Despite recent advances pushing back the earliest record of tool use, how and when it first emerged in hominins, and the extent to which it featured amongst the numerous co-existing species, remain critical questions in paleoanthropology. In addition to analyzing fossils and lithic toolkits, novel strides in understanding this might be made by studying the skeletons of the great apes, as well as more distantly related tool-using primates and applying resultant findings to the fossil record via predictive modelling. We review current methods of extrapolating tool-use capabilities in extinct and extant taxa and provide an innovative methodological framework to analyze osteological remains for evidence of percussive tool use, using chimpanzees as a case study. We propose a shift in current methodological practice, wherein both sides of the body, rather than just one, should be routinely scanned to understand of the effect percussive tool use on primate bone. Key species, including long-tailed macaques (Macaca fascicularis ssp.), capuchins (Sapajus and Cebus sp.) and chimpanzees (Pan troglodytes ssp.), all of whom engage in lithic percussion, should be the work's focus. Due to bone's dynamic ability to respond to mechanical strain, percussive forms of tool use, like nut-cracking, could cause morphological changes in the dominant hands of tool users as compared to their non-dominant hand, or the hands of primates who do not engage in percussive behaviors. However, this potential "damage signature" has not been quantified. Thus, we propose a methodology for examining the effect of percussive tool use on primate bone by scanning skeletal remains bilaterally, analyzing directional asymmetry, and using machine learning to discern patterns of variation. Long-term, our proposed methodology may be extrapolated to examine the lasting impact of tool use on the bones of extinct hominins.

Primates constitute an integral part of many African ecosystems. In some areas, primate species can be locally very abundant, while in others they are rare or absent. Our central question is: does the abundance of primate bones (or carcasses) reflect the abundance of local living populations? Past bone surveys in Amboseli National Park, Kenya, and Virunga National Park, Democratic Republic of Congo, revealed a positive correlation between carcass abundance and living mammal communities, with a notable exception: a low abundance or absence of primate carcasses when compared to other medium-sized and large mammals. Recent research conducted at Gorongosa National Park, Mozambique, revealed a similar discrepancy between the abundance of primate carcasses and mammalian live census data. This study aims to understand this mismatch between live and dead by examining the influence of ecological factors on primate carcass occurrence and bone distribution in the modern rift ecosystem of Gorongosa National Park. To address these issues, we investigated whether (1) landscape type, proximity to roads, and water sources (pans, rivers, and lakes) predict primate carcass occurrence relative to other mammal taxa, and (2) the accumulation of primate bones significantly differs from that of other mammals in annually flooding and non-annually flooding landscapes (broadly speaking, in the floodplain vs. higher areas). We analysed 26 bones from 18 chacma baboon individuals (Papio ursinus) and 255 bones from 20 other mammal species. Generalised Linear Model (GLM) outputs suggest that permanent water sources such as rivers and lakes are key drivers of primate bone accumulation (p < 0.05). A Fisher’s Exact Test indicates that primate bones are deposited more frequently in Rift Valley Riverine Floodplain landscapes (p < 0.05). Given that baboons regularly cross rivers in Gorongosa, these findings also suggest that crocodile predation may play an important role in determining where baboon carcasses ultimately accumulate, potentially contributing to the observed mismatch between living and dead communities. These findings have important implications for our understanding of primate bone accumulations in the African fossil record, where some palaeontological sites contain abundant primate fossils whereas others preserve few or none.

