Sagittal crests are observed among some primate species, including early extinct hominins, however the majority of research investigating sagittal cresting among extant primates has been confined to catarrhines. Sagittal cresting has not been well-investigated among capuchin monkeys, and understanding whether there are taxonomic differences in the frequency and pattern of sagittal cresting among gracile and robust capuchin species, or whether sagittal crest expression is only confined to the males of some species, may yield important insights in a comparative context, to better understand the underlying basis for the frequency and pattern of sagittal cresting among australopithecine species. In the research presented here, I investigate whether there are interspecific differences in the frequency and pattern of sagittal cresting, and sexual dimorphism in cresting frequency among six capuchin species, representing three gracile capuchin species (Cebus albifrons, Cebus capucinus and Cebus olivaceus) and three robust capuchin species (Cebus apella, Cebus macrocephalus and Cebus libidinosus). I collected sagittal cresting data for 279 dentally mature cranial specimens using 3D models. There are interspecific differences in the frequency of sagittal cresting among capuchin species, with four out of the six species investigated (C. capucinus, C. apella, C. macrocephalus and C. libidinosus) showing sagittal crests. There are significant sex differences in the frequency of sagittal cresting in C. capucinus and robust capuchin species (C. apella, C. libidinosus, C. macrocephalus). I further show that there are interspecific differences in the pattern of sagittal cresting among the four species that exhibit sagittal crests. Sagittal cresting in C. capucinus occurs in the posterior region of the neurocranium, in contrast to the robust capuchin species, whose sagittal crests mainly extend from anterior to bregma, to the posterior cranial region at the midline. The underlying reasons for interspecific and sex differences in the frequency and pattern of sagittal cresting among species are yet to be elucidated, and may be associated with dietary, habitat or socioecological differences among capuchin groups.

Touch has a significant impact on the development of infant primates, but it is still understudied. Little is reported, for example, about the effect of infants' touch on their environment and social development. In this study, we sought to fill this gap by investigating the touch of capuchin monkey (Sapajus libidinosus) infants on the faces of other individuals in the group. We followed eight wild infants (four females and four males) across their first 3 years of life and assessed whether this behavior is part of the social repertoire and whether it facilitates facial recognition. We coded all social events of the infants in 127.3 hr of video recorded weekly from birth until 36 months, through daily focal sampling. We recorded motor patterns of the behavior, the context, the partner touched, and the partners' response to each infant face touching. We found that touching was always associated with affiliative contexts. Infant face touching of other group members was associated with lipsmacking and grooming, consistently involving visual contact and exploration of the face by the infant's hand. In this species, face touching also occurred in response to engagement initiated by the touched individual, potentially signaling reciprocity in affiliative interactions and serving as a pleasurable gesture. (PsycInfo Database Record (c) 2025 APA, all rights reserved).

Supplemental Material for Touching Faces: The Active Role of Infant Capuchin Monkeys (Sapajus libidinosus) in Their Social Development

Predation influences foraging strategies, as primates must avoid being preyed on while feeding. Some populations of capuchin monkeys are the only neotropical primates that customarily use the ground for nut-cracking. This time-consuming and focus-demanding foraging activity may increase susceptibility to predation events. However, there is currently no data on predation in tool-using Sapajus populations. We report a snake’s (Boa constrictor) predatory attack on a bearded capuchin monkey (S. libidinosus) in a tool-using population, as well as the other monkeys’ alarm calling and threat displays. We confirm these monkeys’ predation vulnerability and discuss how they balance foraging requirements with predation risk.

