Evaluating the muscle attachment hypothesis for sagittal cresting in Gorilla and Pongo.

Primate mandibular morphology is often associated with jaw functionality of the masticatory complex in the context of variation in diets. Recent research into the disparities between the diet and jaw functionality in male and female hominoids is inconclusive and suggests that sexual dimorphism in the mandible may be influenced by external factors such as temporalis and masseter muscle morphology, which in turn may be influenced by sexual selection. As the muscles associated with mastication (i.e., the type of chewing exhibited by primates and other mammals) encompass the mandible as well as the neurocranium, including the sagittal crest among some individuals, this study investigates sex-specific associations between regions of the mandibular ramus and neurocranium associated with mastication in a dentally mature sample of Gorilla and Pongo. A total of four cranial and mandibular variables were measured in two Gorilla taxa (Gorilla gorilla gorilla and Gorilla beringei graueri) and one Pongo taxon (Pongo pygmaeus pygmaeus) (n = 220). For all three taxa, we investigate (a) whether the degree of sexual dimorphism in cranial regions associated with sagittal cresting (sagittal crest size (SCS) and temporalis muscle attachment area (TMAA)) is proportional to the degree of mandibular ramus area (MRA) and coronoid process height (CPH) sexual dimorphism, (b) whether there are sex differences in scaling relationships between TMAA and MRA, and (c) whether there are sex differences in the strength of association between TMAA and CPH. We show that for G. g. gorilla, variables associated with sagittal cresting show higher sexual dimorphism values than our two mandibular ramus variables, which is not the case for G. b. graueri or for P. p. pygmaeus. All three taxa show similar sex-specific scaling relationships between TMAA and MRA, where for males this relationship does not diverge from isometry, and for females there is a negative allometric relationship. Our findings also show intraspecific sex differences in allometric slopes between MRA and TMAA for all three taxa. Only G. g. gorilla shows a significant association between TMAA and CPH, which is observed in both sexes. Although there are some statistical associations between the cranial and mandibular regions associated with mastication, our results show that among male gorillas and orangutans, patterns of variation in the sagittal crest, TMAA, mandibular ramus and the coronoid process cannot be explained by the muscle attachment hypothesis alone. These findings have implications surrounding the associations between social behaviour and the morphology of the craniofacial complex.

An evaluation of interactive projections as digital enrichment for orangutans.

Digital technologies are increasingly being incorporated into the provision of enrichment for captive primates, ranging from the ad-hoc use of iPads to specifically designed hardware installed in the design of new exhibits. In this article, we present a digital enrichment system that utilizes a novel approach with interactive projections, installed in the orangutan exhibit at Melbourne Zoo. While previous research into orangutan enrichment has involved reinforcement using food rewards, this study is the first investigation of digital enrichment for orangutans that does not involve food rewards. Rather, the interactive projections were designed to provide intrinsically rewarding environmental enrichment, instead of a cheaper or more variable way of delivering food. Our observations of orangutans' use of the system supports the approach of using interactive projections, finding that it is more responsive than capacitance or resistive based touch-screen technologies to the variety of ways that orangutans "touch": with whole hands, feet, faces, and with objects. We also present the results from a preliminary study into the effect of this enrichment into orangutan behavior which found presence or use of the device did not affect time spent engaged in the majority of behaviors of the individuals studied.

Grouping behavior of Sumatran orangutans (Pongo abelii) and Tapanuli orangutans (Pongo tapanuliensis) living in forest with low fruit abundance.

In contrast to the African great apes, orangutans (Pongo spp.) are semisolitary: Individuals are often on their own, but form aggregations more often than expected by chance. These temporary aggregations provide social benefits such as mating opportunities. When fruit availability is high, costs of aggregating should be lower, because competition is less pronounced. Therefore, average party size is expected to be higher when fruit availability is high. This hypothesis would also explain why orangutans in highly fruit-productive habitats on Sumatra are more gregarious than in the usually less productive habitats of Borneo. Here, we describe the aggregation behavior of orangutans in less productive Sumatran habitats (Sikundur and Batang Toru), and compare results with those of previously surveyed field sites. Orangutans in Sikundur were more likely to form parties when fruit availability was higher, but the size of daily parties was not significantly affected by fruit availability. With regard to between-site comparisons, average party sizes of females and alone time of parous females in Sikundur and Batang Toru were substantially lower than those for two previously surveyed Sumatran sites, and both fall in the range of values for Bornean sites. Our results indicate that the assessment of orangutans on Sumatra as being more social than those on Borneo needs revision. Instead, between-site differences in sociality seem to reflect differences in average fruit availability.