The distribution of African great apes has remained unconfirmed regarding their southern limit, particularly on the western side of the continent. IUCN maps include the Mayombe forest of Angola as part of the estimated distribution of western lowland gorillas (Gorilla gorilla gorilla) and central chimpanzees (Pan troglodytes troglodytes). However, until now, there were no records confirming the continued presence of both species. The Mayombe forest is a key biodiversity hotspot and a potentially important stronghold for the conservation of great ape populations in Africa. Here, we report the first systematic evidence of both species in the Mayombe National Park, Cabinda, Angola. In 2023, a grid of camera traps was systematically deployed, producing the first visual records of gorillas and chimpanzees. Building on these findings, in 2024, a pilot survey including ad libitum field observations was carried out along exploratory trails to maximise data collection. The combination of these records identified a hotspot of great ape activity where six transects were established, and systematic direct and indirect evidence was documented. Chimpanzees were recorded more times across a broader range of evidence categories, while gorillas appeared less and seemed more spatially restricted. Notably, both species were detected at overlapping sites but never simultaneously, indicating sympatric coexistence with spatio-temporal partitioning. These findings confirm the southernmost predicted distribution of both species for this part of Africa, filling critical gaps in the understanding of great ape evolution and biogeography, and providing a baseline for the first demographic and ecological census of great apes in Angola.

What do we know about how the most abundant species of primates in Gorongosa National Park (Mozambique) exploit a highly seasonal and heterogeneous environment? This review examines current knowledge and key gaps in our understanding of Gorongosa’s vegetation in relation to the diet and feeding ecology of grey-footed chacma baboons (Papio ursinus griseipes). By synthesising existing literature of Gorongosa’s historical context, seasonality, landscape structure, and plant communities, this review provides environmental context for understanding baboon feeding ecology. Baboons appear to be among the most numerous mammals in Gorongosa National Park, inhabiting diverse landscapes and utilising the environment dynamically. Gorongosa National Park provides a useful contemporary system for investigating wild living primates, as it is a highly seasonal area with mosaic environments and a complex history, and it offers a valuable ecological analogue for early hominin environments. In this review, previous work on Gorongosa’s chacma baboon ecology and diet is synthesized, highlighting their pronounced dietary flexibility, foraging strategies, and extensive resource use. We also briefly consider their possible ecological role in seed dispersal, vegetation dynamics, and interactions with invasive plants, as these aspects are poorly documented in the park. Overall, this work organises existing data on baboon feeding ecology in Gorongosa, identifies key gaps, and outlines priorities for future integrative research, contributing to broader discussions of primate ecology, conservation, and human evolutionary models.

The co-occurrence of species within the same area raises fundamental questions about how they can persist while sharing space and resources. One of the central aims of community ecology is to understand the processes that allow species to coexist over time. The sympatry between primates and ungulates has not received much specialized attention, despite long-term acknowledgment that the two groups frequently co-occur. In this contribution, we have reviewed and summarized empirical evidence from a set of published studies to determine the nature of primate and ungulate association in space and time, the ecological contexts within which such associations occur, and the types of interactions that have been reported. We particularly examined the trends in the study taxa, the geographic distribution of research, and the functional categories of interactions. Within the literature, interspecific interactions are frequently reported in Africa, between baboons (Papio sp.) and small to medium-sized ungulates. Foraging facilitation and antipredator benefits are among the most frequently documented interaction types, typically resulting in commensalistic or asymmetrical mutualistic outcomes favouring ungulate species. Nonetheless, mutualism and antagonistic interactions are also reported, which indicates the context-dependent nature of these relationships. The frequency and form of associations appear to further depend on seasonal variation and habitat structure, although these factors were not consistently taken into account in the studies considered in this review. This synthesis helps establish a set of research priorities to promote more systematic and focused studies of primate-ungulate sympatry.

