Portrait of Dr Matthew Skinner

Dr Matthew Skinner

Reader in Biological Anthropology
Deputy Head of School

About

Dr Matthew Skinner is a paleoanthropologist whose research focuses on the analysis of teeth and bones to answer questions about the growth and development, diet, taxonomy and evolutionary history of living and extinct primates, including fossil hominins. Specifically, he is interested in taxonomic diversity and evolutionary history of humans and apes, dental tissue development in the present and past, and form/function relationships in the primate skeleton.

Research interests

  • GRASP  Evolution of the human hand: Grasping trees and tools (funded by European Research Council Starting Grant 2014-2019) 
  • Tooth structure in extant and fossil primates Examination of the two primary tissues of primate teeth, enamel and dentine to 1) improve our understanding of the processes underlying tooth shape, and 2) use tooth structure to contribute to our understanding of the evolutionary history of humans (including our fossil relatives). This research covers the whole period of human evolution and examines fossils from Africa, Europe and Asia.
  • Developmental stress in chimpanzees: Investigating the prevalence and underlying cause of developmental stress in chimpanzees as manifested in their dental tissues.
  • Fossil hominin and hominoid hand use: Comparative investigation of fossil hominin (australopiths to Neandertals) 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. With Tracy Kivell (Kent).
  • Functional signals in trabecular and cortical bone structure: A comparative investigation of internal bony morphology of the primate hand to assess variation in joint loading patterns and how this reflects differences in locomotor and manipulative behaviours. With Tracy Kivell (Kent).

Teaching

Undergraduate

  • SE302: Foundations of Biological Anthropology
  • SE533: Project in Anthropological Science
  • SE541: Paleoanthropology
  • SE567: Methodology in Anthropological Science

Postgraduate

  • SE992: Advanced Topics in Evolutionary Anthropology

Supervision

Dr Skinner can offer supervision of PhD and MA/MSc research within any of his areas of interest – skeletal biology, dental development and morphology, and functional morphology of the postcranial skeleton, including external and internal (using microCT data) bony morphology.

Current 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
  • 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
  • Chris Dunmore: Skeletal form and function of the primate hand
  • Leoni Georgiou: Functional morphology of the hip and knee joints in apes and humans
  • Collin Nathaniel Moore: Premolar root morphology in extant and fossil apes (Max Planck Institute for Evolutionary Anthropology)

Professional

Dr Skinner is available to provide topical comment on or in-depth discussion of topics related to human and primate evolution, the African human fossil record, the function of the human skeleton, and the evolution of teeth.

Publications

Showing 50 of 94 total publications in the Kent Academic Repository. View all publications.

