Portrait of Professor Tracy Kivell

Professor Tracy Kivell

Professor of Biological Anthropology
Head of School
Director of the Animal Postcranial Evolution (APE) Lab

About

Professor Tracy Kivell is a palaeoanthropologist who studies the evolution of the postcranial skeleton in living and fossil primates, including our human ancestors (hominins). Her research focuses on the functional morphology of the hand in fossil apes and hominins to further our understanding of the origin of human bipedalism, tool use and manipulation throughout our evolutionary history. Tracy aims to better understand the relationship between bone shape and function through analyses of ontogeny (development), internal (trabecular and cortical) bone structure, and the biomechanics of primate locomotion. 

Professor Kivell received her PhD in 2007 from the University of Toronto, working on the developmental morphology of the ape wrist and the origin of human bipedalism. Before coming to the University of Kent, she was a Research Associate, teaching human gross anatomy at Duke University, USA (2007-2009), and was postdoctoral Junior Researcher in the Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Germany (2009-2013). Tracy has participated in palaeontological field excavations at Miocene sites in Hungary as well as Plio-Pleistocene sites in South Africa. 

Research interests

Professor Tracy Kivell’s current research interests include:

  • functional morphology of the primate postcranial skeleton 
  • internal (trabecular and cortical) bone structure in extant and fossil primate hands to better understand the evolution of locomotion and manipulation in hominins 
  • biomechanical analyses of terrestrial and arboreal locomotion in apes
  • functional morphology of fossil hand bones of Miocene hominoids.

Projects in which she is involved include the following:

  • NEWHUMAN Pathways to humanity: adaptive niche diversity at the origins of the human lineage (PI: Matthew Skinner, Senior Staff Member: Tracy Kivell; funded by European Research Council Consolidator Grant 2019-2024)
  • GRASP  Evolution of the human hand: Grasping trees and tools (PI: Tracy Kivell; funded by European Research Council Starting Grant 2014-2019)
  • Director of research on Australopithecus sediba and Homo naledi hand fossils: investigation of Au. sediba and H. naledi hand remains from South Africa in collaboration with, among others, Lee Berger (University of the Witwatersrand), Matthew Tocheri (Lakehead University), Caley Orr (University of Colorado), and Steve Churchill (Duke University). 
  • Fossil hominin and hominoid hand use: comparative investigation of fossil hominin (australopiths to Neanderthals) and Miocene hominoid hand remains using morphometric and micro-CT data. This research aims to shed light on locomotor and tool-use behaviours throughout the evolution of the human lineage. Collaborators include: Matthew Skinner (Kent), Matthew Tocheri (Lakehead University), Erin-Marie Williams-Hatala (Chatham University), Steve Churchill (Duke University), Antonio Rosas (MNCN, Madrid) and David Begun (University of Toronto). 
  • Functional signals in trabecular and cortical bone structure: a comparative investigation of internal bony morphology of the primate hand and other regions of the postcranial skeleton to assess variation in joint loading patterns and how this reflects differences in locomotor and manipulative behaviours. Collaborators include: Matthew Skinner (Kent), Dieter Pahr and Alex Synek (Vienna University of Technology), Jean-Jacques Hublin (Max Planck Institute for Evolutionary Anthropology).
  • Biomechanics of primate locomotion: investigation of variation in biomechanics of terrestrial and arboreal locomotion in apes as well as other primates, including the aye aye, in both captive and natural settings. Collaborators include: Daniel Schmitt (Duke University) and Roshna Wunderlich (James Madison University).

Teaching

Professor Kivell teaches on the following modules:

Undergraduate

  • SE302: Foundations in Biological Anthropology
  • SE541: Palaeoanthropology

Postgraduate

  • SE8013: Skeletal Functional Morphology (starting September 2019)

Supervision

Professor Kivell can offer supervision of PhD and MA/MSc research within any of her areas of interest – functional morphology of the postcranial skeleton, including external and internal (using microCT data) bony morphology and primate locomotor behaviour, with a particular focus on the upper limb.

Postdoctoral researchers

  • Dr Julia Arias-Martorell (Maria Sklodowska-Curie Fellow)
  • Dr Ameline Bardo (Fyssen Foundation Fellow) 
  • Dr Alastair Key (British Academy Fellow) 
  • Dr Szu-Ching Lu (ERC Postdoctoral Researcher, 2015-18) 
  • Dr Diana Samuel (ERC Postdoctoral Researcher, 2014-16) 

Current PhD students

  • Simon Chapple: Assessing the variability and complexity of occlusal tooth patterning in primate enamel-dentine junction morphology as it relates to current systems of tooth crown nomenclature (co-supervisor)
  • Kim Deckers: Ontogenetic changes in internal bone structure: a study of the primate upper limb with implications for the evolution of human locomotion and manipulation (primary supervisor)
  • Chris DunmoreSkeletal form and function of the primate hand (co-supervisor)
  • Leoni GeorgiouLocomotor signals in the trabecular structure of the femur in extant and extinct hominoids (co-supervisor) 
  • Emma Bird: It’s all in the wrist: understanding the evolution of Homo tool-making through internal bone structure (primary supervisor)
  • Victoria Lockwood: Pressure and kinematics of the human hand during arboreal locomotion and tool behaviours (George Washington University, USA) (co-supervisor) 

Past PhD students

  • Johanna Neufuss (PhD in 2017)Hand use and posture during locomotor and non-locomotor behaviours in wild, habituated gorillas, chimpanzees and bonobos
  • Zewdi Tsegai (PhD in 2018): Systemic and functional patterns of human and chimpanzee internal bone structure: a regional, systemic and ontogenetic approach (Max Planck Institute for Evolutionary Anthropology) 
  • Nicholas Stephens (PhD in 2018): Functional morphology of the hand: Detecting behaviour during life by way of variation in internal trabecular architecture (Max Planck Institute for Evolutionary Anthropology) 

Past Masters' students

  • Victoria Lockwood (2017-18): Biomechanics of the human hand during suspensory arboreal locomotion: a combined pressure and kinematic approach
  • Ann-Marie Schilling (2011-2012)Trabecular bone structure in the primate wrist

Professional

  • Research Associate, Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology (Leipzig, Germany) 2013-present. 
  • Soapbox Science Canterbury, co-organiser of the first Soapbox Science events in Kent, sharing the research of women scientists with the public. 
  • Biological Anthropology Women’s Mentoring Network (BAWMN), Steering Committee since 2010, Chair in 2011-12.

Professor Tracy Kivell strongly supports the public understanding of science, and particularly the promotion of women in science. She has done radio and/or television interviews for the BBC, NPR and CBC’s Quirks and Quarks, and Daily Planet, including BBC4’s 'Dissected: The Incredible Human Hand and Foot'. She is available to provide academic comment on topics related to the evolution of human tool use and locomotion, primate manipulative abilities, or functional morphology in the human or primate skeleton more broadly. 

Publications

Showing 50 of 87 total publications in the Kent Academic Repository. View all publications.