ABSTRACTObjectivesA hallmark of hominin evolution is the advent and diversification of stone tool use, and biological anthropologists have a particular interest in characterizing tool use behaviors in different hominin species. Robust capuchins, the genus Sapajus, are an excellent convergent model system for understanding tool use evolution, principally in the context of foraging, in terms of how they use stones to process hard fruits. However, most published studies of capuchin tool use in the wild focus on the species Sapajus libidinosus. In order to strengthen comparative analyses, it is important to do research across robust capuchin species to understand tool use capacities and variation across the genus. The first indirect evidence that reported tool use in wild S. xanthosternos was in 2009, but since that time no additional publications have described this behavior for this species. In this study we provide the first complete characterization of tool use in wild S. xanthosternos for two areas within Montes Claros, Minas Gerais state, Brazil: Santa Rosa de Lima district, and Lapa Grande State Park. We compare our findings to the stone tool use characteristics reported in wild Sapajus libidinosus and other capuchin monkey species.Materials and MethodsIn monthly surveys from January to September 2018, we walked trails through the two study areas and categorized tool use site characteristics, including anvil area, height, and perimeter; hammer stone weight; and species of fruit utilized. Additionally, we utilized camera traps at high‐use sites.ResultsWe describe the tools used by S. xanthosternos at 169 sites clustered in seven Nutcracking Areas, for processing three different species of encased fruit: Macaúba (Acrocomia aculeata), Cansaçao (Cnidoscolus pubescens), and Guariroba (Syagrus oleracea). With camera traps, we directly observed tool use behavior for the first time in this species.DiscussionSapajus xanthosternos displayed tool use patterns very similar to those of S. libidinosus. The main difference was in regards to physical force; in our study, the mean weight of stones used by S. xanthosternos was higher than the mean reported for S. libidinosus at most field sites; however, there was no difference in hammer weight between S. libidinosus and S. xanthosternos when hammering Macaúba. We also registered the heaviest hammer stone for tool use (7.675 kg) known for the robust capuchin genus. It is clear from our study that tool use capacity and characteristics are conserved across the radiation of extant Sapajus, suggesting a possible stone tool use cognitive capacity spanning up to 3.3 million years of diversification within this genus. Unlike stone tool use occurring throughout the year for S. libidinosus, at our study sites S. xanthosternos used nutcracking tools only during the dry season.

The evolution of hand ability in primates is staged, with the visual control of hand shaping likely originating in Platyrrhine primates, members of a monophyletic primate suborder whose stem group diverged from catarrhines about 40 million years ago. Platyrrhine hand shaping may have evolved in relation to visually mediated inhand food manipulation and hand withdraw to the mouth for eating movements. The present study examines this hypothesis in the Platyrrhine Sapajus libidinosus, the bearded capuchin monkey. These monkeys include the tuber raiz de macaco, or monkey’s root, in their diet, a food item that poses challenges in handling, peeling and eating. Analysis of video recordings show that the capuchins used vision to render the tuber into fibers and roots that could be chewed and ingested. Visual engagement was initiated as each rendering/eating sequence began and visual disengage, with a blink and head raise, occurred just before a tuber reached the mouth. Two-handed withdraws mainly brought intact tubers to the incisors for peeling and shredding and one-handed withdraws mainly brought tuber fibers and roots that protrude from the hand to the premolars for chewing. The capuchins made use of novel power hand grasps, featuring the digit tips pressing food items against the interdigit pads and palm. They displayed individual but not group preference in pulling and holding the tubers with one hand and manipulating the tuber at the mouth with the other hand. The results are discussed in relation to the idea that the evolution of the visual and cognitive skills associated with inhand food handling to the changing affordance of food facilitates its management by the mouth. This visuomanual skill could be applied to other functions including tool use.

Primates employ different tools and techniques to overcome the challenges of obtaining underground food resources. Humans and chimpanzees are known to tackle this problem with stick tools and one population of capuchin monkeys habitually uses stone tools. Although early hominids could have used stones as digging tools, we know little about when and how these could be useful. Here, we report a second primate population observed using stone tools and the first capuchin monkey population to habitually use the ‘stick-probing’ technique for obtaining underground resources. The bearded capuchin monkeys (Sapajus libidinosus) from Ubajara National Park, Brazil, use ‘hands-only’ and ‘stone-digging’ techniques for extracting underground storage organs and trapdoor spiders. Males also use ‘stick-probing’ and ‘stone-stick’ techniques for capturing trapdoor spiders. Tool use does not increase success in obtaining these resources. Stone-digging is less frequent in this population than in the only other known population that uses this technique. Females use stones in a lower proportion of their digging episodes than males in both populations. Ecological and cultural factors potentially influence technique choice and sex differences within and between populations. This population has a different pattern of underground food exploration using tools. Comparing this population with others and exploring the ecological and cultural factors under which capuchin monkeys employ different tools and techniques will allow us to better understand the pressures that may have shaped the evolution of those behaviors in primates.

Introduction: Bearded capuchins display a wide variety of manipulatory skills and make routine use of tools in both captivity and the wild. The efficient handling of objects in this genus has led several investigators to assume near-human thumb movements, despite a lack of anatomical studies. Methods: Here, we performed an anatomical analysis of muscles and bones in the capuchin hand. Sapajus morphological traits were quantitatively compared with those of humans, chimpanzees, gorillas, and baboons. Results: The comparative analysis indicated that the Sapajus hand is more similar to that of baboons and least similar to that of humans according to the muscles, bones, and three-dimensional data. Furthermore, these findings suggest that bearded capuchins lack true thumb opponency. Regarding manipulatory skills, they display rather primitive hand traits, with limited resources for precision grasping using the opponens pollicis. Discussion: These findings suggest that bearded capuchins' complex use of tools depends more heavily on their high cognitive abilities than on a versatile hand apparatus. These findings offer crucial insights into the evolution of primate cognition.