The ligamentum teres femoris in orangutans.

OBJECTIVES: It is widely viewed that orangutans lack a ligamentum teres femoris (LTF) inserting on the femoral head because orangutans lack a distinct fovea capitis. Orangutans employ acrobatic quadrumanous clambering that requires a high level of hip joint mobility, and the absence of an LTF is believed to be an adaptation to increase hip mobility. However, there are conflicting reports in the literature about whether there may be a different LTF configuration in orangutans, perhaps with a ligament inserting on the femoral neck instead. Here we perform a dissection-based study of orangutan hip joints, assess the soft tissue and hard tissue correlates of the orangutan LTF, and histologically examination the LTF to evaluate whether it is homologous to that found in other hominoids. MATERIALS AND METHODS: The hip joints from six orangutans were dissected. In the two orangutans with an LTF passing to the femoral head, the LTF was assessed histologically. Skeletonized femora (n=56) in osteological repositories were examined for evidence of a foveal pit. RESULTS: We observed an LTF in two of the three infant orangutans but not in the sub-adult or adult specimens. Histological examination of the infant LTF shows a distinct artery coursing through the LTF to the head of the femur. One percent of orangutan femora present with a foveal scar, but no pit, on the femoral head. DISCUSSION: Despite being absent in adults, the LTF is present in at least some orangutans during infancy. We suggest that the LTF maintains a role in blood supply to the femoral head early in life. Because the LTF can limit hip mobility, this may explain why the LTF may be lost as an orangutan ages and gains locomotor independence. These findings enhance our understanding of orangutan hip morphology and underscore the need for future soft tissue investigations.

Stillbirth rates across three ape species in accredited American zoos.

Stillbirths, or births of infants that died in the womb, represent a failure of the materno-feto-placental unit to maintain a suitable fetal environment. Typical studies of nonhuman primate (NHP) stillbirth patterns are primarily descriptive and focus on macaques (genus Macaca). Thus, less is known about other NHP species and rarer still are studies that examine possible biological factors that influence stillbirth rates across taxa. To examine possible contributors to stillbirths in great apes, we analyzed 36 years (1980-2016) of historical data documenting births of zoo-housed chimpanzees (Pan troglodytes, N = 391), western lowland gorillas (Gorilla gorilla gorilla, N = 491), and orangutans (Pongo spp, N = 307) in accredited zoological parks in the United States. The average number of births for each of the 446 mothers was 2.7, resulting in a total of 1,189 births with 143 stillbirths (12%). Stillbirths represented 12% of chimpanzee births, 13% of gorilla births, and 10% of orangutan births. We used generalized linear mixed-effects models to assess possible relationships between stillbirth likelihood and mother origin (wild- versus captive-born), age, and genus. Across taxa, older mothers were more likely to have a stillbirth (p = 0.004). While these results are likely influenced by both biological and management-related factors (e.g., selective captive breeding), they may be useful to population managers in evaluating pregnancy risks for great apes. Captive settings and archival studbook data such as these may provide a unique opportunity to further explore this topic.

Manual function and performance in humans, gorillas, and orangutans during the same tool use task.