Article

  • Dunmore, C., Skinner, M., Bardo, A., Berger, L., Hublin, J., Pahr, D., Rosas, A., Stephens, N. and Kivell, T. (2020). The position of Australopithecus sediba within fossil hominin hand use diversity. Nature Ecology and Evolution [Online]. Available at: https://dx.doi.org/10.1038/s41559-020-1207-5.
    The human lineage is marked by a transition in hand use, from locomotion towards increasingly dexterous manipulation, concomitant with bipedalism. The forceful precision grips used by modern humans probably evolved in the context of tool manufacture and use, but when and how many times hominin hands became principally manipulative remains unresolved. We analyse metacarpal trabecular and cortical bone, which provide insight into behaviour during an individual’s life, to demonstrate previously unrecognized diversity in hominin hand use. The metacarpals of the palm in Australopithecus sediba have trabecular morphology most like orangutans and consistent with locomotor power-grasping with the fingers, while that of the thumb is consistent with human-like manipulation. This internal morphology is the first record of behaviour consistent with a hominin that used its hand for both arboreal locomotion and human-like manipulation. This hand use is distinct from other fossil hominins in this study, including A. afarensis and A. africanus.
  • Georgiou, L., Dunmore, C., Bardo, A., Buck, L., Hublin, J., Pahr, D., Stratford, D., Synek, A., Kivell, T. and Skinner, M. (2020). Evidence for habitual climbing in a Pleistocene hominin in South Africa. Proceedings of the National Academy of Sciences of the United States of America [Online] 117:8416-8423. Available at: https://doi.org/10.1073/pnas.1914481117.
    Bipedalism is a defining trait of the hominin lineage, associated with a transition from a more arboreal to a more terrestrial environment. While there is debate about when modern human-like bipedalism first appeared in hominins, all known South African hominins show morphological adaptations to bipedalism, suggesting that this was their predominant mode of locomotion. Here we present evidence that hominins preserved in the Sterkfontein Caves practiced two different locomotor repertoires. The trabecular structure of a proximal femur (StW 522) attributed to Australopithecus africanus exhibits a modern human-like bipedal locomotor pattern, while that of a geologically younger specimen (StW 311) attributed to either Homo sp. or Paranthropus robustus exhibits a pattern more similar to nonhuman apes, potentially suggesting regular bouts of both climbing and terrestrial bipedalism. Our results demonstrate distinct morphological differences, linked to behavioral differences between Australopithecus and later hominins in South Africa and contribute to the increasing evidence of locomotor diversity within the hominin clade.
  • Synek, A., Lu, S., Nauwelaerts, S., Pahr, D. and Kivell, T. (2020). Metacarpophalangeal joint loads during bonobo locomotion: model predictions vs. proxies. Interface [Online] 17. Available at: https://dx.doi.org/10.1098/rsif.2020.0032.
    The analysis of internal trabecular and cortical bone has been an informative tool for drawing inferences about behaviour in extant and fossil primate taxa. Within the hand, metacarpal bone architecture has been shown to correlate well with primate locomotion; however, the extent of morphological differences across taxa is unexpectedly small given the variability in hand use. One explanation for this observation is that the activity-related differences in the joint loads acting on the bone are simply smaller than estimated based on commonly used proxies (i.e. external loading and joint posture), which neglect the influence of muscle forces. In this study, experimental data and a musculoskeletal finger model are used to test this hypothesis by comparing differences between climbing and knuckle-walking locomotion of captive bonobos (Pan paniscus) based on (i) joint load magnitude and direction predicted by the models and (ii) proxy estimations. The results showed that the activity-related differences in predicted joint loads are indeed much smaller than the proxies would suggest, with joint load magnitudes being almost identical between the two locomotor modes. Differences in joint load directions were smaller but still evident, indicating that joint load directions might be a more robust indicator of variation in hand use than joint load magnitudes. Overall, this study emphasizes the importance of including muscular forces in the interpretation of skeletal remains and promotes the use of musculoskeletal models for correct functional interpretations.
  • Dunmore, C., Bardo, A., Skinner, M. and Kivell, T. (2019). Trabecular variation in the first metacarpal and manipulation in hominids. American Journal of Physical Anthropology [Online]. Available at: https://doi.org/10.1002/ajpa.23974.
    Objectives: The dexterity of fossil hominins is often inferred by assessing the comparative manual anatomy and behaviors of extant hominids, with a focus on the thumb. The aim of this study is to test whether trabecular structure is consistent with what is currently known about habitually loaded thumb postures across extant hominids. Materials and methods: We analyze first metacarpal (Mc1) subarticular trabecular architecture in humans (Homo sapiens, n = 10), bonobos (Pan paniscus, n = 10), chimpanzees (Pan troglodytes, n = 11), as well as for the first time, gorillas (Gorilla gorilla gorilla, n = 10) and orangutans (Pongo sp., n = 1, Pongo abelii, n = 3 and Pongo pygmaeus, n = 5). Using a combination of subarticular and whole‐epiphysis approaches, we test for significant differences in relative trabecular bone volume (RBV/TV) and degree of anisotropy (DA) between species. Results: Humans have significantly greater RBV/TV on the radiopalmar aspects of both the proximal and distal Mc1 subarticular surfaces and greater DA throughout the Mc1 head than other hominids. Nonhuman great apes have greatest RBV/TV on the ulnar aspect of the Mc1 head and the palmar aspect of the Mc1 base. Gorillas possessed significantly lower DA in the Mc1 head than any other taxon in our sample. Discussion: These results are consistent with abduction of the thumb during forceful “pad‐to‐pad” precision grips in humans and, in nonhuman great apes, a habitually adducted thumb that is typically used in precision and power grips. This comparative context will help infer habitual manipulative and locomotor grips in fossil hominins.
  • Synek, A., Lu, S., Vereecke, E., Nauwelaerts, S., Kivell, T. and Pahr, D. (2019). Musculoskeletal models of a human and bonobo finger: parameter identification and comparison to in vitro experiments. PeerJ [Online] 7. Available at: https://dx.doi.org/10.7717/peerj.7470.
    Introduction: Knowledge of internal finger loading during human and non-human primate activities such as tool use or knuckle-walking has become increasingly important to reconstruct the behaviour of fossil hominins based on bone morphology. Musculoskeletal models have proven useful for predicting these internal loads during human activities, but load predictions for non-human primate activities are missing due to a lack of suitable finger models. The main goal of this study was to implement both a human and a representative non-human primate finger model to facilitate comparative studies on metacarpal bone loading. To ensure that the model predictions are sufficiently accurate, the specific goals were: (1) to identify species-specific model parameters based on in vitro measured fingertip forces resulting from single tendon loading and (2) to evaluate the model accuracy of predicted fingertip forces and net metacarpal bone loading in a different loading scenario.