Article

  • Synek, A. et al. (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.
  • Komza, K. and Skinner, M. (2019). First metatarsal trabecular bone structure in extant hominoids and Swartkrans hominins. Journal of Human Evolution [Online] 131:1-21. Available at: https://doi.org/10.1016/j.jhevol.2019.03.003.
    Changes in first metatarsal (MT1) morphology within the hominin clade are crucial for reconstructing the evolution of a forefoot adapted for human-like gait. Studies of the external morphology of the MT1 in humans, non-human apes, and fossil hominins have documented changes in its robusticity, epiphyseal shape and its articulation with the medial cuneiform. Here, we test whether trabecular structure in the MT1 reflects different loading patterns in the forefoot across extant large apes and humans, and within this comparative context, infer locomotor behavior in two fossil hominins from Swartkrans, South Africa. Microtomographic scans were collected from the MT1 of Pongo sp. (n = 6), Gorilla gorilla (n = 10), Pan troglodytes (n = 10), Homo sapiens (n = 11), as well as SKX 5017 (Paranthropus robustus), and SK 1813 (Hominin gen. sp. indet.). Trabecular structure was quantified within the head and base using a ‘whole-epiphysis’ approach with medtool 4.2. We found that modern humans displayed relatively higher bone volume fraction (BV/TV) in the dorsal region of each epiphysis and a higher overall degree of anisotropy (DA), whereas great apes showed higher BV/TV in the plantar regions, reflecting dorsiflexion at the metatarsophalangeal (MTP) joint in the former and plantarflexion in the latter. Both fossils displayed low DA, with SKX 5017 showing a hyper-dorsal concentration of trabecular bone in the head (similar to humans), while SK 1813 showed a more central trabecular distribution not seen in either humans or non-human apes. Additionally, we found differences between non-human apes, modern humans, and the fossil taxa in trabecular spacing (Tb.Sp.), number (Tb.N.), and thickness (Tb.th.). While low DA in both fossils suggests increased mobility of the MT1, differences in their trabecular distributions could indicate variable locomotion in these Pleistocene hominins (recognizing that the juvenile status of SK 1813 is a potential confounding factor). In particular, evidence for consistent loading in hyper-dorsiflexion in SKX 5017 would suggest locomotor behaviors beyond human-like toe off during terrestrial locomotion.
  • Georgiou, L. et al. (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.
  • Zanolli, C. et al. (2019). Evidence for increased hominid diversity in the Early to Middle Pleistocene of Indonesia. Nature Ecology and Evolution [Online] 2019:755-764. Available at: https://doi.org/10.1038/s41559-019-0860-z.
    Since the first discovery of Pithecanthropus (Homo) erectus by E. Dubois at Trinil in 1891, over 200 hominid dentognathic remains have been collected from the Early to Middle Pleistocene deposits of Java, Indonesia, forming the largest palaeoanthropological collection in South East Asia. Most of these fossils are currently attributed to H. erectus. However, because of the substantial morphological and metric variation in the Indonesian assemblage, some robust specimens, such as the partial mandibles Sangiran 5 and Sangiran 6a, were formerly variably allocated to other taxa (Meganthropus palaeojavanicus, Pithecanthropus dubius, Pongo sp.). To resolve the taxonomic uncertainty surrounding these and other contentious Indonesian hominid specimens, we used occlusal fingerprint analysis (OFA) to reconstruct their chewing kinematics; we also used various morphometric approaches based on microtomography to examine the internal dental structures. Our results confirm the presence of Meganthropus as a Pleistocene Indonesian hominid distinct from Pongo, Gigantopithecus and Homo, and further reveal that Dubois’s H. erectus paratype molars from 1891 are not hominin (human lineage), but instead are more likely to belong to Meganthropus.
  • Kupczik, K., Delezene, L. and Skinner, M. (2019). Mandibular molar root and pulp cavity morphology in Homo naledi and other Plio-Pleistocene hominins. Journal of Human Evolution [Online] 130:83-95. Available at: https://dx.doi.org/10.1016/j.jhevol.2019.03.007.
    The craniomandibular morphology of Homo naledi shows variable resemblances with species across Homo, which confounds an easy assessment of its phylogenetic position. In terms of skull shape, H. naledi has its closest affinities with Homo erectus, while mandibular shape places it closer to early Homo. From a tooth crown perspective, the smaller molars of H. naledi make it distinct from early Homo and H. erectus. Here, we compare the mandibular molar root morphology of six H. naledi individuals from the Dinaledi Chamber to those of African and Eurasian Plio-Pleistocene fossil hominins (totalling 183 mandibular first, second and third molars). The analysis of five root metric variables (cervical plane area, root length, root cervix volume, root branch volume, and root surface area) derived from microCT reconstructions reveals that the molar roots of H. naledi are smaller than those of Homo habilis, Homo rudolfensis, and H. erectus, but that they resemble those of three Homo sp. specimens from Swartkrans and Koobi Fora in size and overall appearance. Moreover, though H. naledi molar roots are similar in absolute size to Pleistocene Homo sapiens, they differ from H. sapiens in having a larger root volume for a given cervical plane area and less taurodont roots; the root cervix-to-branch proportions of H. naledi are comparable to those of Australopithecus africanus and species of Paranthropus. Homo naledi also shares a metameric root volume pattern (M2 > M3 > M1) with Australopithecus and Paranthropus but not with any of the other Homo species (M2 > M1 > M3). Our findings therefore concur with previous studies that found that H. naledi shares plesiomorphic features with early Homo, Australopithecus, and Paranthropus. While absolute molar root size aligns H. naledi with Homo from North and South Africa, it is distinguishable from these in terms of root volumetric proportions.
  • Skinner, M. et al. (2019). Growth response of dental tissues to developmental stress in the domestic pig (Sus scrofa). American Journal of Physical Anthropology [Online] 168:764-788. Available at: https://doi.org/10.1002/ajpa.23795.
    Objectives
    To compare relative response of enamel, dentin and bone to developmental stressors between attritional and catastrophic mortality assemblages of pigs.