OBJECTIVES: Humans are known to possess more complex manual abilities than other primates. However, the manual abilities of primates have not been fully explored, and we still do not know if the manipulative abilities we attribute to humans are unique. The aim of this study was to compare the manual function and performance developed by humans, gorillas and orangutans while performing the same experimental tool use task. MATERIALS AND METHODS: The study was conducted on 20 humans, 6 gorillas, and 7 orangutans. Each individual had to use a tool to collect food from a maze during six experimental sessions while maintaining the same unconstrained body posture condition. We quantified the different manual techniques used and the manual performance. RESULTS: Each species used different techniques. Humans used bimanual grip techniques, pad-to-pad precision grasping postures, and in-hand movements involving fingertips. Gorillas used unimanual grip techniques and simple in-hand movements while orangutans used a variety of strategies (e.g., hand or mouth). With these techniques, humans performed the task better than both gorillas and orangutans (e.g., by being quicker to collect the food). DISCUSSION: This study highlights other ways in which humans' manual dexterity differs from that of other species and emphasizes the distinct manipulative function of orangutans. The differences between the species could be due to the differing muscular anatomy and morphology of the hands, with hand proportion possibly placing particular biomechanical constraints on each species. The differences between gorillas and orangutans could result from their different locomotor behaviors, and we hypothesize terrestriality facilitates the development of complex manipulation.

Immunoglobulin A and nutrients in milk from great apes throughout lactation.

Differences in macronutrients between human and ape milks appear relatively small, but variation in other components such as immunoglobulins (Ig) may be greater. This study characterized the macronutrient and secretory (sIgA) profiles in milk from gorillas and orangutans throughout lactation. Fifty-three milk samples from four gorillas and three orangutans were collected throughout 48 and 22 months postpartum (MPP), respectively. Samples were grouped in five stages of lactation (0 to 6 months, more than 6 months to 12 months, more than 12 months to 18 months, more than 18 months to 36 months, and more than 36 months to 48 months). Data were analyzed as a complete randomized design. Concentration of sIgA did not change due to species or its interaction with MPP. Crude protein, regardless of MPP, was greater for gorillas compared with orangutans (1.27 vs. 0.85%). Fat, sugar, and gross energy were affected by the interaction of species × MPP. For gorilla milk, concentrations of sIgA were 43 mg/L at 6 MPP increasing to 79 mg/L at 48 MPP. Protein was highest at 48 MPP. Sugar was lowest at 48 MPP. Values for fat and gross energy were the highest 36 MPP. For orangutan milk, concentrations of sIgA were highest at 6 MPP. Sugar decreased with MPP. Protein, dry matter, or fat were unaffected by MPP. Gross energy content was steady during the first 18 MPP but it tended to decrease by 36 MPP. The results indicate that macronutrients are similar between human, published data, and great ape milk, though gorilla milk has higher protein and human milk higher fat (published data). Concentrations of sIgA in ape milk were about 10-fold lower than human values from the literature. Differences between human and ape milk may lie more in bioactive/immune molecules than nutrients. RESEARCH HIGHLIGHTS: Milk macronutrients from great apes differed throughout lactation. Milk macronutrients but not IgA from non-human great apes and humans were quite similar. Milk protein was greater in Gorilla compared with Orangutan.

Young children spontaneously invent wild great apes' tool-use behaviours.

The variety and complexity of human-made tools are unique in the animal kingdom. Research investigating why human tool use is special has focused on the role of social learning: while non-human great apes acquire tool-use behaviours mostly by individual (re-)inventions, modern humans use imitation and teaching to accumulate innovations over time. However, little is known about tool-use behaviours that humans can invent individually, i.e. without cultural knowledge. We presented 2- to 3.5-year-old children with 12 problem-solving tasks based on tool-use behaviours shown by great apes. Spontaneous tool use was observed in 11 tasks. Additionally, tasks which occurred more frequently in wild great apes were also solved more frequently by human children. Our results demonstrate great similarity in the spontaneous tool-use abilities of human children and great apes, indicating that the physical cognition underlying tool use shows large overlaps across the great ape species. This suggests that humans are neither born with special physical cognition skills, nor that these skills have degraded due to our species' long reliance of social learning in the tool-use domain.

Orangutans (Pongo spp.) have deeper, more efficient sleep than baboons (Papio papio) in captivity.