    Materials & Methods: Three human and one bonobo (Pan paniscus) fingers were tested in vitro using a previously developed experimental setup. The cadaveric fingers were positioned in four static postures and load was applied by attaching weights to the tendons of the finger muscles. For parameter identification, fingertip forces were measured by loading each tendon individually in each posture. For the evaluation of model accuracy, the extrinsic flexor muscles were loaded simultaneously and both the fingertip force and net metacarpal bone force were measured. The finger models were implemented using custom Python scripts. Initial parameters were taken from literature for the human model and own dissection data for the bonobo model. Optimized model parameters were identified by minimizing the error between predicted and experimentally measured fingertip forces. Fingertip forces and net metacarpal bone loading in the combined loading scenario were predicted using the optimized models and the remaining error with respect to the experimental data was evaluated. Results. The parameter identification procedure led to minor model adjustments but considerably reduced the error in the predicted fingertip forces (root mean square error reduced from 0.53/0.69 N to 0.11/0.20 N for the human/bonobo model). Both models remained physiologically plausible after the parameter identification. In the combined loading scenario, fingertip and net metacarpal forces were predicted with average directional errors below 6◦ and magnitude errors below 12%. Conclusions. This study presents the first attempt to implement both a human and nonhuman primate finger model for comparative palaeoanthropological studies. The good agreement between predicted and experimental forces involving the action of extrinsic flexors—which are most relevant for forceful grasping—shows that the models are likely sufficiently accurate for comparisons of internal loads occurring during human and non-human primate manual activities.
  • Galletta, L., Stephens, N., Bardo, A., Kivell, T. and Marchi, D. (2019). Three-dimensional geometric morphometric analysis of the first metacarpal distal articular surface in humans, great apes and fossil hominins. Journal of Human Evolution [Online] 132:119-136. Available at: https://doi.org/10.1016/j.jhevol.2019.04.008.
    Understanding the manual abilities of fossil hominins has been a focus of palaeoanthropological research for decades. Of interest are the morphological characteristics of the thumb due to its fundamental role in manipulation, particularly that of the trapeziometacarpal joint. Considerably less attention has been given to the thumb metacarpophalangeal (MCP) joint, which plays a role in stabilizing the thumb during forceful grasps and precision pinching. In this study we use a three-dimensional geometric morphometric approach to quantify the shape of the first metacarpal head in extant hominids (Homo, Pan, Gorilla and Pongo) and six fossil hominin species (Homo neanderthalensis Tabun C1 and La Chappelle-aux-Saints, Homo naledi U.W. 101-1282, Australopithecus sediba MH2, Paranthropus robustus/early Homo SK84, Australopithecus africanus StW 418, Australopithecus afarensis A.L. 333w-39), with the aims of identifying shapes that may be correlated with human-like forceful opposition and determining if similar morphologies are present in fossil hominins. Results show that humans differ from extant great apes by having a distally flatter articular surface, larger epicondyle surface area, and a larger radial palmar condyle. We suggest that this suite of features is correlated with a lower range of motion at the MCP joint, which would enhance the thumbs ability to resist the elevated loads associated with the forceful precision grips typical of humans. Great ape genera are each differentiated by distinctive morphological features, each of which is consistently correlated with the predicted biomechanical demands of their particular locomotor and/or manipulatory habits. Neanderthals and U.W. 101-1282 fall within the modern human range of variation, StW 418, SK 84 and U.W. 88-119 fall in between humans and great apes, and A.L. 333w-39 falls within Pan variation. These results agree with those of traditional linear analyses while providing a more comprehensive quantitative basis from which to interpret the hand functional morphology of extinct hominins.
  • Dunmore, C., Kivell, T., Bardo, A. and Skinner, M. (2019). Metacarpal trabecular bone varies with distinct hand-positions used in hominid locomotion. Journal of Anatomy [Online] 235:45-66. Available at: https://doi.org/10.1111/joa.12966.
    Trabecular bone remodels during life in response to loading and thus should, at least in part, reflect potential variation in the magnitude, frequency and direction of joint loading across different hominid species. Here we analyse the trabecular structure across all non-pollical metacarpal distal heads (Mc2-5) in extant great apes, expanding on previous volume of interest and whole-epiphysis analyses that have largely focussed on only the first or third metacarpal. Specifically, we employ both a univariate statistical mapping and a multivariate approach to test for both inter-ray and interspecific differences in relative trabecular bone volume fraction (RBV/TV) and degree of anisotropy (DA) in Mc2-5 subchondral trabecular bone. Results demonstrate that while DA values only separate Pongo from African apes (Pan troglodytes, Pan paniscus, Gorilla gorilla), RBV/TV distribution varies with the predicted loading of the metacarpophalangeal (McP) joints during locomotor behaviours in each species. Gorilla exhibits a relatively dorsal distribution of RBV/TV consistent with habitual hyper-extension of the McP joints during knuckle-walking, whereas Pongo has a palmar distribution consistent with flexed McP joints used to grasp arboreal substrates. Both Pan species possess a disto-dorsal distribution of RBV/TV, compatible with multiple hand postures associated with a more varied locomotor regime. Further inter-ray comparisons reveal RBV/TV patterns consistent with varied knuckle-walking postures in Pan species in contrast to higher RBV/TV values toward the midline of the hand in Mc2 and Mc5 of Gorilla, consistent with habitual palm-back knuckle-walking. These patterns of trabecular bone distribution and structure reflect different behavioural signals that could be useful for determining the behaviours of fossil hominins.
  • Synek, A., Dunmore, C., Kivell, T., Skinner, M. and Pahr, D. (2019). Inverse remodelling algorithm identifies habitual manual activities of primates based on metacarpal bone architecture. Biomechanics and Modeling in Mechanobiology [Online] 18:399-410. Available at: https://doi.org/10.1007/s10237-018-1091-y.
    Previously, a micro-finite element (micro-FE)-based inverse remodelling method was presented in the literature that reconstructs the loading history of a bone based on its architecture alone. Despite promising preliminary results, it remains unclear whether this method is sensitive enough to detect differences of bone loading related to pathologies or habitual activities. The goal of this study was to test the sensitivity of the inverse remodelling method by predicting joint loading histories of metacarpal bones of species with similar anatomy but clearly distinct habitual hand use. Three groups of habitual hand use were defined using the most representative primate species: manipulation (human), suspensory locomotion (orangutan), and knuckle-walking locomotion (bonobo, chimpanzee, gorilla). Nine to ten micro-computed tomography scans of each species ( n=48 in total) were used to create micro-FE models of the metacarpal head region. The most probable joint loading history was predicted by optimally scaling six load cases representing joint postures ranging from −75∘ (extension) to +75∘ (flexion). Predicted mean joint load directions were significantly different between knuckle-walking and non-knuckle-walking groups ( p<0.05 ) and in line with expected primary hand postures. Mean joint load magnitudes tended to be larger in species using their hands for locomotion compared to species using them for manipulation. In conclusion, this study shows that the micro-FE-based inverse remodelling method is sensitive enough to detect differences of joint loading related to habitual manual activities of primates and might, therefore, be useful for palaeoanthropologists to reconstruct the behaviour of extinct species and for biomedical applications such as detecting pathological joint loading.
  • Georgiou, L., Kivell, T., Pahr, D., Buck, L. and Skinner, M. (2019). Trabecular architecture of the great ape and human femoral head. Journal of Anatomy [Online] 234:679-693. Available at: https://doi.org/10.1111/joa.12957.
    Studies of femoral trabecular structure have shown that the orientation and volume of bone are associated with variation in loading and could be informative about individual joint positioning during locomotion. In this study, we analyse for the first time trabecular bone patterns throughout the femoral head using a whole?epiphysis approach to investigate how potential trabecular variation in humans and great apes relates to differences in locomotor modes. Trabecular architecture was analysed using microCT scans of Pan troglodytes (n = 20), Gorilla gorilla (n = 14), Pongo sp. (n = 5) and Homo sapiens (n = 12) in medtool 4.1. Our results revealed differences in bone volume fraction (BV/TV) distribution patterns, as well as overall trabecular parameters of the femoral head between great apes and humans. Pan and Gorilla showed two regions of high BV/TV in the femoral head, consistent with hip posture and loading during two discrete locomotor modes: knuckle?walking and climbing. Most Pongo specimens also displayed two regions of high BV/TV, but these regions were less discrete and there was more variability across the sample. In contrast, Homo showed only one main region of high BV/TV in the femoral head and had the lowest BV/TV, as well as the most anisotropic trabeculae. The Homo trabecular structure is consistent with stereotypical loading with a more extended hip compared with great apes, which is characteristic of modern human bipedalism. Our results suggest that holistic evaluations of femoral head trabecular architecture can reveal previously undetected patterns linked to locomotor behaviour in extant apes and can provide further insight into hip joint loading in fossil hominins and other primates.
  • Rios, L., Kivell, T., Lalueza-Fox, C., Estalrrich, A., García-Tabernero, A., Huguet, R., Quintino, Y., de la Rasilla, M. and Rosas, A. (2019). Skeletal anomalies in the Neandertal family of El Sidron (Spain) support a role of inbreeding in Neandertal extinction. Scientific Reports [Online] 9. Available at: https://doi.org/10.1038/s41598-019-38571-1.
    Neandertals disappeared from the fossil record around 40,000 bp, after a demographic history of small and isolated groups with high but variable levels of inbreeding, and episodes of interbreeding with other Paleolithic hominins. It is reasonable to expect that high levels of endogamy could be expressed in the skeleton of at least some Neandertal groups. Genetic studies indicate that the 13 individuals from the site of El Sidrón, Spain, dated around 49,000 bp, constituted a closely related kin group, making these Neandertals an appropriate case study for the observation of skeletal signs of inbreeding. We present the complete study of the 1674 identified skeletal specimens from El Sidrón. Altogether, 17 congenital anomalies were observed (narrowing of the internal nasal fossa, retained deciduous canine, clefts of the first cervical vertebra, unilateral hypoplasia of the second cervical vertebra, clefting of the twelfth thoracic vertebra, diminutive thoracic or lumbar rib, os centrale carpi and bipartite scaphoid, tripartite patella, left foot anomaly and cuboid-navicular coalition), with at least four individuals presenting congenital conditions (clefts of the first cervical vertebra). At 49,000 years ago, the Neandertals from El Sidrón, with genetic and skeletal evidence of inbreeding, could be representative of the beginning of the demographic collapse of this hominin phenotype.
  • Key, A., Merrit, S. and Kivell, T. (2018). Hand grip diversity and frequency during the use of Lower Palaeolithic stone cutting-tools. Journal of Human Evolution [Online] 125:137-158. Available at: https://dx.doi.org/10.1016/j.jhevol.2018.08.006.
    The suite of anatomical features contributing to the unique gripping capabilities of the modern human hand evolved alongside the proliferation of Lower Palaeolithic flaked tool technologies across the Old World. Experimental studies investigating their potential co-evolution suggest that the use of flakes, handaxes, and other stone tools is facilitated by manipulative capabilities consistent with the evolutionary trajectory of the hominin hand during this period. Grip analyses have provided important contributions to this understanding. To date, however, there has been no large-scale investigation of grip diversity during flaked stone-tool use, empirical comparative analyses of grip use frequencies, or examination of ergonomic relationships between grip choice and stone tool type and form.

    Here, we conduct four experimental studies, using replica Lower Palaeolithic stone tools in a series of actualistic and laboratory-based contexts, to record grip type and frequency of grip use during 1067 stone tool-use events by 123 individuals. Using detailed morphometric data recorded from each tool, we demonstrate how grip choice varies according to the type and form of stone tool used, and how these relationships differ between tool-use contexts. We identify 29 grip types across all tool-use events, with significant differences recorded in their frequency of use dependent on tool type, tool form, and the context of use. Despite the influence of these three factors, there is consistency in the frequent use of a limited number (?4) of grip types within each experiment and the consistent and seemingly forceful recruitment of the thumb and index finger. Accordingly, we argue that there are deep-rooted, ergonomically-related, regularities in how stone tools are gripped during their use, that these regularities may have been present during the use of stone tools by Plio-Pleistocene hominins, and any subsequent selective pressures would likely have been focused on the first and second digit.
  • Bardo, A., Vigouroux, L., Kivell, T. and Pouydebat, E. (2018). The impact of hand proportions on tool grip abilities in humans, great apes and fossil hominins: a biomechanical analysis using musculoskeletal simulation. Journal of Human Evolution [Online] 125:106-121. Available at: https://dx.doi.org/10.1016/j.jhevol.2018.10.001.
    Differences in grip techniques used across primates are usually attributed to variation in thumb-finger proportions and muscular anatomy of the hand. However, this cause-effect relationship is not fully understood because little is known about the biomechanical functioning and mechanical loads (e.g., muscle or joint forces) of the non-human primate hand compared to that of humans during object manipulation. This study aims to understand the importance of hand proportions on the use of different grip strategies used by humans, extant great apes (bonobos, gorillas and orangutans) and, potentially, fossil hominins (Homo naledi and Australopithecus sediba) using a musculoskeletal model of the hand. Results show that certain grips are more challenging for some species, particularly orangutans, than others, such that they require stronger muscle forces for a given range of motion. Assuming a human-like range of motion at each hand joint, simulation results show that H. naledi and A. sediba had the biomechanical potential to use the grip techniques considered important for stone tool-related behaviors in humans. These musculoskeletal simulation results shed light on the functional consequences of the different hand proportions among extant and extinct hominids and the different manipulative abilities found in humans and great apes.
  • Kivell, T., Davenport, R., Hublin, J., Thackeray, J. and Skinner, M. (2018). Trabecular architecture and joint loading of the proximal humerus in extant hominoids, Ateles, and Australopithecus africanus. American Journal of Physical Anthropology [Online] 167:348-365. Available at: https://doi.org/10.1002/ajpa.23635.
    Objectives: Several studies have investigated potential functional signals in the trabecular structure of the primate proximal humerus but with varied success. Here we apply for the first time a ìwhole-epiphysesî approach to analysing trabecular bone in the humeral head with the aim of providing a more holistic interpretation of trabecular variation in relation to habitual locomotor or manipulative behaviors in several extant primates and Australopithecus africanus.

    Materials and Methods: We use a ìwhole-epiphysisî methodology in comparison to the traditional volume of interest (VOI) approach to investigate variation in trabecular structure and joint loading in the proximal humerus of extant hominoids, Ateles and A. africanus (StW 328).

    Results: There are important differences in the quantification of trabecular parameters using a ìwhole-epiphysisî versus a VOI-based approach. Variation in trabecular structure across knucklewalking African apes, suspensory taxa, and modern humans was generally consistent with predictions of load magnitude and inferred joint posture during habitual behaviors. Higher relative trabecular bone volume and more isotropic trabeculae in StW 328 suggest A. africanus may have still used its forelimbs for arboreal locomotion.