Populations of bearded capuchin monkeys (Sapajus libidinosus) vary in their tool use behaviors, with some of this divergence regarded as culturally determined. The use of stone tools, primarily to crack open encased foods, is widespread among bearded capuchins living in dry habitats (Caatinga and Cerrado). Significant diversity in targets, processed foods, material, and size of tools is observed across populations. However, so far, only a few sites have been systematically studied, and we are still distant from a representative picture of the range of variation in capuchins' culture. In this study, we did a systematic assessment of stone tool use sites in the Ubajara National Park (UNP), in the Caatinga region of Ceará, Brazil, recording and measuring stone tools, processed foods, and available lithic resources as part of an extensive comparative research, the CapCult project. We found indirect and direct evidence that capuchin monkeys at UNP customarily use hammerstones and anvils to process at least two species of palm nuts, macauba (Acrocomia aculeata) and the harder babaçu (Attalea speciosa). Most of the anvils were rock surfaces and had leftovers of only one palm nut species. The hammerstones used to process both palm nuts were not significantly different in weight, although the ones used for Ac. aculeata were longer. We found a higher frequency of nut-cracking sites in the drier lowland area of the park, reflecting differences in the density of the most common palm species, Ac. aculeata, and availability of raw stone material. The stone tool use observed in UNP is within the scope of previously reported in savannah capuchin populations. Our study widens the knowledge of stone tool-use diversity in wild capuchin monkeys, which could contribute to shaping conservation policy, including cultural traits.

Abstract BackgroundThe absence of a natural animal model is one of the main challenges to research in AD. AD‐type pathology has been described in chimpanzees and other primates’ brains. The bearded capuchin monkey (Sapajus libidinosus) is a New World primate that attracted attention mainly due to its skill in creating and using tools. We evaluated the brains of three captive capuchins (9, 29 and 33 years‐old) who died from natural causes at the Primate Center of University of Brasilia.MethodWhole brain was fixed in 4% buffered paraformaldehyde within 12 hours of death for three weeks. Structural 7T MRI was acquired in one case before brain slicing. Consecutive coronal sections from the fixed brain were embedded in paraffin, and 5um sections from paraffin blocks were used for staining and immunohistochemistry evaluation. All brain sections were stained with hematoxylin and eosin. Immunohistochemistry with β‐amyloid (4G8), phosphorylated tau (AT8), p62, TDP‐43, α‐synuclein (81A), 68 kDa neurofilament (2F11), GFAP and CD68 antibodies were performed in selected sections to analyze the following areas: frontal cortex, temporal cortex, parietal cortex, occipital cortex, anterior cingulate cortex, hippocampus, amygdala, basal ganglia, thalamus, mesencephalon, pons, medulla oblongata, and cerebellum.ResultMacroscopic evaluation of the brains showed considerable cortical gyrification. In addition, thick cortical ribbon was observed in the MRI. A complete neuropathological evaluation was available for two cases. Widespread β‐amyloid immunoreactivity was observed in the form of diffuse deposits, core‐space‐corona plaques, perivascular plaques, and amyloid angiopathy. A high frequency of classic neuritic plaques was observed. P‐tau antibody failed to label the dystrophic neurites. However, these lesions were revealed with p62 and neurofilament antibodies. Astrocyte hypertrophy surrounding plaques was observed without microglial activation. Very few hyperphosphorylated tau aggregates resembling neurofibrillary tangles and neuropil threads were found in the temporal and frontal cortex, and Lewy‐type and TDP‐43 pathology were not observed.ConclusionIn summary, we found β‐amyloid immunoreactivity, classic neuritic plaques surrounded by astrocyte hypertrophy, but only rare P‐tau aggregates. To our knowledge, this is the first evidence reporting brain AD‐like alterations in capuchin monkeys which suggest that this species can be considered an advantageous animal model for AD research.