The nightly construction of arboreal sleeping platforms or "nests" has been observed among every great ape population studied to date. However, this behavior has never been reported in any other nonhuman primate and comparisons between ape and monkey sleep illuminate the link between sleeping substrates, positional behavior, and sleep efficiency. Here, we compare sleep depth and efficiency and night-time positional behavior between a large-bodied cercopithecoid (Papio papio) and a large-bodied hominoid (Pongo spp.) at the Indianapolis Zoo. We used infrared videography to assess nightly sleep and awake behavioral states, gross body movements, and postures in baboons (N = 45 nights) and orangutans (N = 128 nights). We calculated the total waking time, total sleep time, sleep fragmentation (the number of brief awakenings ≥2 min/h), sleep motor activity (number of motor activity bouts per hour), sleep efficiency (sleep duration/time in bed), and percentage of time spent in each posture. By every measure, orangutans experienced overall deeper, more efficient sleep. Baboons were more likely to sleep in guarded, upright positions (weight bearing on their ischial callosities) and never opted to use additional materials to augment sleep environments, whereas orangutans slept in insouciant, relaxed positions on constructed sleeping materials. Our results suggest that relaxed sleeping postures may have been enabled by sleeping platforms as a behavioral facilitator to sleep, which could have allowed for greater sleep depth and next-day cognitive capacities in both great apes and hominins.

Pre-Sleep and Sleeping Platform Construction Behavior in Captive Orangutans (Pongo spp.): Implications for Ape Health and Welfare.

The nightly construction of a 'nest' or sleeping platform is a behavior that has been observed in every wild great ape population studied, yet in captivity, few analyses have been performed on sleep related behavior. Here, we report on such behavior in three female and two male captive orangutans (Pongo spp.), in a natural light setting, at the Indianapolis Zoo. Behavioral samples were generated, using infrared cameras for a total of 47 nights (136.25 h), in summer (n = 25) and winter (n = 22) periods. To characterize sleep behaviors, we used all-occurrence sampling to generate platform construction episodes (n = 217). Orangutans used a total of 2.4 (SD = 1.2) techniques and 7.5 (SD = 6.3) actions to construct a sleeping platform; they spent 10.1 min (SD - 9.9 min) making the platform and showed a 77% preference for ground (vs. elevated) sleep sites. Comparisons between summer and winter platform construction showed winter start times (17:12 h) to be significantly earlier and longer in duration than summer start times (17:56 h). Orangutans should be provisioned with seasonally appropriate, high quality materials suitable for construction of sleeping platforms to increase sleep quality and improve animal health and welfare.

Effect of partial covering of the visitor viewing area window on positioning and orientation of zoo orangutans: A preference test.

The window of the visitor viewing area adjacent to an animal platform in an orangutan enclosure was altered to produce three viewing treatments in a randomized controlled experiment. These treatments were window uncovered, left side of the window covered or right side of the window covered. Observations were conducted on the orangutans present on the platform, and on their location (left or right side), and orientation (towards or away from the window) while on the platform. The partial covering of the window had little effect on the proportion of time orangutans spent on the viewing platform, or on the direction they faced when on the platform. When the orangutans were facing towards the window, and the right side was uncovered, irrespective of whether the left side was covered, they spent about three quarters of the time on the right side, suggesting a preference for the right side of the platform. However, when the right side was covered and the left side uncovered, the animals facing towards the window spent only about a quarter of the time on the right side, that is, they spent more time on the uncovered side. The results suggest that the orangutans have a preference to position themselves to face the window of the visitor viewing area.

Food mechanical properties, feeding ecology, and the mandibular morphology of wild orangutans.