    Discussion: A whole-epiphysis approach to analysing trabecular structure of the proximal humerus can help distinguish functional signals of joint loading across extant primates and can provide novel insight into habitual behaviors of fossil hominins.
  • Lu, S., Vereecke, E., Synek, A., Pahr, D. and Kivell, T. (2018). A novel experimental design for the measurement of metacarpal bone loading and deformation and fingertip force. PeerJ [Online]:1 -19. Available at: https://doi.org/10.7717/peerj.5480.
    Background: Musculoskeletal and finite element modelling are often used to predict joint loading and bone strength within the human hand, but there is a lack of in vitro evidence of the force and strain experienced by hand bones.

    Methods: This study presents a novel experimental setup that allows the positioning of a cadaveric digit in a variety of postures with the measurement of force and strain experienced by the third metacarpal. The setup allows for the measurement of fingertip force as well. We tested this experimental setup using three cadaveric human third digits in which the flexor tendons were loaded in two tendon pathways: (1) parallel to the metacarpal bone shaft, with bowstringing; (2) a semi-physiological condition in which the tendons were positioned closer to the bone shaft.

    Results: There is substantial variation in metacarpal net force, metacarpal strain and fingertip force between the two tendon pathways. The net force acting on the metacarpal bone is oriented palmarly in the parallel tendon condition, causing tension along the dorsum of the metacarpal shaft, while the force increases and is oriented dorsally in the semi-physiological condition, causing compression of the dorsal metacarpal shaft. Fingertip force is also greater in the semi-physiological condition, implying a more efficient grip function. Inter-individual variation is observed in the radioulnar orientation of the force experienced by the metacarpal bone, the fingertip force, and the strain patterns on the metacarpal shaft.

