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A key characteristic of primate above-branch arboreal locomotion is hindlimb-biased weight support, subverting the typical mammalian condition in which the majority of the body weight is supported by the forelimb. This shift is thought to reflect an adaptation toward the arboreal niches exploited by early primates. However, above-branch quadrupedalism represents only one locomotor mode employed by primates in arboreal contexts. Inverted quadrupedal gaits, in which primates are suspended beneath branches by their hands and feet, have been documented in more than 50 primate taxa. This gait is characterized by a return to forelimb-biased weight distributions and a transition from peak vertical forces being greatest in the hindlimb to being greatest in the forelimb, which may occur to protect the hindlimb from high magnitudes of tensile loading when inverted. In this study, we compare kinetic and kinematic data during upright and inverted quadrupedalism in Lemur catta, Varecia variegata, Cebus capucinus, and Saimiri sciureus. These data are referenced against a classical inverted quadrupedal model: the two-toed sloth (Choloepus didactylus). Our findings show that inverted quadrupedalism in primates is differentiated from above-branch quadrupedalism by increases in forelimb weight support, forelimb contact times, and both forelimb and hindlimb joint excursions. Previously postulated biomechanical models outlining mechanisms relating to the control of weight support during upright walking do not translate well to inverted quadrupedal walking. We suggest that inverted primates may simply be adopting basal neuromuscular gait characteristics and applying them facultatively to this infrequent locomotor behavior., (© 2022 Wiley Periodicals LLC.)

Plesiadapiforms, like other Paleogene mammals, are known mostly from fossil teeth and jaw fragments. The several families of plesiadapiforms known from partial skeletons have all been reconstructed as arborealists, but differences in postcranial morphology among these taxa indicate a diversity of positional behaviors. Here we provide the first detailed descriptions and comparisons of a dentally associated partial skeleton (NMMNH P-54500) and of the most complete dentary with anterior teeth (NMMNH P-71598) pertaining to Torrejonia wilsoni, from the early Paleocene (late Torrejonian To3 interval zone) of the Nacimiento Formation, San Juan Basin, New Mexico, USA. NMMNH P-54500 is the oldest known partial skeleton of a plesiadapiform and the only known postcrania for the Palaechthonidae. This skeleton includes craniodental fragments with all permanent teeth fully erupted, and partial forelimbs and hind limbs with some epiphyses unfused, indicating that this individual was a nearly fully-grown subadult. Analysis of the forelimb suggests mobile shoulder and elbow joints, a habitually flexed forearm, and capacity for manual grasping. The hip joint allowed abduction and lateral rotation of the thigh and provides evidence for frequent orthograde postures on large diameter supports. Other aspects of the hind limb suggest a habitually flexed thigh and knee with no evidence for specialized leaping, and mobile ankle joints capable of high degrees of inversion and eversion. Although it is likely that some variability exists within the group, analysis of this skeleton suggests that palaechthonids are most like paromomyids among plesiadapiforms, but retain more plesiomorphic postcranial features than has been documented for the Paromomyidae. These observations are congruent with craniodental evidence supporting palaechthonids and paromomyids as closely related within the Paromomyoidea. The skeleton of T. wilsoni also demonstrates that many regions of the postcranium were already well adapted for arboreality within the first few million years of the diversification of placental mammals following the Cretaceous-Paleogene extinction event., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The link between laterality in humans and other primates is still hotly debated. Hylobatids have been rather neglected in this research area, yet they can provide important insights because: (1) they share with humans a complex vocal repertoire, which in humans is thought to be associated with brain hemispheric specialization and lateralized behaviors; (2) their adaptation to arboreality has produced unique postural constraints; (3) the little that is known about laterality in gibbons is contradictory (captive studies have provided conflicting results, while a field study on siamangs reported a population-level left-hand preference). To clarify this, we investigated hand preference in captive hylobatids [n = 42; 22 siamangs (Symphalangus syndactylus) and 20 gibbons (Hylobates sp., Nomascus leucogenys)] in nine Japanese facilities. We had a large sample size, controlled for possible confounds (posture, enclosure limitations) and used a well-established testing protocol (tube task). Handedness indices calculated from raw frequencies and bouts were highly correlated and showed a significant left-hand skew, which is consistent with data from wild siamangs. Major differences between captive and wild siamangs were a larger number of ambiguously handed individuals, and no significant age-related variation in captivity. The use of the index finger elicited a much more strongly lateralized response than the thumb. These results confirmed a left-hand preference in siamangs, but were equivocal in other hylobatids, and suggest selective pressures that may have acted on the highly arboreal hylobatids to favor handedness. Our study also indicates factors that might explain the discrepancy in the literature between handedness studies on captive and wild primate populations.