Bornean orangutan mandibular morphology has been functionally linked to the exploitation of hard and tough foods, based on evidence that Pongo pygmaeus wurmbii spends a greater percentage of time feeding on bark, seeds and vegetation compared with Pongo abelii (Sumatran orangutans) and the assumption that these tissues are more challenging to process than fruit pulp. We measured and compared toughness (R) and Young's modulus (E) of ripe and unripe foods exploited by P. abelii and P. p. wurmbii. Additionally, we recorded and compared the percentage of time these orangutans fed on plants/plant parts of varying degrees of R and E. Compared with P. abelii, P. p. wurmbii consumed significantly tougher and more displacement limited (R/E)(0.5) fruit parts, leaves and inner bark, and spent a significantly greater percentage of time feeding on immature leaves, unripe fruit and other vegetation. Modulus did not vary as expected between species, likely because we failed to capture the high-end range of modulus values for tissues consumed by P. p. wurmbii. Notably, P. p. wurmbii spent ∼40% of its feeding time on the toughest foods consumed (between 1000 and 4000 J m(-2)). Thus, the hypothesis that mandibular robusticity in P. p. wurmbii is functionally linked to feeding on tough foods is supported and is likely related to countering relatively larger external forces and/or repetitive loads required to process the toughest tissues. The importance of elastic modulus on morphological divergence awaits future studies capturing the full range of this material property for P. p. wurmbii. Finally, phenophase and fruit availability influence orangutan species differences in food material properties and percentage of time spent feeding on various foods, emphasizing the importance of incorporating these variables in future studies of feeding ecology and craniodental morphology in extant taxa.

Orangutan fish eating, primate aquatic fauna eating, and their implications for the origins of ancestral hominin fish eating.

This paper presents new evidence of fish eating in rehabilitant orangutans living on two Bornean islands and explores its contributions to understanding nonhuman primates' aquatic fauna eating and the origins of ancestral hominin fish eating. We assessed the prevalence of orangutans' fish eating, their techniques for obtaining fish, and possible contributors (ecology, individual differences, humans). We identified 61 events in which orangutans tried to obtain fish, including 19 in which they ate fish. All the orangutans were juvenile-adolescent; all the fish were disabled catfish; and most were obtained and eaten in drier seasons in or near shallow, slow-moving water. Orangutans used several techniques to obtain fish (inadvertent, opportunistic and deliberate hand-catch, scrounge, tool-assisted catch) and probably learned them in that order. Probable contributing factors were orangutan traits (age, pre-existing water or tool skills), island features (social density, water accessibility), and local human fishing. Our review of primates' aquatic fauna eating showed orangutans to be one of 20 species that eat aquatic fauna, one of nine confirmed to eat fish, and one of three that use tools to obtain fish. Primate fish eating is also site-specific within species, partly as a function of habitat (e.g., marine-freshwater, seasonality) and human influence (possibly fostered eating fish or other aquatic fauna at most sites, clearly induced it at some). At tropical freshwater sites, fish eating occurred most often in drier seasons around shallow water. Orangutan and primate findings are generally consistent with Stewart's (2010) reconstruction of the origins of ancestral hominin fish eating, but suggest that it, and tool-assisted fish catching, were possible much earlier.

Variation in perikymata counts between repetitive episodes of linear enamel hypoplasia among orangutans from Sumatra and Borneo.

The goal of this study is to evaluate whether repetitive linear enamel hypoplasia (rLEH) in apes is ecologically informative. LEH, which appears as grooves of thinner enamel often caused by malnutrition and/or disease, is a permanent record of departures from developmental homeostasis in infant and juvenile apes. Orangutans were selected for the study as they are a threatened species, have a remarkably high prevalence of rLEH, and because Sumatra is deemed a better habitat for orangutans than is Borneo, facilitating an ecological comparison. Objectives are to determine: a) whether periodicity of rLEH in orangutans corresponds to monsoon-mediated cycles in precipitation or food; and b) whether patterning of rLEH supports the view that Borneo is an inferior habitat. This study compares the counts of perikymata between adjacent LEH from 9 Sumatran and 26 Bornean orangutans to estimate the periodicity of rLEH. A total of 131 nonredundant inter-LEH perikymata counts were transformed to natural log values to reveal clusters of counts in a multiplicative series. Using a value of 10 days to form one perikyma, rLEH tends to recur semiannually in both populations. However, Sumatran orangutans show significantly fewer semiannual intervals and more annually recurring episodes. Bornean orangutans show mostly semiannual intervals and are more variable in inter-LEH perikymata counts. It is concluded that: a) developmental conditions for infant orangutans in Sumatra protect them somewhat from seasonal and environmental variation; b) temporal patterning of rLEH indicates that Borneo is the poorer habitat for orangutans; and c) the study of rLEH can be ecologically informative.