    Conclusion: This study demonstrates a new method for measuring force and strain experienced by the metacarpal, and fingertip force in cadaveric digits that can, in turn, inform computation models. Inter-individual variation in loads experienced by the third digit suggest that there are differences in joint contact and/or internal bone structure across individuals that are important to consider in clinical and evolutionary contexts.
  • Tsegai, Z., Skinner, M., Pahr, D., Hublin, J. and Kivell, T. (2018). Ontogeny and variability of trabecular bone in the chimpanzee humerus, femur and tibia. American Journal of Physical Anthropology [Online] 138:318-332. Available at: https://doi.org/10.1002/ajpa.23696.
    Although adult skeletal morphological variation is best understood within the framework of age-related processes, relatively little research has been directed towards the structure of and variation in trabecular bone during ontogeny. We report here new quantitative and structural data on trabecular bone microarchitecture in the proximal tibia during growth and development, as demonstrated in a sub adult archaeological skeletal sample from the Late Prehistoric Ohio Valley. These data characterize the temporal sequence and variation in trabecular bone structure and structural parameters during ontogeny as related to the acquisition of normal functional activities and changing body mass. The skeletal sample from the Fort Ancient Period site of SunWatch Village is composed of 33 sub adult and three young adult proximal tibiae. Non-destructive micro CT scanning of the proximal metaphyseal and epiphyseal tibia captures the micro architectural trabecular structure, allowing quantitative structural analyses measuring bone volume fraction, degree of anisotropy, trabecular thickness, and trabecular number. The micro CT resolution effects on structural parameters were analysed. Bone volume fraction and degree of anisotropy are highest at birth, decreasing to low values at 1 year of age, and then gradually increasing to the adult range around 6-8 years of age. Trabecular number is highest at birth and lowest at skeletal maturity; trabecular thickness is lowest at birth and highest at skeletal maturity. The results of this study highlight the dynamic sequential relationships between growth/development, general functional activities, and trabecular distribution and architecture, providing a reference for comparative studies.
  • Kivell, T., Churchill, S., Kibii, J., Schmid, P. and Berger, L. (2018). The hand of Australopithecus sediba. PaleoAnthropology [Online]:282-333. Available at: http://dx.doi.org/10.4207/PA.2018.ART115.
    Here we describe the functional morphology of the Australopithecus sediba hand, including the almost complete hand of the presumed female Malapa Hominin (MH) 2 skeleton and a single, juvenile metacarpal from the presumed male MH1 skeleton. Qualitative and quantitative comparisons with extant hominids and fossil hominins, ranging from Ardipithecus to early Homo sapiens, reveal that Au. sediba presents a unique suite of morphological features that have not been found in any other known hominin. Analyses of intrinsic hand proportions show that the MH2 hand has a thumb that is longer relative to its fingers than recent humans and any other known hominin. Furthermore, the morphology of the hamatometacarpal articulation suggests that the robust fifth metacarpal was positioned in a slightly more flexed and adducted posture than is typical of Neandertals and humans. Together, this morphology would have facilitated opposition of the thumb to the fingers and pad-to-pad precision gripping that is typical of later Homo. However, the remarkably gracile morphology of the first ray and the morphology of the lateral carpometacarpal region suggest limited force production by the thumb. The distinct scaphoid-lunatecapitate morphology in MH2 suggests a greater range of abduction at the radiocarpal joint and perhaps less central-axis loading of the radiocarpal and midcarpal joints than is interpreted for other fossil hominins, while the morphology of the hamatotriquetrum articulation suggests enhanced stability of the medial midcarpal joint in extended and/or adducted wrist postures. The MH2 proximal phalanges show moderate curvature and, unusually, both the proximal and intermediate phalanges have well-developed flexor sheath ridges that, in combination with a palmarly-projecting hamate hamulus, suggest powerful flexion and that some degree of arboreality may have been a functionally important part of the Au. sediba locomotor repertoire. Finally, the MH1 and MH2 third metacarpals differ remarkably in their size and degree of robusticity, but this variation fits comfortably within the sexual dimorphism documented in recent humans and other fossil hominins, and does not necessarily reflect differences in function or hand use. Overall, the morphology of the current Au. sediba hand bones suggests the capability for use of the hands both for powerful gripping during locomotion and precision manipulation that is required for tool-related behaviors, but likely with more limited force production by the thumb than is inferred in humans, Neandertals, and potentially Homo naledi.
  • Stephens, N., Kivell, T., Pahr, D., Hublin, J. and Skinner, M. (2018). Trabecular bone patterning across the human hand. Journal of Human Evolution [Online] 123:1-23. Available at: https://doi.org/10.1016/j.jhevol.2018.05.004.
    Hand bone morphology is regularly used to link particular hominin species with behaviors relevant to cognitive/technological progress. Debates about the functional significance of differing hominin hand bone morphologies tend to rely on establishing phylogenetic relationships and/or inferring behavior from epigenetic variation arising from mechanical loading and adaptive bone modeling. Most research focuses on variation in cortical bone structure, but additional information about hand function may be provided through the analysis of internal trabecular structure. While primate hand bone trabecular structure is known to vary in ways that are consistent with expected joint loading differences during manipulation and locomotion, no study exists that has documented this variation across the numerous bones of the hand. We quantify the trabecular structure in 22 bones of the human hand (early/extant modern Homo sapiens) and compare structural variation between two groups associated with post-agricultural/industrial (post-Neolithic) and foraging/hunter-gatherer (forager) subsistence strategies. We (1) establish trabecular bone volume fraction (BV/TV), modulus (E), degree of anisotropy (DA), mean trabecular thickness (Tb.Th) and spacing (Tb.Sp); (2) visualize the average distribution of site-specific BV/TV for each bone; and (3) examine if the variation in trabecular structure is consistent with expected joint loading differences among the regions of the hand and between the groups. Results indicate similar distributions of trabecular bone in both groups, with those of the forager sample presenting higher BV/TV, E, and lower DA, suggesting greater and more variable loading during manipulation. We find indications of higher loading along the ulnar side of the forager sample hand, with high site-specific BV/TV distributions among the carpals that are suggestive of high loading while the wrist moves through the ‘dart-thrower's’ motion. These results support the use of trabecular structure to infer behavior and have direct implications for refining our understanding of human hand evolution and fossil hominin hand use.
  • Neufuss, J., Robbins, M., Baeumer, J., Humle, T. and Kivell, T. (2018). Manual skills for food processing by mountain gorillas in Bwindi Impenetrable National Park, Uganda. Biological Journal of the Linnean Society [Online] 127:543-562. Available at: https://doi.org/10.1093/biolinnean/bly071.
    Although gorillas rarely use tools in the wild, their manipulative skills during plant processing may be similar to those of other tool-using great apes. Virunga mountain gorillas are known for the complexity in their methods of thistle and nettle plant preparation in the wild. However, there has been no comparable data on food processing in the population of mountain gorillas from the Bwindi Impenetrable National Park, Uganda. We investigated the manual actions and hand grips used when accessing edible parts of two hard-to-process plants defended by stinging hairs, epidermis or periderm (i.e., peel of Urera hypselodendron and pith of Mimulopsis arborescens) and one undefended plant (i.e., leaves of Momordica foetida) in 11 Bwindi wild mountain gorillas (Gorilla beringei beringei) using video records ad libitum. Similar to thistle feeding by Virunga gorillas, Bwindi gorillas used the greatest number of manual actions for the most hard-to-process plant (U. hypselodendron), the actions were ordered in several key stages and organised hierarchically. The demands of processing plant material elicited 19 different grips and variable thumb postures, of which three grips were new and 16 grips have either been previously reported or show clear similarities to grips used by other wild and captive African apes and humans. Moreover, our study only partly supports a functional link between diet and hand morphology in mountain gorillas and suggests that the gorilla hand is best adapted to forceful grasping that is required for both manipulation and arboreal locomotion.
  • Georgiou, L., Kivell, T., Pahr, D. and Skinner, M. (2018). Trabecular bone patterning in the hominoid distal femur. PeerJ [Online]. Available at: https://doi.org/10.7717/peerj.5156.
    In addition to external bone shape and cortical bone thickness and distribution, the distribution and orientation of internal trabecular bone across individuals and species has yielded important functional information on how bone adapts in response to load. In particular, trabecular bone analysis has played a key role in studies of human and nonhuman primate locomotion and has shown that species with different locomotor repertoires display distinct trabecular architecture in various regions of the skeleton. In this study, we analyse trabecular structure throughout the distal femur of extant hominoids and test for differences due to locomotor loading regime.
  • Neufuss, J., Robbins, M., Baeumer, J., Humle, T. and Kivell, T. (2018). Gait characteristics of vertical climbing in mountain gorillas and chimpanzees. Journal of Zoology [Online] 306:129-138. Available at: https://doi.org/10.1111/jzo.12577.
    Biomechanical analyses of arboreal locomotion in great apes in their natural environment are scarce and thus attempts to correlate behavioural and habitat differences with variations in morphology are limited. The aim of this study was to investigate the gait characteristics of vertical climbing in mountain gorillas (Gorilla beringei beringei) and chimpanzees (Pan troglodytes) in a natural environment to assess differences in the climbing styles that may relate to variation in body size. We investigated temporal variables (i.e., cycle duration, duty factors, and stride frequency) and footfall sequences (i.e., diagonal vs. lateral sequence gaits) during vertical climbing (both ascent and descent) in 11 wild mountain gorillas and compared these data to those of eight semi-free-ranging chimpanzees, using video records ad libitum. Comparisons of temporal gait parameters revealed that largebodied mountain gorillas exhibited a longer cycle duration, lower stride frequency and generally a higher duty factor than smaller-bodied chimpanzees. While both apes were similarly versatile in their vertical climbing performance in the natural environment, mountain gorillas most often engaged in diagonal sequence/diagonal couplet gaits and chimpanzees most often used lateral sequence/diagonal couplet gaits. This study revealed that mountain gorillas adapt their climbing strategy to accommodate their large body mass in a similar manner previously found in captive western lowland gorillas, and that chimpanzees are less variable in their climbing strategy than has been documented in captive bonobos.
  • Samuel, D., Nauwelaerts, S., Stevens, J. and Kivell, T. (2018). Hand pressures during arboreal locomotion in captive bonobos (Pan paniscus). Journal of Experimental Biology [Online] 221:jeb170910. Available at: http://dx.doi.org/10.1242/jeb.170910.
    Evolution of the human hand has undergone a transition from use during locomotion to use primarily for manipulation. Previous comparative morphological and biomechanical studies have focused on potential changes in manipulative abilities during human hand evolution, but few have focused on functional signals for arboreal locomotion. Here, we provide this comparative context though the first analysis of hand loading in captive bonobos during arboreal locomotion. We quantify pressure experienced by the fingers, palm and thumb in bonobos during vertical locomotion, suspension and arboreal knuckle-walking. Results show that pressure experienced by the fingers is significantly higher during knuckle-walking compared with similar pressures experienced by the fingers and palm during suspensory and vertical locomotion. Peak pressure is most often experienced at or around the third digit in all locomotor modes. Pressure quantified for the thumb is either very low or absent, despite the thumb making contact with the substrate during all suspensory and vertical locomotor trials. Unlike chimpanzees, the bonobos do not show a rolling pattern of digit contact with the substrate during arboreal knuckle-walking but, instead, digits 3 and 4 typically touch down first and digit 5 almost always made contact with the substrate. These results have implications for interpreting extant and fossilised hand morphology; we expect bonobo (and chimpanzee) bony morphology to primarily reflect the biomechanical loading of knuckle-walking, while functional signals for arboreal locomotion in fossil hominins are most likely to appear in the fingers, particularly digit 3, and least likely to appear in the morphology of the thumb.
  • Groucutt, H., Grun, R., Zalmout, I., Drake, N., Armitage, S., Candy, I., Clark-Wilson, R., Louys, J., Breeze, P., Duval, M., Buck, L., Kivell, T., Pomeroy, E., Stephens, N., Stock, J., Stewart, M., Price, G., Kinsley, L., Sung, W., Alsharekh, A., Al-Omari, A., Zahir, M., Memesh, A., Abdulshakoor, A., Al-Masari, A., Bahameem, A., Al Murayyi, K., Zahrani, B., Scerri, E. and Petraglia, M. (2018). Homo sapiens in Arabia by 85,000 years ago. Nature Ecology and Evolution [Online] 2:800-809. Available at: https://doi.org/10.1038/s41559-018-0518-2.
    Understanding the timing and character of the expansion of Homo sapiens out of Africa is critical for inferring the colonization and admixture processes that underpin global population history. It has been argued that dispersal out of Africa had an early phase, particularly ~130–90 thousand years ago (ka), that reached only the East Mediterranean Levant, and a later phase, ~60–50 ka, that extended across the diverse environments of Eurasia to Sahul. However, recent findings from East Asia and Sahul challenge this model. Here we show that H. sapiens was in the Arabian Peninsula before 85 ka. We describe the Al Wusta-1 (AW-1) intermediate phalanx from the site of Al Wusta in the Nefud desert, Saudi Arabia. AW-1 is the oldest directly dated fossil of our species outside Africa and the Levant. The palaeoenvironmental context of Al Wusta demonstrates that H. sapiens using Middle Palaeolithic stone tools dispersed into Arabia during a phase of increased precipitation driven by orbital forcing, in association with a primarily African fauna. A Bayesian model incorporating independent chronometric age estimates indicates a chronology for Al Wusta of ~95–86 ka, which we correlate with a humid episode in the later part of Marine Isotope Stage 5 known from various regional records. Al Wusta shows that early dispersals were more spatially and temporally extensive than previously thought. Early H. sapiens dispersals out of Africa were not limited to winter rainfall-fed Levantine Mediterranean woodlands immediately adjacent to Africa, but extended deep into the semi-arid grasslands of Arabia, facilitated by periods of enhanced monsoonal rainfall.
  • Williams-Hatala, E., Hatala, K., Gordon, M., Key, A., Kasper, M. and Kivell, T. (2018). The manual pressures of stone tool behaviors and their implications for the evolution of the human hand. Journal of Human Evolution [Online] 119:14-26. Available at: https://doi.org/10.1016/j.jhevol.2018.02.008.
    It is widely agreed that biomechanical stresses imposed by stone tool behaviors influenced the evolution of the human hand. Though archaeological evidence suggests that early hominins participated in a variety of tool behaviors, it is unlikely that all behaviors equally influenced modern human hand anatomy. It is more probable that a behavior's likelihood of exerting a selective pressure was a weighted function of the magnitude of stresses associated with that behavior, the benefits received from it, and the amount of time spent performing it. Based on this premise, we focused on the first part of that equation and evaluated magnitudes of stresses associated with stone tool behaviors thought to have been commonly practiced by early hominins, to determine which placed the greatest loads on the digits. Manual pressure data were gathered from 39 human subjects using a Novel Pliance® manual pressure system while they participated in multiple Plio-Pleistocene tool behaviors: nut-cracking, marrow acquisition with a hammerstone, flake production with a hammerstone, and handaxe and flake use. Manual pressure distributions varied significantly according to behavior, though there was a tendency for regions of the hand subject to the lowest pressures (e.g., proximal phalanges) to be affected less by behavior type. Hammerstone use during marrow acquisition and flake production consistently placed the greatest loads on the digits collectively, on each digit and on each phalanx. Our results suggest that, based solely on the magnitudes of stresses, hammerstone use during marrow acquisition and flake production are the most likely of the assessed behaviors to have influenced the anatomical and functional evolution of the human hand.
  • Tsegai, Z., Skinner, M., Pahr, D., Hublin, J. and Kivell, T. (2018). Systemic patterns of trabecular bone across the human and chimpanzee skeleton. Journal of Anatomy [Online] 232:641-656. Available at: https://doi.org/10.1111/joa.12776.
    Aspects of trabecular bone architecture are thought to reflect regional loading of the skeleton, and thus differ between primate taxa with different locomotor and postural modes. However, there are several systemic factors that affect bone structure that could contribute to, or be the primary factor determining, interspecific differences in bone structure. These systemic factors include differences in genetic regulation, sensitivity to loading, hormone levels, diet, and/or activity levels. Improved understanding of inter/intraspecific variability, and variability across the skeleton of an individual, is required to properly interpret potential functional signals present within trabecular structure. Using a whole-region method of analysis, we investigated trabecular structure throughout the skeleton of humans and chimpanzees. Trabecular bone volume fraction (BV/TV), degree of anisotropy (DA) and trabecular thickness (Tb.Th) were quantified from high resolution micro-computed tomographic scans of the humeral and femoral head, third metacarpal and third metatarsal head, distal tibia, talus and first thoracic vertebra. We find that BV/TV is, in most anatomical sites, significantly higher in chimpanzees than in humans, suggesting a systemic difference in trabecular structure unrelated to local loading regime. Differences in BV/TV between the forelimb and hindlimb do not clearly reflect differences in locomotor loading in the study taxa. There are no clear systemic differences between the taxa in DA and, as such, this parameter may reflect function and relate to differences in joint loading. This systemic approach reveals both the pattern of variability across the skeleton and between taxa, and helps identify those features of trabecular structure that may relate to joint function.
  • Kivell, T., Rosas, A., Estalrrich, A., Huguet, R., Garcia-Tabernero, A., Rios, L. and de la Rasilla, M. (2017). New Neandertal wrist bones from El Sidrón, Spain (1994-2009). Journal of Human Evolution [Online] 114:45-75. Available at: https://doi.org/10.1016/j.jhevol.2017.09.007.
    Twenty-nine carpal bones of Homo neanderthalensis have been recovered from the site of El Sidrón (Asturias, Spain) during excavations between 1994 and 2009, alongside ?2500 other Neandertal skeletal elements dated to ?49,000 years ago. All bones of the wrist are represented, including adult scaphoids (n = 6), lunates (n = 2), triquetra (n = 4), pisiforms (n = 2), trapezia (n = 2), trapezoids (n = 5), capitates (n = 5), and hamates (n = 2), as well as one fragmentary and possibly juvenile scaphoid. Several of these carpals appear to belong to the complete right wrist of a single individual. Here we provide qualitative and quantitative morphological descriptions of these carpals, within a comparative context of other European and Near Eastern Neandertals, early and recent Homo sapiens, and other fossil hominins, including Homo antecessor, Homo naledi, and australopiths.