Objectives: An accident during arboreal locomotion can lead to risky falls, but it remains unclear that the extent to which primates, as adept arborealists, change their locomotion in response to the perceived risk of moving on high supports in the tree canopy. By using more stable forms of locomotion on higher substrates, primates might avoid potentially fatal consequences. Materials and Methods: Using high‐speed cameras, we recorded the quadrupedal locomotion of four wild lemur species—Eulemur rubriventer, Eulemur rufifrons, Hapalemur aureus, and Lemur catta (N = 113 total strides). We quantified the height, diameter, and angular orientation of locomotor supports using remote sensors and tested the influence of support parameters on gait kinematics, specifically predicting that in response to increasing substrate height, lemurs would decrease speed and stride frequency, but increase stride length and the mean number of supporting limbs. Results: Lemurs did not adjust stride frequency on substrates of varying height. Adjustments to speed, stride length, and the mean number of supporting limbs in response to varying height often ran counter to predictions. Only E. rubriventer decreased speed and increased the mean number of supporting limbs on higher substrates. Discussion: Results suggest that quadrupedal walking is a relatively safe form of locomotion for lemurs, requiring subtle changes in gait to increase stability on higher—that is, potentially riskier—substrates. Continued investigation of the impact of height on locomotion will be important to determine how animals assess risk in their environment and how they choose to use this information to move more safely. Research Highlights: Substrate height can increase the risk of injury after a fall.Lemurs make subtle and variable adjustments to gait in response to substrate height.Substrate height will be important to include in future studies of wild primate locomotion. [ABSTRACT FROM AUTHOR]

Objectives: Despite qualitative observations of wild primates pumping branches before leaping across gaps in the canopy, most studies have suggested that support compliance increases the energetic cost of arboreal leaping, thus limiting leaping performance. In this study, we quantified branch pumping behavior and tree swaying in wild primates to test the hypothesis that these behaviors improve leaping performance. Materials and Methods: We recorded wild colobine monkeys crossing gaps in the canopy and quantitatively tracked the kinematics of both the monkey and the compliant support during behavioral sequences. We also empirically measured the compliance of a sample of locomotor supports in the monkeys' natural habitat, allowing us to quantify the resonant properties of substrates used during leaping. Results: Analyses of three recordings show that adult red colobus monkeys (Piliocolobus tephrosceles) use branch compliance to their advantage by actively pumping branches before leaping, augmenting their vertical velocity at take‐off. Quantitative modeling of branch resonance periods, based on empirical measurements of support compliance, suggests that monkeys specifically employed branch pumping on relatively thin branches with protracted periods of oscillation. Finally, an additional four recordings show that both red colobus and black and white colobus monkeys (Colobus guereza) utilize tree swaying to cross large gaps, augmenting horizontal velocity at take‐off. Discussion: This deliberate branch manipulation to produce a mechanical effect for stronger propulsion is consistent with the framework of instrumental problem‐solving. To our knowledge, this is the first study of wild primates which quantitatively shows how compliant branches can be used advantageously to augment locomotor performance. [ABSTRACT FROM AUTHOR]

Objectives: The primate foot has been extensively investigated because of its role in weight‐bearing; however, the calcaneus has been relatively understudied. Here we examine entire gorilla calcaneal external shape to understand its relationship with locomotor behavior. Materials and methods: Calcanei of Gorilla gorilla gorilla (n = 43), Gorilla beringei graueri (n = 20), and Gorilla beringei beringei (n = 15) were surface or micro‐CT scanned. External shape was analyzed through a three‐dimensional geometric morphometric sliding semilandmark analysis. Semilandmarks were slid relative to an updated Procrustes average in order to minimize the bending energy of the thin plate spline interpolation function. Shape variation was summarized using principal components analysis of shape coordinates. Procrustes distances between taxa averages were calculated and resampling statistics run to test pairwise differences. Linear measures were collected and regressed against estimated body mass. Results: All three taxa exhibit statistically different morphologies (p <.001 for pairwise comparisons). G. g. gorilla demonstrates an anteroposteriorly elongated calcaneus with a deeper cuboid pivot region and mediolaterally flatter posterior talar facet. G. b. beringei possesses the flattest cuboid and most medially‐angled posterior talar facets. G. b. graueri demonstrates intermediate articular facet morphology, a medially‐angled tuberosity, and an elongated peroneal trochlea. Discussion: Articular facet differences separate gorillas along a locomotor gradient. G. g. gorilla is adapted for arboreality with greater joint mobility, while G. b. beringei is adapted for more stereotypical loads associated with terrestriality. G. b. graueri's unique posterolateral morphology may be due to a secondary transition to greater arboreality from a more terrestrial ancestor. [ABSTRACT FROM AUTHOR]

