanical consequences of the changing body shape. We, therefore, collected accurate quantitative and longitudinal data on positional behaviors, body mass distribution patterns, activities, and environment on a sample of six infant olive baboons, Papio anubis. These baboons are kept at the Primatology Station of the CNRS, France, where they live within the same social group. Individual behaviors were quantified using the focal sampling method. The body mass distribution was estimated according to a geometric model based on direct external measurements. Multivariate analysis enabled us to analyze the interactions between the data. Our results show that body mass distribution changes together with the ontogenetic changes in positional behaviors. At an early age, individuals have distally heavy segment masses in the limbs and an important fraction of the behavioral repertoire involves efficient grasping abilities. At the end of infancy, the same individuals have relatively more mass in proximal segments of the limbs and the proportion of quadrupedal walking is significantly higher while other climbing and suspensory behaviors decreased substantially. The present study experimentally confirms the association between body mass distribution and the positional repertoire of primates. These relationships, when interpreted in the context of basic biomechanical concepts, may improve our understanding of primate locomotion. We discuss further the implications of these functional relationships when modeling the evolutionary pathway of primates. Am. J. Primatol. 78:1201-1221, 2016. © 2016 Wiley Periodicals, Inc.

Gait characteristics and spatio-temporal variables of climbing in bonobos (Pan paniscus).

Although much is known about the terrestrial locomotion of great apes, their arboreal locomotion has been studied less extensively. This study investigates arboreal locomotion in bonobos (Pan paniscus), focusing on the gait characteristics and spatio-temporal variables associated with locomotion on a pole. These features are compared across different substrate inclinations (0°, 30°, 45°, 60°, and 90°), and horizontal quadrupedal walking is compared between an arboreal and a terrestrial substrate. Our results show greater variation in footfall patterns with increasing incline, resulting in more lateral gait sequences. During climbing on arboreal inclines, smaller steps and strides but higher stride frequencies and duty factors are found compared to horizontal arboreal walking. This may facilitate better balance control and dynamic stability on the arboreal substrate. We found no gradual change in spatio-temporal variables with increasing incline; instead, the results for all inclines were clustered together. Bonobos take larger strides at lower stride frequencies and lower duty factors on a horizontal arboreal substrate than on a flat terrestrial substrate. We suggest that these changes are the result of the better grip of the grasping feet on an arboreal substrate. Speed modulation of the spatio-temporal variables is similar across substrate inclinations and between substrate types, suggesting a comparable underlying motor control. Finally, we contrast these variables of arboreal inclined climbing with those of terrestrial bipedal locomotion, and briefly discuss the results with respect to the origin of habitual bipedalism. Am. J. Primatol. 78:1165-1177, 2016. © 2016 Wiley Periodicals, Inc.