Socioecological models predict that disputes between primate groups will be more intense than those within groups, given that the systematic loss of contests over a given resource will restrict the access of all of the members of that group to that resource. Higher levels of aggression are also expected for provisioned resources that have a more lucrative cost:benefit ratio. The levels of aggression in and between two free-ranging tufted capuchin monkey (Sapajus libidinosus) groups in the context of daily provisioning with bananas were evaluated. The aim of a complementary analysis was to identify possible predictors of the frequency of disputes at the site of the provisioned resource. The disputes were recorded using all-events sampling, while the social behaviour of the study groups was recorded by instantaneous scan sampling. The data were analysed using t-test, Mann-Whitney's U, and generalised linear modelling. Between-group disputes were no more intense than within-group events, and did not involve more individuals, or more adult females. The frequency of disputes increased as the number of individuals eating bananas increased. No evidence was found that disputes between groups were any more intense than those within groups. Dominance patterns may have affected these findings, by mediating intergroup disputes. An increase in the number of competitors affected the frequency of disputes at the site of the provisioned resource.

The Coexistence of People and Bearded Capuchins (Sapajus libidinosus) in a Nonindustrial Ecosystem: An Assessment of Tourist and Local Perceptions in the Coastal Area of Maranhão, Brazil

Background: It is well established that infection patterns in nature can be driven by host, vector, and symbiont communities. One of the first stages in understanding how these complex systems have influenced the incidence of vector-borne diseases is to recognize what are the major vertebrate (i.e., hosts) and invertebrate (i.e., vectors) host species that propagate those microbes. Such identification opens the possibility to identify such essential species to develop targeted preventive efforts. Methods: The goal of this study, which relies on a compilation of a global database based on published literature, is to identify relevant host species in the global transmission of mosquito-borne flaviviruses, such as West Nile virus, St. Louis virus, Dengue virus, and Zika virus, which pose a concern to animal and public health. Results: The analysis of the resulting database involving 1174 vertebrate host species and 46 reported vector species allowed us to establish association networks between these species. Three host species (Mus musculus, Sapajus flavius, Sapajus libidinosus, etc.) have a much larger centrality values, suggesting that they play a key role in flavivirus community interactions. Conclusion: The methods used and the species detected as relevant in the network provide new knowledge and consistency that could aid health officials in rethinking prevention and control strategies with a focus on viral communities and their interactions. Other infectious diseases that harm animal and human health could benefit from such network techniques.

Comparative anatomy the basis for studies of evolution, and radiographic and tomographic aspects, as auxiliary methods in the investigation of anatomical particularities, reinforce evolutionary research. Therefore, the aim of this study was to describe the vertebrae, sternum, and ribs of the capuchin monkey (Sapajus libidinosus) by means of anatomical dissection and radiographic and tomographic images. To this purpose, four cadavers were used in the anatomical analysis and five living animals for the imaging exams. The bones were described and compared with data from other primates species found in literature. Student's t-test for independent samples was performed. The vertebral column of the comprises seven cervical, 13 or 14 thoracic, five or six lumbar, two or three sacral, and 23 or 24 caudal vertebrae. The atlas is characterized by three foramina on the wing. The seventh cervical vertebra had a transverse foramen in one specimen. The anticlinal vertebra is always the penultimate thoracic one, the ninth pair of ribs is always the last sternal pair, and the last two are buoyant. The sternal was composed of five or six sternebrae. The lumbar vertebrae showed a bifurcated spinous process. Three different sacral morphologies were observed. The structures identified macroscopically could be well determined through radiographic and tomographic images. S. libidinosus presented anatomical characteristics more similar to those of man and of platirrinos monkeys. The knowledge obtained by macroscopic anatomy and tomographic and radiological exams contributes significantly to comparative evolutionary studies.

The development of expertise at cracking palm nuts by wild bearded capuchin monkeys, Sapajus libidinosus

ABSTRACT: Sapajus libidinosus is a New World primate belonging to the Cebidae family that lives in the caatinga and cerrado, which are known Brazilian biomes. It is currently classified as near threatened, almost endangered, by the main animal protection organizations. Knowledge of biochemistry, the C-reactive protein, and the proteinogram are important for the preservation of this species. Our study established reference intervals for several biochemical variables and the proteinogram. For this purpose, blood samples were collected from 50 S. libidinosus monkeys (25 males and 25 females) kept in captivity at the Brazilian state of Paraíba. Descriptive analysis and reference intervals were estimated following the guidelines of the American Society of Veterinary Clinical Pathology, using the Reference Value Advisor 2.1 software. In the overall population (n=50), significant differences (P < 0.05) were noted for creatinine and total proteins when considering the age factor (higher in adults), as well as for albumin and indirect bilirubin (higher in juveniles). Sex-associated differences (females versus males, P < 0.05) were reported for serum urea and creatinine (higher in males), as well as for albumin and Beta-Globulins (higher in females). In conclusion, to the authors’ best knowledge, the present results are innovative and can be used as reference intervals for assessing the animals’ health status. Moreover, it is also pioneer in determining the C-reactive protein in this species. It is important to emphasize that gender and age categories can have an influence and should be considered when interpreting the tests results.