Locomotor diversity has meant many different things depending on the subject area or investigator. While no concrete definition of locomotor diversity is currently available, this has not stopped researchers from making a number of assertions about the underlying mechanisms that determine whether a species will have high or low locomotor diversity. Some of these claims include that: (1) arboreal primates demonstrate higher locomotor diversity than terrestrial species; (2) anatomically generalized and small‐bodied primates demonstrate higher locomotor diversity than anatomically specialized and large‐bodied taxa; and (3) primates demonstrate higher locomotor diversity compared to non‐primate mammals. None of these claims have been tested in any sort of comparative framework. Using previously published locomotor repertoire data from 110 mammalian species, this study co‐opted the Shannon–Wiener diversity index to calculate a singular measure of locomotor diversity. Phylogenetic analyses of these locomotor diversity indices reveal that within primates, small‐bodied species demonstrate greater locomotor diversity than large‐bodied taxa. However, this effect becomes non‐significant when accounting for differences in substrate‐use (i.e. arboreal vs. terrestrial). Anatomical specialization has no effect on locomotor diversity in primates. Furthermore, primates do not inherently have greater locomotor diversity than other mammalian taxa. Findings from this study suggest that movement on arboreal substrates requires all mammals, regardless of taxonomic affiliation, to demonstrate high locomotor diversity. These data further highlight the challenges faced by arboreal animals and raise the possibility that being able to switch fluidly and frequently between many different locomotor modes may be advantageous for animals moving in an arboreal milieu. Locomotor diversity has meant many different things depending on the subject area or investigator, but there is no concrete definition of locomotor diversity currently available. Using previously published locomotor repertoire data from 110 mammalian species, this study co‐opted the Shannon–Wiener diversity index to calculate a singular measure of locomotor diversity. Phylogenetic analyses of these locomotor diversity indices reveal that within primates, small‐bodied species demonstrate greater locomotor diversity than large‐bodied taxa. Furthermore, primates do not inherently have greater locomotor diversity than other mammalian taxa. Findings from this study suggest that movement on arboreal substrates requires all mammals, regardless of taxonomic affiliation, to demonstrate high locomotor diversity. These data further highlight the challenges faced by arboreal animals and raise the possibility that being able to switch fluidly and frequently between many different locomotor modes may be advantageous for animals moving in an arboreal milieu. [ABSTRACT FROM AUTHOR]

Nearly all primates are ecologically dependent on trees, but they are nonetheless found in an enormous range of habitats, from highly xeric environments to dense rainforest. Most primates have a relatively 'generalised' skeleton, enabling locomotor flexibility and facilitating other crucial functions, such as manual foraging and grooming. This paper explores the associations between habitat, locomotion and morphology in the forelimbs of cercopithecids (Old World monkeys), contextualising their skeletal ecomorphological patterns with those of other mammals, and complementing functional morphological analyses with phylogenetic comparative techniques. The ecomorphological signals present in the generalised primate postcranium, and how an ancestral arboreal 'bauplan' might be modified to incorporate terrestriality or exploit distinct arboreal substrates, are investigated. Analysis of ecomorphological variation in guenons indicates that terrestrial Chlorocebus species retain core elements of a general guenon form, with modifications for terrestriality that vary by species. Adaptation to different modes of arboreality has also occurred in Cercopithecus. The considerable morphological similarity in the guenons sampled emphasises the importance of generality in the primate postcranium - much forelimb variation appears to have emerged stochastically, with a smaller number of traits having a strong functional signal. Analysis of a broader sample of cercopithecids and comparison with felids, suids and bovids indicates that although the cercopithecid humerus has functional morphological signals that enable specimens to be assigned with a reasonable degree of certainty to habitat groups, there is considerable overlap in the specimens assigned to each habitat group. This probably reflects ecological dependence on trees, even in predominantly terrestrial species, as well as the multiple functions of the forelimb and, in some cases, wide geographic distributions that promote intraspecific variation. The use of phylogenetic correction reduced the discriminatory power of the models, indicating that, like allometry, phylogeny contains important ecomorphological information, and should not necessarily be factored out of analyses. [ABSTRACT FROM AUTHOR]