    Overall, the El Sidrón carpals show characteristics that typically distinguish Neandertals from H. sapiens, such as a relatively flat first metacarpal facet on the trapezium and a more laterally oriented second metacarpal facet on the capitate. However, there are some distinctive features of the El Sidrón carpals compared with most other Neandertals. For example, the tubercle of the trapezium is small with limited projection, while the scaphoid tubercle and hamate hamulus are among the largest seen in other Neandertals. Furthermore, three of the six adult scaphoids show a distinctive os-centrale portion, while another is a bipartite scaphoid with a truncated tubercle. The high frequency of rare carpal morphologies supports other evidence of a close genetic relationship among the Neandertals found at El Sidrón.
  • Neufuss, J., Robbins, M., Baeumer, J., Humle, T. and Kivell, T. (2017). Comparison of hand use and forelimb posture during vertical climbing in mountain gorillas (Gorilla beringei beringei) and chimpanzees (Pan troglodytes). American Journal of Physical Anthropology [Online] 164:651-664. Available at: http://dx.doi.org/10.1002/ajpa.23303.
    Objectives: Studies on grasping and limb posture during arboreal locomotion in great apes in their natural environment are scarce and thus, attempts to correlate behavioral and habitat differences with variation in morphology are limited. The aim of this study is to compare hand use and forelimb posture during vertical climbing in wild, habituated mountain gorillas (Gorilla beringei beringei) and semi-free-ranging chimpanzees (Pan troglodytes) to assess differences in the climbing styles that may relate to variation in hand or forelimb morphology and body size.

    Materials and methods: We investigated hand use and forelimb posture during both ascent and descent vertical climbing in 15 wild mountain gorillas and eight semi-free-ranging chimpanzees, using video records obtained ad libitum.

    Results: In both apes, forelimb posture was correlated with substrate size during both ascent and descent climbing. While climbing, both apes used power grips and diagonal power grips, including three different thumb postures. Mountain gorillas showed greater ulnar deviation of the wrist during vertical descent than chimpanzees, and the thumb played an important supportive role when gorillas vertically descended lianas.

    Discussion: We found that both apes generally had the same grip preferences and used similar forelimb postures on supports of a similar size, which is consistent with their overall similarity in hard and soft tissue morphology of the hand and forelimb. However, some species-specific differences in morphology appear to elicit slightly different grasping strategies during vertical climbing between mountain gorillas and chimpanzees.
  • Tsegai, Z., Skinner, M., Gee, A., Pahr, D., Treece, G., Hublin, J. and Kivell, T. (2017). Trabecular and cortical bone structure of the talus and distal tibia in Pan and Homo. American Journal of Physical Anthropology [Online] 163:784-805. Available at: http://dx.doi.org/10.1002/ajpa.23249.
    Objectives: Internal bone structure, both cortical and trabecular bone, remodels in response to loading and may provide important information regarding behavior. The foot is well suited to analysis of internal bone structure because it experiences the initial substrate reaction forces, due to its proximity to the substrate. Moreover, as humans and apes differ in loading of the foot, this region is relevant to questions concerning arboreal locomotion and bipedality in the hominoid fossil record.

    Materials and methods: We apply a whole-bone/epiphysis approach to analyze trabecular and cortical bone in the distal tibia and talus of Pan troglodytes and Homo sapiens. We quantify bone volume fraction (BV/TV), degree of anisotropy (DA), trabecular thickness (Tb.Th), bone surface to volume ratio (BS/BV), and cortical thickness and investigate the distribution of BV/TV and cortical thickness throughout the bone/epiphysis.

    Results: We find that Pan has a greater BV/TV, a lower BS/BV and thicker cortices than Homo in both the talus and distal tibia. The trabecular structure of the talus is more divergent than the tibia, having thicker, less uniformly aligned trabeculae in Pan compared to Homo. Differences in dorsiflexion at the talocrural joint and in degree of mobility at the talonavicular joint are reflected in the distribution of cortical and trabecular bone.

    Discussion: Overall, quantified trabecular parameters represent overall differences in bone strength between the two species, however, DA may be directly related to joint loading. Cortical and trabecular bone distributions correlate with habitual joint positions adopted by each species, and thus have potential for interpreting joint position in fossil hominoids.
  • Hawks, J., Elliot, M., Schmid, P., Churchill, S., de Ruiter, D., Roberts, E., Hilbert-Wolf, H., Garvin, H., Williams, S., Delezene, L., Feuerriegel, E., Randolph-Quinney, P., Kivell, T., Laird, M., Tawane, G., DeSilva, J., Bailey, S., Brophy, J., Meyer, M., Skinner, M., Tocheri, M., VanSickle, C., Walker, C., Campbell, T., Kuhn, B., Kruger, A., Tucker, S., Gurtov, A., Hlophe, N., Hunter, R., Morris, H., Peixotto, B., Ramalepa, M., van Rooyen, D., Tsikoane, M., Boshoff, P., Dirks, P. and Berger, L. (2017). New fossil remains of Homo naledi from the Lesedi Chamber, South Africa. eLife [Online]. Available at: http://dx.doi.org/10.7554/eLife.24232.
    The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to Homo naledi. Further exploration led to the discovery of hominin material, now comprising 131 hominin specimens, within a second chamber, the Lesedi Chamber. The Lesedi Chamber is far separated from the Dinaledi Chamber within the Rising Star cave system, and represents a second depositional context for hominin remains. In each of three collection areas within the Lesedi Chamber, diagnostic skeletal material allows a clear attribution to H. naledi. Both adult and immature material is present. The hominin remains represent at least three individuals based upon duplication of elements, but more individuals are likely present based upon the spatial context. The most significant specimen is the near-complete cranium of a large individual, designated LES1, with an endocranial volume of approximately 610 ml and associated postcranial remains. The Lesedi Chamber skeletal sample extends our knowledge of the morphology and variation of H. naledi, and evidence of H. naledi from both recovery localities shows a consistent pattern of differentiation from other hominin species.
  • Stephens, N., Kivell, T., Gross, T., Pahr, D., Lazenby, R., Hublin, J., Hershkovitz, I. and Skinner, M. (2016). Trabecular architecture in the thumb of Pan and Homo: implications for investigating hand use, loading, and hand preference in the fossil record. American Journal of Physical Anthropology [Online] 161:603-619. Available at: http://dx.doi.org/10.1002/ajpa.23061.
    Objectives: Humans display an 85–95% cross-cultural right-hand bias in skilled tasks, which is considered a derived behavior because such a high frequency is not reported in wild non-human primates. Handedness is generally considered to be an evolutionary byproduct of selection for manual dexterity and augmented visuo-cognitive capabilities within the context of complex stone tool manufacture/use. Testing this hypothesis requires an understanding of when appreciable levels of right dominant behavior entered the fossil record. Because bone remodels in vivo, skeletal asymmetries are thought to reflect greater mechanical loading on the dominant side, but incomplete preservation of external morphology and ambiguities about past loading environments complicate interpretations. We test if internal trabecular bone is capable of providing additional information by analyzing the thumb of Homo sapiens and Pan.

    Materials and methods: We assess trabecular structure at the distal head and proximal base of paired (left/right) first metacarpals using micro-CT scans of Homo sapiens (n?=?14) and Pan (n?=?9). Throughout each epiphysis we quantify average and local bone volume fraction (BV/TV), degree of anisotropy (DA), and elastic modulus (E) to address bone volume patterning and directional asymmetry.

    Results: We find a right directional asymmetry in H. sapiens consistent with population-level handedness, but also report a left directional asymmetry in Pan that may be the result of postural and/or locomotor loading.