The consumption of small vertebrates occurs to varying degrees among many non-human primates. This dietary element may have constituted an important source of nutrition for early hominins, particularly during periods of food scarcity, providing a stepping stone to the exploitation of larger animals. Capuchin monkeys regularly consume small vertebrates across their range. Expanding our knowledge of the contribution of animal matter to these primates’ diets can shed light on the proximate and ultimate drivers of small vertebrate consumption across primate taxa, including humans. We report on the most extensive record of bearded capuchin ( Sapajus libidinosus ) vertebrate predation so far available: 45 months of observations of vertebrate predation in two sympatric groups in Fazenda Boa Vista, in northeastern Brazil. We estimated the effect of provisioning, sex, age class, fruit and insect availability, rainfall, humidity, and temperature on predation rates using a zero-inflated negative binomial algorithm with random effects. We found mammal and saurian consumption is habitual in this population of S. libidinosus . Prey brains and viscera tend to be accessed before the rest of the body. Predation rates were higher in males compared to females and in adults compared to infants across groups. Our results also identified small vertebrates as key energy sources for bearded capuchins under decreased fruit availability and show that provisioning reduces predation rates. Future work should assess small vertebrate predation as a possible stepping stone in the emergence of human exploitation of large animals by re-analyzing fossil faunal assemblages for evidence of small vertebrate predation.

The timing of divergence between hominins and the bonobo-chimpanzee clade has been at the core of palaeoanthropological debate for over a century. The earliest molecular studies indicated divergence times ranging from 5 Ma to as recently as 1.3 Ma. This study critically reviews the trends of time estimates published between 1967 and 2023, and analyses how these are supported or rejected by the current molecular and fossil records. We compiled 202 divergence estimates and defined three distinct thresholds based on fossil evidence at 4.4 Ma (Australopithecus anamensis and Ardipithecus ramidus), 6.2 Ma (Orrorin tugenensis and Ardipithecus kadabba), and 7.2 Ma (Sahelanthropus tchadensis). We then used these thresholds to filter out molecular estimates that are too young to fit the fossil record. Overall, the data suggests a divergence event within the late Miocene, with each threshold pushing it further back, 8.63–6.38, 10.33–7.81, and 10.95–8.81 Ma, respectively. We use a quadratic regression to demonstrate that estimates have been slowly shifting from 6 Ma to 8.5 Ma over the past 56 years. A Bayesian meta-analysis of genomic estimates filtered by our most consensual threshold (i.e., assuming Australopithecus belongs to Hominini) indicates that the split must have occurred early in the late Miocene, most likely before 7 Ma ( 99.5

"Terrestrial" primates are not common nor well defined across the order. In those species that do use the ground, terrestriality is rarely documented outside daylight hours. Predation risk is thought to have shaped conserved behaviors like primates' selection of arboreal sleep sites, but it is less clear-particularly at the landscape scale-how predation risk interacts with other ecological and seasonal variables to drive terrestriality. This camera trapping study investigates patterns in terrestrial behavior both spatially and temporally across neighboring populations of chacma baboons. We use camera trap data from two terrestrial grids, one established within and one outside the boundaries of Gorongosa National Park, Mozambique. We model how baboon terrestrial activity varies with woody cover, proximity to water, season, anthropogenic variables, as well as predation risk. We also model how terrestrial activity varies across the diel cycle and use overlap analyses to explore differences in the baboon populations' activity patterns. We find no significant predictors of geospatial variation in the terrestrial activity of baboons across each grid but do find evidence of higher terrestrial activity in the late dry season. We also find significantly different diel patterns of baboon activity detected across each grid. Baboons likely use the ground more in the dry season for accessing water and resources when arboreal foods are less abundant. Diel variation between the two populations suggests that baboons might utilize the ground more during "riskier" crepuscular and nocturnal hours where leopards are not present.

IntroductionRoute-based navigation is a common movement strategy for a variety of taxa, wherein animals repeatedly re-use familiar paths during travel. However, this type of navigation is understudied in wild animals that experience regular displacement, raising questions about the robustness and longevity of such routes and route memories. The seasonal flooding of Gorongosa National Park, Mozambique, provides an opportunity to test multiple facets of route-based navigation in wild primates, due to its high seasonality and annual flooding.MethodsData was collected from GPS collars placed on four chacma baboons in two troops in Gorongosa National Park. Using GPS points taken every 15 minutes, we use nearest-neighbour analysis to compare daily paths across the year, to identify high-use paths. We then look at the identified high-use paths to see if they are used across the entire study period, with a focus on areas that were vacated for more than two months of the study period.ResultsWe find that the baboons do have vacated areas, but return to the same areas after displacement. We did not find high-use routes in these areas used both before and after displacement, although high-use routes did exist that were used across the study period in different areas.DiscussionOur results indicate that routes may not be maintained in long-term memory spanning several months, or that route reuse is in part dependant on seasonal resources or navigational aids. Although the study period did not span a full year, this study presents a replicable method of analysing route reuse and identifying high-use routes without traditional methods of manually overlaying and analysing daily paths.