Abstract: The genus Mesopithecus is well represented in the late Miocene of Greece by several recognized species. The present paper investigates functional aspects of the humeri of Mesopithecus delsoni/pentelicus, M. pentelicus and M. aff. pentelicus of several Turolian sites from central and northern Greece, using multivariate approaches. For these purposes, we selected significant humeral functional features, which were represented by 23 linear dimensions and three angles on 14 fossil humeri and 104 humeri from 10 genera and 22 species of extant African and Asian Colobines. All size-adjusted measurements were examined through a principal components analysis, followed by a discriminant function analysis, and a canonical variates analysis. All analyses revealed that the selected characters were able to discriminate between extant colobine genera. Functional groups, such as arboreal walking/climbing, arboreal walking/suspensory and semi-terrestrial walking, were set apart from a central cluster formed by the arboreal walking and arboreal walking/terrestrial groups. This cluster also grouped the three studied Mesopithecus species, which were mainly classified as arboreal walkers with significant terrestrial activities. These observations match with paleoenvironmental reconstructions and the suggested opportunistic feeding habits. Moreover, the overall arboreal/terrestrial locomotor tendencies of these fossil forms are discussed in relation to their earlier migration from Africa and later dispersal to eastern and southern Asia. [Copyright &y& Elsevier]

Abstract: Locomotor features shared by arboreal marsupials and primates are frequently cited as a functional complex that evolved in the context of a “fine branch niche.” Adaptation to a fine branch niche cannot be understood without considering that small and large arboreal mammals may differ in their biomechanical response to a given branch size. We tested the effects of substrate diameter and orientation on quadrupedal kinematics in a small arboreal marsupial (the sugar glider, Petaurus breviceps). P. breviceps individuals were filmed moving across a flat horizontal surface and on horizontal, inclining and declining poles of diameter 2.5, 1.0, and 0.5cm. Gait frequencies, limb phases, speeds and duty factors were compared across substrate conditions. P. breviceps had a clear preference for lateral sequence/diagonal couplets gaits, regardless of substrate type, diameter or orientation. Limb phase was significantly influenced by substrate type (higher limb phases on poles vs. the flat surface) and by orientation (higher limb phases on inclined vs. horizontal poles), but was not influenced by pole diameter. Speed was lowest on declines, and duty factors (at a given speed) were highest on the flat board, smallest pole, and on declines. P. breviceps exhibited some parallels, but also some departures from the characteristic patterns of other arboreal marsupials and primates. Notably, limb phase values, on average, remained lower in P. breviceps than those recorded for primates or other arboreal marsupials. We suggest that arboreal mammals of different body sizes may use dissimilar, but apparently equally successful strategies for navigating a “fine branch niche.” [Copyright &y& Elsevier]

Most mammals use lateral sequence gaits during quadrupedal locomotion, a pattern characterized by the touchdown of a forelimb directly following the ipsilateral hind limb in a given stride cycle. Primates, however, tend to use diagonal sequence (DS) gaits, whereby it is the touchdown of a contralateral forelimb that follows that of a given hind limb most closely in time. A number of scenarios have been offered to explain why primates favor DS gaits, most of them relating to the use of the arboreal habitat and, in particular, the exploitation of a narrow branch niche. This experimental study explores the potential explanation for the use of DS gaits by examining the relationship between branch diameter and gait patterns in 360 strides collected from six species of quadrupedal strepsirrhine primates on broad and narrow diameter supports. Gait sequence is quantified using limb phase, or the percentage of time during a stride cycle that a forelimb touchdown follows an ipsilateral hind limb touchdown. Although Loris, Nycticebus and Eulemur rubriventer individuals in this study did exhibit significantly lower locomotor velocities on narrower supports (P<0.01 in all three species), analyses of covariance showed no significant differences in limb phase values between broad and narrow diameter supports. Hence, results indicate surprisingly little evidence to suggest that alterations in gait sequence pattern provide a specific advantage for negotiating narrow supports. Am. J. Primatol. 70:356–362, 2008. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