Masturbation is part of the natural behavioral repertoire of primates, with visual sexual stimuli known to trigger this behavior. Here, we report masturbation events triggered by visual sexual stimulus (VSS) in the South American primate Sapajus libidinosus. We observed a multi-male multi-female captive colony of 17 bearded capuchins between January and October 2014. Over this period, we registered 11 copulation events, 68 attempt copulations, and five masturbation events. The same low-ranking male (named Fu) performed all masturbation events. Fu directly looked at other individuals engaged in sexual displays while he masturbated in three events. The masturbation events associated with VSS lasted up to 2min and 40s. Our observations show that VSS can trigger masturbation in capuchin monkeys. The low hierarchy rank of the male, and the consequent lack of mating opportunities in the multi-male multi-female recently formed group in captivity, may have prompted the masturbation events.

There are strong physiological and behavioral differences that allow animals to live in forests versus savannas. For example, terrestrial forest-dwelling mammals tend to be small compared to species living in savannas. Robust capuchin monkeys (genus Sapajus) are widespread in tropical South America, occurring in both forest and savanna environments, with forest species considered basal in an evolutionary context. Whether or not skull shape and size variations are associated with variation in resource use remains unknown, particularly for the two species living in savanna (Sapajuslibidinosus and S. cay). Here we show that savanna species present convergent size and skull characteristics that may facilitate living in this new environment. Geometric morphometric methods were used to assess skull size and shape variation for 184 Sapajus specimens distributed across South America. We used phylogenetic generalized least squares to test size against environmental variables and multivariate morphological trajectories/partial least square analyses on the skull shape to detect shape differences in specimens between forest and savanna biomes. Our findings reveal Sapajus size reduction in the evolutionary transition from forest to savanna, a process related to increasing seasonality. Moreover, we found morphological parallelism in the skull (e.g., muzzle shortening) and (large) molars in the two savanna species, features that may facilitate the processing of harder food such as fallback resources. We associate these phenotypic differences to the evolutionary process of colonizing the savannas by primates (including early hominins), leading to morphological adaptations to tolerate stressful, seasonal environments, such as body size reduction and ingestion and mastication of tough foods.

Macroscopic bone analysis and evaluation through imaging methods are essential in the recognition of natural and altered structures. Therefore, this study aimed at describing the osteology the thoracic limb of Sapajus libidinosus in bone pieces, identifying them in radiographic and tomographic images. For this, four cadavers were used in the macroscopic analysis and five animals for the imaging exams, of which four were euthanized and added to the macroscopic stage. For imaging exams, the animals were kept anesthetized. All bones were documented, structures described, and compared with literature data from human and nonhuman primates. There was no statistical difference between males and females regarding the length of the forelimb bones. Most of the bone structures of the scapula were well identified in the imaging methods, being more restricted in the ventrodorsal projection. The clavicle presented very limited visualization. The humerus, as well as the radius and ulna, were not well portrayed in their proximal and distal epiphyses by radiography. However, they were well identified on tomography. All structures described in the macroscopic image of the carpal and metacarpal bones could be identified through radiography and tomography, and the radiographic examination of this region is an excellent method for identifying fractures. The glenoid notch of the scapula was not visualized by any imaging method. S. libidinosus presented anatomical characteristics more similar to those of neotropical primates and man, being a great indicator of an experimental model for studies in these species.

Vertebrate predation was a vital behavior during human evolution. Some Afro-Eurasian primates, such as baboons (Papio spp.) and chimpanzees (Pan troglodytes), frequently hunt and consume vertebrate prey. Capuchin monkeys (Cebus and Sapajus) are omnivorous platyrrhines, and also hunt and consume vertebrates opportunistically. Bearded capuchin monkeys (Sapajus libidinosus) living in semi-arid savannah environments use stone tools to obtain food resources. However, only one population at Serra da Capivara National Park, Brazil, is known to use stick probes to enhance predation. I present data collected for 2 years on vertebrate predation and consumption by two groups of capuchins in this population. Recording vertebrate predation events ad libitum, I observed 72 events, at a rate of 4.6 events/100 h. The most frequent prey were lizards and snakes, followed by birds and rodents, including larger rodents such as adult rock cavies (Kerodon rupestris). The monkeys also preyed on bats, albeit rarely. Predation on vertebrates, including prey that are large relative to their body size, use of tools to aid predation, and a high degree of terrestriality in the savannah environment make robust capuchins a suitable model to understand human evolution, as well as a good comparison with Afro-Eurasian primate models.