Evaluating the conservation impact of an innovative zoo-based educational campaign: 'Don't Palm Us Off' for orang-utan conservation.

With significant biodiversity loss occurring presently, increased emphasis is being placed upon the capacity of zoos to contribute to species conservation. This paper evaluates an innovative conservation education campaign 'Don't Palm Us Off' implemented at Melbourne Zoo, Australia. This sought to address a lack of public awareness regarding palm oil (the product most threatening the survival of the orang-utan) and to create public support for mandatory labeling of palm oil on food products, allowing for informed consumer purchasing. Communication tools utilized included an educational video presentation played on-site, as well as You Tube video, celebrity ambassadors, and social media. Evaluation took place across four time-points: baseline, mid-point, conclusion (12 months), and follow-up. Zoo visitors (N = 403) were randomly selected whilst visiting the orang-utan exhibit, completing a questionnaire regarding knowledge about orangutans, attitudes toward orangutans, support for palm oil labeling, previous conservation behavior, and intentions for future behavior. Results revealed significant increases in palm oil awareness; attitudes toward orangutans; support for palm oil labeling; and indicating labeling would influence purchasing behavior, at all times relative to baseline (P < 0.01). There were also significant increases in self-reported conservation behavior at the end of the campaign and follow-up (P < 0.05). In excess of 160,000 people additionally signed an associated petition for mandatory palm oil labeling. Overall the findings support the efficacy of this multi-faceted initiative; highlighting the importance of continued innovation in zoo-based conservation education and practice (including the integration of emerging technologies with traditional on-site education) to maximize contributions to species conservation.

Dynamic inconsistency in great apes.

When presented with the option of either an immediate benefit or a larger, later reward, we may behave impatiently by choosing instant gratification. Nonetheless, when we can make the same decision ahead of time and plan for the future, we tend to make more patient choices. Here, we explored whether great apes share this core feature of human decision-making, often referred to as dynamic inconsistency. We found that orangutans, bonobos, and gorillas tended to act impatiently and with considerable variability between individuals when choosing between an immediate reward and a larger-later reward, which is a commonly employed testing method in the field. However, with the inclusion of a front-end delay for both alternatives, their decisions became more patient and homogeneous. These results show that great apes are dynamically inconsistent. They also suggest that, when choosing between future outcomes, they are more patient than previously reported. We advocate for the inclusion of diverse time ranges in comparative research, especially considering the intertwinement of intertemporal choices and future-oriented behavior.

The evolution of compliance in the human lateral mid-foot.

Fossil evidence for longitudinal arches in the foot is frequently used to constrain the origins of terrestrial bipedality in human ancestors. This approach rests on the prevailing concept that human feet are unique in functioning with a relatively stiff lateral mid-foot, lacking the significant flexion and high plantar pressures present in non-human apes. This paradigm has stood for more than 70 years but has yet to be tested objectively with quantitative data. Herein, we show that plantar pressure records with elevated lateral mid-foot pressures occur frequently in healthy, habitually shod humans, with magnitudes in some individuals approaching absolute maxima across the foot. Furthermore, the same astonishing pressure range is present in bonobos and the orangutan (the most arboreal great ape), yielding overlap with human pressures. Thus, while the mean tendency of habitual mechanics of the mid-foot in healthy humans is indeed consistent with the traditional concept of the lateral mid-foot as a relatively rigid or stabilized structure, it is clear that lateral arch stabilization in humans is not obligate and is often transient. These findings suggest a level of detachment between foot stiffness during gait and osteological structure, hence fossilized bone morphology by itself may only provide a crude indication of mid-foot function in extinct hominins. Evidence for thick plantar tissues in Ardipithecus ramidus suggests that a human-like combination of active and passive modulation of foot compliance by soft tissues extends back into an arboreal context, supporting an arboreal origin of hominin bipedalism in compressive orthogrady. We propose that the musculoskeletal conformation of the modern human mid-foot evolved under selection for a functionally tuneable, rather than obligatory stiff structure.

First discovery of Pleistocene orangutan (Pongo sp.) fossils in Peninsular Malaysia: biogeographic and paleoenvironmental implications.