    Conclusion: We conclude that trabecular bone is capable of detecting right/left directional asymmetry, but suggest coupling studies of internal structure with analyses of other skeletal elements and cortical bone prior to applications in the fossil record.
  • Tsegai, Z., Stephens, N., Treece, G., Skinner, M., Kivell, T. and Gee, A. (2016). Cortical bone mapping: An application to hand and foot bones in hominoids. Comptes Rendus Palevol [Online] 16:690-701. Available at: http://dx.doi.org/10.1016/j.crpv.2016.11.001.
    Bone form reflects both the genetic profile and behavioural history of an individual. As cortical bone is able to remodel in response to mechanical stimuli, interspecific differences in cortical bone thickness may relate to loading during locomotion or manual behaviours during object manipulation. Here, we test the application of a novel method of cortical bone mapping to the third metacarpal (Mc3) and talus of Pan, Pongo, and Homo. This method of analysis allows measurement of cortical thickness throughout the bone, and as such is applicable to elements with complex morphology. In addition, it allows for registration of each specimen to a canonical surface, and identifies regions where cortical thickness differs significantly between groups. Cortical bone mapping has potential for application to palaeoanthropological studies; however, due to the complexity of correctly registering homologous regions across varied morphology, further methodological development would be advantageous.
  • Neufuss, J., Humle, T., Cremaschi, A. and Kivell, T. (2016). Nut-cracking behaviour in wild-born, rehabilitated bonobos (Pan paniscus): a comprehensive study of hand preference, hand grips and efficiency. American Journal of Primatology [Online] 79. Available at: http://dx.doi.org/10.1002/ajp.22589.
    There has been an enduring interest in primate tool-use and manipulative abilities, most often with the goal of providing insight into the evolution of human manual dexterity, right-hand preference, and what behaviours make humans unique. Chimpanzees (Pan troglodytes) are arguably the most well-studied tool-users amongst non-human primates, and are particularly well-known for their complex nut-cracking behaviour, which has been documented in several West African populations. However, their sister-taxon, the bonobos (Pan paniscus), rarely engage in even simple tool-use and are not known to nut-crack in the wild. Only a few studies have reported tool-use in captive bonobos, including their ability to crack nuts, but details of this complex tool-use behaviour have not been documented before. Here, we fill this gap with the first comprehensive analysis of bonobo nut-cracking in a natural environment at the Lola ya Bonobo sanctuary, Democratic Republic of the Congo. Eighteen bonobos were studied as they cracked oil palm nuts using stone hammers. Individual bonobos showed exclusive laterality for using the hammerstone and there was a significant group-level right-hand bias. The study revealed 15 hand grips for holding differently sized and weighted hammerstones, 10 of which had not been previously described in the literature. Our findings also demonstrated that bonobos select the most effective hammerstones when nut-cracking. Bonobos are efficient nut-crackers and not that different from the renowned nut-cracking chimpanzees of Bossou, Guinea, which also crack oil palm nuts using stones.
  • Schoonaert, K., D’Aout, K., Samuel, D., Talloen, W., Nauwelaerts, S., Kivell, T. and Aerts, P. (2016). Gait characteristics and spatio-temporal variables of climbing in bonobos (Pan paniscus). American Journal of Primatology [Online] 78:1165-1177. Available at: http://dx.doi.org/10.1002/ajp.22571.
    Although much is known about the terrestrial locomotion of great apes, their arboreal locomotion has been studied less extensively. This study investigates arboreal locomotion in bonobos (Pan paniscus), focusing on the gait characteristics and spatio-temporal variables associated with locomotion on a pole. These features are compared across different substrate inclinations (0°, 30°, 45°, 60°, and 90°), and horizontal quadrupedal walking is compared between an arboreal and a terrestrial substrate. Our results show greater variation in footfall patterns with increasing incline, resulting in more lateral gait sequences. During climbing on arboreal inclines, smaller steps and strides but higher stride frequencies and duty factors are found compared to horizontal arboreal walking. This may facilitate better balance control and dynamic stability on the arboreal substrate. We found no gradual change in spatio-temporal variables with increasing incline; instead, the results for all inclines were clustered together. Bonobos take larger strides at lower stride frequencies and lower duty factors on a horizontal arboreal substrate than on a flat terrestrial substrate. We suggest that these changes are the result of the better grip of the grasping feet on an arboreal substrate. Speed modulation of the spatio-temporal variables is similar across substrate inclinations and between substrate types, suggesting a comparable underlying motor control. Finally, we contrast these variables of arboreal inclined climbing with those of terrestrial bipedal locomotion, and briefly discuss the results with respect to the origin of habitual bipedalism. Am. J. Primatol.
  • Behringer, V., Stevens, J., Kivell, T., Neufuss, J., Boesch, C. and Hohmann, G. (2016). Within Arm’s Reach: Measuring Forearm Length to Assess Growth Patterns in Captive Bonobos and Chimpanzees. American Journal of Physical Anthropology [Online] 161:37-43. Available at: http://dx.doi.org/10.1002/ajpa.23004.
    Objectives: Bonobos and chimpanzees are known to differ in various morphological traits, a dichotomy that is sometimes used as an analogy for evolutionary splits during human evolution. The aim of our study was to measure the forearm length of immature and adult bonobos and adult chimpanzees to assess the extent of age–related changes of forearm length in bonobos and sex–dimorphism in bonobos and chimpanzees.

    Materials and methods: As a proxy of somatic growth we measured forearm length of captive bonobos and chimpanzees ranging in age from 1 to 55 years. Measures were taken from subjects inserting their arms into a transparent Plexiglas® tube, a novel technique facilitating repeated measures of nonanesthetized apes in captivity.

    Results:Measures from adult females (>12 years) showed that bonobos exceed chimpanzees in terms of forearm length and that sexual dimorphism in forearm length is pronounced in chimpanzees, but not in bonobos. Forearm length increased significantly with chronological age in bonobos. Validation tests revealed that the device generates useful data on morphometric dimensions.

    Discussion: In most primates, sexual dimorphism in body size is male-biased and the differences in forearm length in chimpanzees follow this trend. Given that males of the two species did not differ in forearm length, the absence/presence of sexual dimorphism of this trait must be due to differences in somatic growth in females. Our novel method offers an alternative to obtain morphometric measures and facilitates longitudinal studies on somatic growth.
  • Kivell, T. (2016). A review of trabecular bone functional adaptation: what have we learned from trabecular analyses in extant hominoids and what can we apply to fossils?. Journal of Anatomy [Online] 228:569-594. Available at: http://dx.doi.org/10.1111/joa.12446.
    Many of the unresolved debates in palaeoanthropology regarding evolution of particular locomotor or manipulative behaviours are founded in differing opinions about the functional significance of the preserved external fossil morphology. However, the plasticity of internal bone morphology, and particularly trabecular bone, allowing it to respond to mechanical loading during life means that it can reveal greater insight into how a bone or joint was used during an individual's lifetime. Analyses of trabecular bone have been commonplace for several decades in a human clinical context. In contrast, the study of trabecular bone as a method for reconstructing joint position, joint loading and ultimately behaviour in extant and fossil non-human primates is comparatively new. Since the initial 2D studies in the late 1970s and 3D analyses in the 1990s, the utility of trabecular bone to reconstruct behaviour in primates has grown to incorporate experimental studies, expanded taxonomic samples and skeletal elements, and improved methodologies. However, this work, in conjunction with research on humans and non-primate mammals, has also revealed the substantial complexity inherent in making functional inferences from variation in trabecular architecture. This review addresses the current understanding of trabecular bone functional adaptation, how it has been applied to hominoids, as well as other primates and, ultimately, how this can be used to better interpret fossil hominoid and hominin morphology. Because the fossil record constrains us to interpreting function largely from bony morphology alone, and typically from isolated bones, analyses of trabecular structure, ideally in conjunction with that of cortical structure and external morphology, can offer the best resource for reconstructing behaviour in the past.

Book section

  • Kivell, T., Lemelin, P., Richmond, B. and Schmitt, D. (2016). Introduction. In: Kivell, T. L., Lemelin, P., Richmond, B. G. and Schmitt, D. eds. The Evolution of the Primate Hand: Anatomical, Developmental, Functional, and Paleontological Evidence. Springer, pp. 1-3. Available at: http://dx.doi.org/10.1007/978-1-4939-3646-5.
  • Kivell, T. (2016). The Primate Wrist. In: Kivell, T. L., Lemelin, P., Richmond, B. G. and Schmitt, D. eds. The Evolution of the Primate Hand: Anatomical, Developmental, Functional, and Paleontological Evidence. Springer. Available at: http://dx.doi.org/10.1007/978-1-4939-3646-5.

Conference or workshop item

  • Dunmore, C., Kivell, T., Stephens, N., Bardo, A., Hublin, J. and Skinner, M. (2019). First metacarpal trabecular morphology: implications for thumb use in great apes and Australopithecus. In: Annual Meeting of the American Association for Physical Anthropologists. Available at: https://physanth.org/annual-meetings/past-meetings/88th-annual-meeting-2019/.
  • Deckers, K., Dunmore, C., Skinner, M. and Kivell, T. (2019). Trabecular ontogeny of African ape third metacarpals. In: Annual Meeting of the American Association for Physical Anthropologists. Available at: https://physanth.org/annual-meetings/past-meetings/88th-annual-meeting-2019/.
  • Tsegai, Z., Skinner, M., Pahr, D., Hublin, J. and Kivell, T. (2018). Trabecular bone ontogeny in the forelimb and hindlimb of chimpanzees. In: European Society for the Study of Human Evolution Meeting.
  • Kivell, T., Dunmore, C., Stephens, N., Spoor, F., Hublin, J. and Skinner, M. (2018). Trabecular bone structure of the Australopithecus afarensis A.L. 438-1 metacarpals and implications for skeletal age and hand use. In: European Society for the Study of Human Evolution Meeting.
  • Dunmore, C., Kivell, T., Pahr, D. and Skinner, M. (2018). Trabecular architecture across the metacarpus reflects different locomotor strategies in hominoids. In: Annual Meeting of the American Association for Physical Anthropologists.
  • Georgiou, L., Kivell, T., Pahr, D. and Skinner, M. (2018). Trabecular bone structure of the distal femur in great apes. In: Annual Meeting of the American Association for Physical Anthropologists.
  • Komza, K., Kivell, T. and Skinner, M. (2018). Unique forms of locomotion in Swartkrans hominins: An analysis of the trabecular structure of the first metatarsal. In: Annual Meeting of the American Association for Physical Anthropologists.
  • Neufuss, J., Robbins, M., Baeumer, J., Humle, T. and Kivell, T. (2017). Comparison of Hand Use and Forelimb Mechanics of Vertical Climbing in Wild Mountain Gorillas and Free-Ranging Chimpanzees. In: 7th European Federation for Primatology Meeting. Available at: https://www.karger.com/Article/PDF/479094.
    Biomechanical analyses of great ape arboreal locomotion in a natural environment are scarce, thus limiting attempts to correlate behavioural and habitat differences with variation in skeletal morphology. Vertical climbing is a crucial locomotor and foraging strategy of great apes and the hands are critically important to maintaining stability on irregular, arboreal substrates. However, little is known about arboreal grips and hand postures, or how these might vary with forelimb posture during vertical climbing on natural substrates of different sizes. This is particularly true of mountain gorillas, which are considered the least arboreal of all African apes and for which the characteristics of vertical climbing have not yet been studied. The aim of this study was to compare temporal kinematics of hand and forelimb use during vertical climbing in wild, habituated mountain gorillas (Gorilla beringei beringei) of the Bwindi Impenetrable Forest (Uganda) and sanctuary chimpanzees (Pan troglodytes) of the Chimfunshi Wildlife Orphanage Trust (Zambia) to assess differences in climbing styles that may relate to variation in hand or forelimb morphology and body mass. We investigated hand and forelimb posture coupled with temporal gait parameters during vertical climbing (both ascent and descent) in 15 mountain gorillas and eight chimpanzees, using video records ad libitum. In both apes, forelimb posture was correlated with substrate size during both ascent and descent climbing. Both apes used power grips and a diagonal power grip, involving three different thumb postures. Gorillas showed greater ulnar deviation of the wrist during climbing than chimpanzees, and the thumb played an important supportive role when vertically descending compliant substrates in gorillas. Comparisons of temporal gait parameters indicated that large-bodied gorillas exhibited significant longer cycle duration, lower stride frequency and generally a higher duty factor than chimpanzees. This study revealed that wild mountain gorillas adapt their climbing strategy to accommodate their large body mass in a similar manner found in captive western lowland gorillas, but that our sanctuary chimpanzees showed less variation in their climbing strategy within a natural environment than has been documented in captive bonobos
  • Dunmore, C., Kivell, T., Pahr, D. and Skinner, M. (2017). Trabecular morphology across the hominoid metacarpus reflects distinct locomotor strategies. In: European Society for the Study of Human Evolution.
  • Stephens, N., Kivell, T., Pahr, D., Hublin, J. and Skinner, M. (2017). Trabecular bone patterning across the human hand: Implications for reconstructing behaviour and manipulation in past populations. In: European Society for the Study of Human Evolution.
  • Arias-Martorell, J., Davenport, R., Kivell, T. and Skinner, M. (2017). Trabecular architecture of the hominoid humerus. In: Annual Meeting of the American Association for Physical Anthropology.