OBJECTIVES:This research aimed to understand how sleep site selection compared to other study sites in baboons living in a low-predator density, highly seasonal environment. We compared baboon troops in two distinct habitat types with different seasonal influences within the park, one that flooded annually and one that did not. We compared their sleep site use, reuse, and location relative to home range boundaries and areas of interest (AOIs) with each other and baboons in other areas to understand whether season, habitat familiarity, or position in the home range influenced sleep site choice. METHODS:Using GPS collar data taken at 15-min intervals from four gray-footed chacma baboons (Papio ursinus griseipes) in Gorongosa National Park, Mozambique, we established the location of sleep sites, home range boundaries, and AOIs, or places where the baboons repeatedly stopped for more than 15 min. Study subjects ranged either in dense woodland or in a seasonally flooded alluvial floodplain. We used a linear mixed-effects model to predict sleep site reuse based on distance to the habitat edge and AOIs, and Wilcoxon signed-rank tests to determine if morning or evening AOIs influenced sleep site location. We counted the number of reuses of each sleep site before and after the flooding period and compared this data to data in other baboon study sites. RESULTS:We found that, as in other study sites with less seasonality and higher predation risk, baboons in Gorongosa change sleep site frequently and utilize multiple sleep sites throughout their home range, although they more often use sleep sites closer to the center of their home ranges. However, unlike other studies, we found that the location of the last AOI of the day more strongly predicted sleep site location than the first AOI of the next day in one troop, with baboons traveling further from their sleep site to their first AOI in the morning than from their last evening AOI to the sleep site. CONCLUSIONS:Despite high seasonality and low predator density, baboons in Gorongosa National Park changed sleep sites frequently, as do other studied baboon troops in areas with high nocturnal predation rates. In addition, their propensity to sleep closer to the last AOI of the day may imply that they plan their daily paths toward their chosen sleep site, or that they sleep opportunistically at the end of the day. This study provides a baseline of behavioral data for comparison to other sites and future work in Gorongosa, where predator density continues to rise since the time of the study.

OBJECTIVES:With contemporary, human-induced climate change at a crisis point, extreme weather events (e.g., cyclones, heatwaves, floods) are becoming more frequent, intense, and difficult to predict. These events can wreak rapid and significant changes on ecosystems; thus, it is imperative to understand how wildlife communities respond to these disruptions. Primates are perceived as being a largely adaptable order, but we often lack the quantitative data to rigorously assess how they are impacted by extreme environmental change. Leveraging detections from a long-term camera trap survey, this opportunistic study reports the effects of an extreme weather event on a little-studied population of free-ranging primates in Gorongosa National Park, Mozambique. MATERIALS AND METHODS:We examined shifts in gray-footed chacma baboon (Papio ursinus griseipes) and vervet monkey (Chlorocebus pygerythrus) spatial distribution and relative abundance following Cyclone Idai-a category four tropical cyclone that struck Mozambique in March 2019. RESULTS:Baboon spatial distributions were impacted in the first month after the cyclone, with more detections in areas where flooding was less severe. Spatial distributions renormalized once floodwaters began to recede. We describe vervet monkey spatial distribution trends, though sample size limitations inhibited statistical analysis. Primate relative abundance did not appear to substantially decrease following the cyclone, suggesting troops were able to adopt behavioral adjustments to evade rising floodwaters. DISCUSSION:These findings highlight the behavioral flexibility of Gorongosa's primates and their ability to adapt to extreme-if temporary-disruptions, with implications for primate conservation in the Anthropocene and research into how rapid climatic events may have shaped primate evolution.