The aims of this study were to describe the curvature of anthropoid limb bones quantitatively, to determine how limb bone curvature scales with body mass, and to discuss how bone curvature influences static measures of bone strength. Femora and humeri in six anthropoid genera of Old World monkeys, New World monkeys, and gibbons were used. Bone length, curvature, and cross-sectional properties were incorporated into the analysis. These variables were obtained by a new method using three-dimensional morphological data reconstructed from consecutive CT images. This method revealed the patterns of curvature of anthropoid limb bones. Log-transformed scaling analyses of the characters revealed that bone length and especially bone curvature strongly reflected taxonomic/locomotor differences. As compared with Old World monkeys, New World monkeys and gibbons in particular have a proportionally long and less curved femur and humerus relative to body mass. It is also revealed that the section modulus relative to body mass varies less between taxonomic/locomotor groups in anthropoids. Calculation of theoretical bending strengths implied that Old World monkeys achieve near-constant bending strength in accordance with the tendency observed in general terrestrial mammals. Relatively shorter bone length and larger A-P curvature of Old World monkeys largely contribute to this uniformity. Bending strengths in New World monkeys and gibbons were, however, a little lower under lateral loading and extremely stronger and more variable under axial loading as compared with Old World monkeys, due to their relative elongated and weakly curved femora and humeri. These results suggest that arboreal locomotion, including quadrupedalism and suspension, requires functional demands quite dissimilar to those required in terrestrial quadrupedalism. [ABSTRACT FROM AUTHOR]

The foot has played a prominent role in evaluating early hominin locomotion. The calcaneus, in particular, plays an important role in weight-bearing. Although the calcanei of early hominins have been previously scrutinized, a three-dimensional analysis of the entire calcaneal shape has not been conducted. Here, we investigate the relationship between external calcaneal shape and locomotion in modern Homo sapiens (n = 130), Gorilla (n = 86), Pan (n = 112), Pongo (n = 31), Papio (n = 28), and hylobatids (Hylobates, Symphalangus ; n = 32). We use these results to place the calcanei attributed to Australopithecus sediba , A. africanus, A. afarensis, H. naledi , and Homo habilis/Paranthropus boisei into a locomotor context. Calcanei were scanned using either surface scanning or micro-CT and their external shape analyzed using a three-dimensional geometric morphometric sliding semilandmark analysis. Blomberg's K statistic was used to estimate phylogenetic signal in the shape data. Shape variation was summarized using a principal components analysis. Procrustes distances between all taxa as well as distances between each fossil and the average of each taxon were calculated. Blomberg's K statistic was small (K = 0.1651), indicating weak phylogenetic effects, suggesting variation is driven by factors other than phylogeny (e.g., locomotion or body size). Modern humans have a large calcaneus relative to body size and display a uniquely convex cuboid facet, facilitating a rigid midfoot for bipedalism. More arboreal great apes display relatively deeper cuboid facet pivot regions for increased midfoot mobility. Australopithecus afarensis demonstrates the most human-like calcaneus, consistent with obligate bipedalism. Homo naledi is primarily modern human-like, but with some intermediate traits, suggesting a different form of bipedalism than modern humans. Australopithecus africanus , A. sediba , and H. habilis/P. boisei calcanei all possess unique combinations of human and nonhuman ape-like morphologies, suggesting a combination of bipedal and arboreal behaviors. [ABSTRACT FROM AUTHOR]

Mother-infant dyads were observed among three populations of rhesus monkeys (Macaca mulatta) in India and Nepal. This research had three purposes: 1) to examine the influences of maternal activities (ie, feeding, locomotion, and rest) and arboreality on the early development of infant independence; 2) to determine whether interpopulation differences in the development of infant independence, can be accounted for by correlated differences in maternal time budgets and the amount of time infants spent on the ground; and 3) to explore how patterns of maternal care may or may not mitigate increased risk of infant mortality resulting from human harassment. Despite significant interpopulation differences in maternal time budgets, the amount of time infants spent on the ground, and the degree of harassment the animals experienced, few interpopulation differences in infant development could be found. The application of a multiple regression/correlation analysis revealed that the development of infant independence was affected by the above factors but that those factors were acting in complementary ways to constrain development and to minimize the differences across populations. [ABSTRACT FROM AUTHOR]