Edited book

  • Kivell, T. (2016). The Evolution of the Primate Hand: Anatomical, Developmental, Functional, and Paleontological Evidence. [Online]. Vol. 589. Kivell, T. L., Lemelin, P., Richmond, B. G. and Schmitt, D. eds. Springer. Available at: http://dx.doi.org/10.1007/978-1-4939-3646-5.
    This book demonstrates how the primate hand combines both primitive and novel morphology, both general function with specialization, and both a remarkable degree of diversity within some clades and yet general similarity across many others. Across the chapters, different authors have addressed a variety of specific questions and provided their perspectives, but all explore the main themes described above to provide an overarching “primitive primate hand” thread to the book. Each chapter provides an in-depth review and critical account of the available literature, a balanced interpretation of the evidence from a variety of perspectives, and prospects for future research questions. In order to make this a useful resource for researchers at all levels, the basic structure of each chapter is the same, so that information can be easily consulted from chapter to chapter. An extensive reference list is provided at the end of each chapter so the reader has additional resources to address more specific questions or to find specific data.

Thesis

  • Komza, K. (2017). A Unique Form of Locomotion in Swartkrans Hominins: An Analysis of the Trabecular Structure of the First Metatarsal.
    Changes in foot bone morphology within the hominin clade are crucial for reconstructing the evolution of bipedalism and a modern human-like gait. Studies of the external morphology of the first metatarsal in humans, non-human apes and fossil hominins, have documented changes in its robusticity, epiphyseal shape and its articulation with the medial cuneiform. Trabecular bone structure has been shown to reflect habitual joint positioning, and as a result offers a promising method of interpreting first metatarsal loading in extant and fossil apes. In this study, microtomography is used to quantify the trabecular structure throughout the head and base of the first metatarsal, of a comparative sample of Homo sapiens (n=11), Pan troglodytes (n=10), Gorilla gorilla (n=10), and Pongo pygmaeus (n=6). Results from these analyses are then applied to two fossil hominin first metatarsals (SKX 5017 and SK 1813), the former being attributed to Paranthropus robustus, and the latter being of unassigned taxonomic status. Results show that within the comparative sample, bone volume fraction (BV/TV) and degree of anisotropy (DA) effectively separate bipedalism from all other forms of locomotion. Specific patterns in anisotropy and trabecular bone density distribution support the hypothesis that higher BV/TV in the dorsal regions of the bone and overall higher DA are reflective of a foot adapted for bipedalism. SKX 5017 shows patterns that are different from all modern taxa, indicating a unique form of bipedalism characterized by a habitually hyperdorsiflexing metatarsophalangeal joint and retained arboreal adaptations. SK 1813 shows a trabecular distribution in the head that is different from SKX 5017 and intermediate between modern human and non-human primates, indicating habitual but less frequent bipedalism than modern Homo sapiens and greater arboreal adaptations than SKX 5017. These results suggest that Swartkrans hominins employed habitual bipedalism, but also displayed a wider range of locomotor behaviour than modern humans.
  • Neufuss, J. (2017). Hand Use and Posture During Manipulative Behaviours and Arboreal Locomotion in African Apes.
    The skill with which primates use their hands to explore and interact with the environment sets them apart from most other mammals. The non-human primate hand serves an important functional role during not only terrestrial and arboreal locomotion, but also enhanced grasping and manipulative behaviours. Understanding how living primates use their hands for these various functions is fundamental for understanding the order Primates and the evolution of humans within this order. While bipedalism and the extraordinary manipulative abilities of our human hand for manufacturing stone tools are considered to be unique, their origins remain controversial. Understanding this evolutionary shift in human hand use from locomotion to manipulation requires comparative studies of hand use in our closest living relatives, the African apes (chimpanzees, bonobos and gorillas). To date, however, little research has been done on African ape daily hand use, including both locomotor and manipulative behaviours, especially in natural environments. This dissertation will address this gap by conducting detailed studies of hand use and posture during two complex manipulative behaviours (i.e., plant-processing, nut-cracking) and arboreal locomotion (i.e., vertical climbing) in the natural environment of African apes.

    I conducted the first comprehensive analysis of bonobo palm oil nut-cracking in a natural environment at the Lola ya Bonobo sanctuary, Democratic Republic of the Congo. All eighteen bonobos showed exclusive laterality for using the hammerstone and there was a significant group-level right-hand bias. The study revealed 15 hand grips for holding differently-sized and -weighted hammerstones, 10 of which had not been previously described in the literature. The findings also demonstrated that bonobos select the most effective hammerstones when nut-cracking and that bonobos, despite rarely using tools in the wild, can be efficient nut-crackers with a skill level that is similar to palm oil nut-cracking chimpanzees of Bossou, Guinea.

    I further provided the first insights into the manual skills of Bwindi mountain gorillas by examining hand-use strategies, hand grips, and hand-preference (i.e., laterality) during the processing of three different plants. Two of these plants are woody-stemmed plants for which the food is more challenging to access in comparison to leaves, lacking physical defenses that are relatively simple to process. Bwindi gorillas used the greatest number of hand actions to process the most complex plant food (i.e., peel-processing) similar to complex thistle feeding by Virunga mountain gorillas. The manipulative actions were ordered in several key stages organised hierarchically. The demands of manipulating natural foods elicited 19 different hand grips and variable thumb postures, of which three grips were new and 16 grips have either been previously reported or show clear similarities to grips used by other wild and captive African apes and humans. A higher degree of lateralisation was elicited for the most complex behaviour of peel-processing but the strength of laterality was only moderate, suggesting that peel-processing is not as complex as thistle leaf-processing by Virunga gorillas.

    Finally, I examined for the first time hand use, forelimb posture and gait chacteristics during vertical climbing in wild, habituated mountain gorillas (Gorilla beringei) of the Bwindi Impenetrable National Park, Uganda, and semi-free-ranging chimpanzees (Pan troglodytes) of the Chimfunshi Wildlife Orphanage Trust, Zambia, both within a natural environment. This research revealed that both apes used power grips and a diagonal power grip, involving three different thumb postures. Gorillas showed greater ulnar deviation of the wrist during climbing than chimpanzees, and the thumb played an important supportive role when vertically descending compliant substrates in gorillas. Comparisons of temporal gait parameters showed that large-bodied gorillas exhibited significant longer cycle duration, lower stride frequency and generally a higher duty factor than chimpanzees. This quantitative analysis revealed that mountain gorillas adapt their climbing strategy to accommodate their large body mass in a similar manner found in captive western lowland gorillas, and that chimpanzees showed less variation in their climbing strategy than has been documented in captive bonobos. In summary, this study demonstrates the importance of forceful hand grips and the variable use of the thumb relative to substrate size in both ape species, and particularly in large-bodied mountain gorillas as they face more biomechanical challenges during vertical climbing than smaller-bodied chimpanzees.

    Together, this dissertation provides new insights into the functional link between hand morphology and behaviour in African apes in their natural environments that may ultimately generate more informed reconstructions of fossil hominin locomotor and manipulative behaviours. Furthermore, this research shows that the suite of "unique human grips" or "unique human manipulative abilities" that have typically defined humans is getting much smaller the more we learn about African apes, particularly in their complex natural environment where the hand has to adjust to varying foods and arboreal substrates, and where individuals have ample opportunity to learn and develop high manipulative skills.
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