OBJECTIVES:Baboons possess sophisticated physical and social cognitive abilities; hence, the lack of evidence to date of large-scale behavioral variation in these primates is puzzling. Here we studied a candidate for such variation-the stripping of bark from Acacia robusta trees for consumption of the sap and soft tissue underneath-in Gorongosa National Park, Mozambique. MATERIALS AND METHODS:We surveyed an area inhabited by ~60 troops of chacma baboons, recording the availability and characteristics of the target trees, as well as the presence or absence of bark-stripping at 45 habitat plots distributed across a grid covering an area of ~300 km2. RESULTS:Camera traps confirmed the presence of baboons at all habitat plots, and we identified regional clumping in the distribution of the behavior, a pattern consistent across two consecutive years. Proportion and mean height/width of A. robusta did not predict whether bark-stripping behavior was present at a given site, nor did broader ecological variables such as habitat type and distance to the nearest water source. However, stripping sites had significantly higher numbers of A. robusta than non-stripping sites, and within a given bark-stripping site, baboons preferred to strip taller and wider trees among those available. DISCUSSION:The prominent geographical clustering we uncovered may have been driven by opportunity (i.e., the prevalence of A. robusta at a given site), but is also consistent with a possible (non-mutually exclusive) cultural interpretation. We propose avenues for future research on Gorongosa's baboons to better quantify the relative contributions of ecology, genetics, and social learning to the prevalence of bark stripping. We also briefly consider the potential relevance of baboon bark stripping to elucidating early hominin foraging strategies.

We know vanishingly little about how long-lived apes experience senescence in the wild, particularly with respect to their foraging behaviors. Chimpanzees use tools during foraging, and given the cognitive and physical challenges presented by tool use, tool-use behaviors are potentially at a heightened risk of senescence, though this has never been investigated in wild individuals. Accordingly, we sampled data from a longitudinal video archive that contained footage of wild chimpanzees using stone hammers and anvils to crack hard-shelled nuts (nut cracking) at an ‘outdoor laboratory’ over a 17-year period (with focal chimpanzees aging from approximately 39–44 to 56–61 years across this period). Over time, elderly chimpanzees began attending experimental nut-cracking sites less frequently than younger individuals. Several elderly chimpanzees exhibited reductions in efficiency across multiple stages of nut cracking, including taking longer to both select stone tools prior to use and use tools to crack open nuts and consume the associated pieces of kernel. Two chimpanzees began using less streamlined behavioral sequences to crack nuts, including a greater number of actions (such as more numerous hammer strikes). Notably, we report interindividual variability in the extent to which elderly chimpanzees’ tool-use behaviors changed during our sample period – ranging from small to profound reductions in engagement and efficiency – as well as differences in the specific aspects of nut cracking that changed for each individual. We discuss the possible causes of these changes – and recommendations for future research – with reference to literature surrounding the senescence of captive and wild primates.

Dispersal behavior influences gene flow and the spatial distribution of genetic diversity, which is crucial for a species' evolutionary trajectory and population persistence under environmental changes. We used gene flow as a proxy to investigate dispersal patterns in the grayfoot chacma baboon (Papio ursinus griseipes) in Gorongosa National Park (GNP), central Mozambique. The baboons inhabit a mosaic landscape with a seasonally variable environment. Thirty-two years ago, GNP was the epicenter of a major war that severely reduced apex predators, resulting in limited mammalian predation on baboons. We aimed to characterize genetic diversity, examine the extent and direction of sex-biased gene flow at different time frames and investigate changes in population size and recent migration events. We collected 121 non-invasive DNA samples and analyzed uni- and bi-parentally inherited markers, comprising mitochondrial DNA, autosomal and Y-linked microsatellites, at two geographic locations (GNP and Catapú Forest Reserve) 150 km apart. We observed high genetic diversity and no evidence of a recent population decline. We identified six mitochondrial haplotypes, including a genetically distinct one in Catapu Forest Reserve. We found molecular evidence for historical and current male-mediated gene flow and female philopatry. Our results highlight the resilience of dispersal patterns in Papio sp. in diverse and seasonally variable ecosystems which have been disturbed by anthropogenic activities.