Nine isolated fossil Pongo teeth from two cave sites in Peninsular Malaysia are reported. These are the first fossil Pongo specimens recorded in Peninsular Malaysia and represent significant southward extensions of the ancient Southeast Asian continental range of fossil Pongo during two key periods of the Quaternary. These new records from Peninsular Malaysia show that ancestral Pongo successfully passed the major biogeographical divide between mainland continental Southeast Asia and the Sunda subregion before 500 ka (thousand years ago). If the presence of Pongo remains in fossil assemblages indicates prevailing forest habitat, then the persistence of Pongo at Batu Caves until 60 ka implies that during the Last Glacial Phase sufficient forest cover persisted in the west coast plain of what is now Peninsular Malaysia at least ten millennia after a presumed corridor of desiccation had extended to central and east Java. Ultimately, environmental conditions of the peninsula during the Last Glacial Maximum evidently became inhospitable for Pongo, causing local extinction. Following post-glacial climatic amelioration and reforestation, a renewed sea barrier prevented re-colonization from the rainforest refugium in Sumatra, accounting for the present day absence of Pongo in apparently hospitable lowland evergreen rainforest of Peninsular Malaysia. The new teeth provide further evidence that Pongo did not undergo a consistent trend toward dental size reduction over time.

Rotator cuff muscle function and its relation to scapular morphology in apes.

It is widely held that many differences among primate species in scapular morphology can be functionally related to differing demands on the shoulder associated with particular locomotor habits. This perspective is largely based on broad scale studies, while more narrow comparisons of scapular form often fail to follow predictions based on inferred differences in shoulder function. For example, the ratio of supraspinous fossa/infraspinous fossa size in apes is commonly viewed as an indicator of the importance of overhead use of the forelimb, yet paradoxically, the African apes, the most terrestrial of the great apes, have higher scapular fossa ratios than the more suspensory orangutan. The recent discovery of several nearly complete early hominin scapular specimens, and their apparent morphological affinities to scapulae of orangutans and gorillas rather than chimpanzees, has led to renewed interest in the comparative analysis of human and extant ape scapular form. To facilitate the functional interpretation of differences in ape scapulae, particularly in regard to relative scapular fossa size, we used electromyography (EMG) to document the activity patterns in all four rotator cuff muscles in orangutans and gibbons, comparing the results with previously published data for chimpanzees. The EMG results indicate that the distinctive contributions of each cuff muscle to locomotion are the same in the three ape species, failing to support inferences of differences in rotator cuff function based on relative scapular fossa size comparisons. It is also shown that relative scapular fossa size is not in fact a good predictor of either the relative masses or cross-sectional areas of the rotator cuff muscles in apes, and relative fossa size gives a false impression of the importance of individual cuff muscles to locomotor differences among apes. A possible explanation for the disparity between fossa and muscle size relates to the underappreciated role of the scapular spine in structural reinforcement of the blade.

Orangutan (Pongo spp.) whistling and implications for the emergence of an open-ended call repertoire: a replication and extension.

One of the most apparent discontinuities between non-human primate (primate) call communication and human speech concerns repertoire size. The former is essentially fixed to a limited number of innate calls, while the latter essentially consists of numerous learned components. Consequently, primates are thought to lack laryngeal control required to produce learned voiced calls. However, whether they may produce learned voiceless calls awaits investigation. Here, a case of voiceless call learning in primates is investigated--orangutan (Pongo spp.) whistling. In this study, all known whistling orangutans are inventoried, whistling-matching tests (previously conducted with one individual) are replicated with another individual using original test paradigms, and articulatory and acoustic whistle characteristics are compared between three orangutans. Results show that whistling has been reported for ten captive orangutans. The test orangutan correctly matched human whistles with significantly high levels of performance. Whistle variation between individuals indicated voluntary control over the upper lip, lower lip, and respiratory musculature, allowing individuals to produce learned voiceless calls. Results are consistent with inter- and intra-specific social transmission in whistling orangutans. Voiceless call learning in orangutans implies that some important components of human speech learning and control were in place before the homininae-ponginae evolutionary split.