This contribution is an introduction to and synthesis of the special issue of the AJBA on Primate Adaptations in a Highly Seasonal and Heterogeneous African Ecosystem. The eight research papers in this special issue provide the first compilation of primatological research to emerge from Gorongosa National Park and represent a major landmark in the development of primatology as a science in Mozambique. Primatological field studies in the park were initiated in 2016 under the umbrella of the Paleo-Primate Project Gorongosa with the aim of exploring the deep time evolutionary history of the Gorongosa ecosystem and establishing a long-term primatological field research program. This initiative has resulted in the training of a new generation of primatologists, including the first from Mozambique. The papers in this volume focus on the behavior, ecology, adaptations, and genomics of baboons and vervet monkeys, and set the stage for the study of other primates in Gorongosa, including samango monkeys and nocturnal strepsirrhines. The environmental characteristics of the Gorongosa ecosystem, with major rivers and lakes in a dynamic mosaic of forests, woodlands, wetlands, and grasslands, and rich biodiversity, make Gorongosa a suitable analog for the environments in which early hominins are thought to have evolved. This special issue is dedicated to the memory of our dear friend and colleague Dr. Marc Stalmans, who was the Director of Science of Gorongosa National Park from 2012 to 2025.

OBJECTIVES:Studying object manipulation may offer insights about the emergence of habitual tool use in the hominin clade. Previous research on object manipulation has focused on habitual tool-using animals such as apes, capuchins, dolphins, and corvids. Investigating object manipulation in wild baboons, a highly social, ecologically adaptable, and terrestrial primate that is not a habitual tool user, can shed further light on the pressures favoring or inhibiting the use of technology. In this study, we investigate factors that influence object manipulation in the chacma baboons of Gorongosa National Park, across demographic and environmental conditions. MATERIALS AND METHODS:We collected data using focal and scan sampling, with the aid of the Animal Observer app, and recorded object use and other behaviors. We followed three focal troops: Chitengo, Montebelo, and Floodplain. A total of 2262 observations were recorded across 88 individuals (787 events involved object use). RESULTS:Mixed-effects logistic regressions revealed that habitat, age, and substrate use significantly predicted object use among baboons. Object use was most likely in open forests. Adults are less likely to engage in object manipulation, and this behavior decreases with age, which is in line with previous results reported for bonobos. Interestingly, baboons spend more time manipulating objects arboreally than terrestrially. DISCUSSION:Our findings contribute to the current discussions about the contexts that promote tool use across the primate order. Further studies expanding on these results and assessing differential availability of resources can provide a more comprehensive understanding of the evolution of tool use.

Physical evidence of early hominin perishable tools is scarce. However, it is reasonable to assume the mechanical constraints surrounding tool use and manufacture have remained somewhat constant. Using a functional framework to understand the technical capabilities of extant hominoid tool users presents a novel approach to predict the perishable tool-using capabilities of our earliest relatives. We investigated the structural and mechanical properties of plant materials used by wild chimpanzees to make termite fishing probes. Materials sourced from plant species extensively used by chimpanzees produced implements of greater flexibility than those constructed from plants never selected by chimpanzees. This pattern was also reflected in chimpanzee tool species preferences, with preferred plant species producing highly flexible implements. Implement flexibility aligns with functional predictions and likely facilitates termite attachment. Our findings provide insights into the technical skills associated with perishable artefact-making and raise questions about how this knowledge is learnt and culturally transmitted.