    Materials and methods
    Heads from 70 Sus scrofa of known sex, weight and age comprising an attritional sample of 50 sick pen (SP) pigs that died prematurely versus 20 control pigs slaughtered at 6 months (Catastrophic assemblage). Hard tissue changes (alveolar bone thinning), abnormal bone formation (Harris lines) and re‐modeling (auditory bullae) were recorded. Areas and volumes of coronal enamel and dentin were recorded from microCT scans with Avizo 6.3 and Geomagic Wrap.

    Results
    Attritional and catastrophic assemblages are metrically indistinguishable. Ages at death and tissue measures in the SP pigs are differentially distributed, necessitating partition into developmental outcome cohorts. SP “late death” pigs are of lesser physiological maturity than expected, free of disease, with large dental tissue dimensions, comparable to “Controls”. SP “early death” pigs have 5% less dentin and enamel and chronic bone infection. Older cohorts of the SP “early deaths” mortality assemblage show progressively reduced enamel. SP pigs show dental evidence of reduced bone mass in the maxilla.

    Discussion
    Bone, dentin and enamel tissues, each, respond distinctively to developmental stressors. Bone mass evinces malnutrition not disease. Both dental tissue reduction and abnormal bone formation link to chronic infection. Paradoxically, reduced dentin mass signals lower survivorship while reduced enamel signals enhanced survivorship. Meaningful comparison of Attritional and Catastrophic assemblages necessitates recognition of developmental outcome cohorts, stratified by age at death and physiological maturity, to reveal heterogeneity of survivorship, tissue measures and lesions.
  • Guatelli-Steinberg, D. et al. (2018). Patterns of lateral enamel growth in Homo naledi as assessed through perikymata distribution and number. Journal of Human Evolution [Online] 121:40-54. Available at: https://doi.org/10.1016/j.jhevol.2018.03.007.
    Perikymata, incremental growth lines visible on tooth enamel surfaces, differ in their distribution and number among hominin species, although with overlapping patterns. This study asks: (1) How does the distribution of perikymata along the lateral enamel surface of Homo naledi anterior teeth compare to that of other hominins? (2) When both perikymata distribution and number are analyzed together, how distinct is H. naledi from other hominins? A total of 19 permanent anterior teeth (incisors and canines) of H. naledi were compared, by tooth type, to permanent anterior teeth of other hominins: Australopithecus afarensis, Australopithecus africanus, Paranthropus robustus, Paranthropus boisei, Homo ergaster/Homo erectus, other early Homo, Neandertals, and modern humans, with varying sample sizes. Repeated measures analyses of the percentage of perikymata per decile of reconstructed crown height yielded several statistically significant differences between H. naledi and other hominins. Canonical variates analysis of percentage of perikymata in the cervical half of the crown together with perikymata number revealed that, in 8 of 19 cases, H. naledi teeth were significantly unlikely to be classified as other hominins, while exhibiting least difference from modern humans (especially southern Africans). In a cross-validated analysis, 68% of the H. naledi teeth were classified as such, while 32% were classified as modern human (most often southern African). Of 313 comparative teeth use for this analysis, only 1.9% were classified as H. naledi. What tends to differentiate H. naledi anterior tooth crowns from those of most other hominins, including some modern humans, is strongly skewed perikymata distributions combined with perikymata numbers that fall in the middle to lower ranges of hominin values. H. naledi therefore tends toward a particular combination of these features that is less often seen in other hominins. Implications of these data for the growth and development of H. naledi anterior teeth are considered.
  • Tsegai, Z. et al. (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.
  • Stephens, N. et al. (2018). Trabecular bone patterning across the human hand. Journal of Human Evolution [Online]. 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.
  • Georgiou, L. et al. (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.
  • Ortiz, A. et al. (2018). Evo-devo models of tooth development and the origin of hominoid molar diversity. Science Advances 4:1-6.
    The detailed anatomical features that characterize fossil hominin molars figure prominently in the reconstruction of
    their taxonomy, phylogeny, and paleobiology. Despite the prominence of molar form in human origins research, the
    underlying developmental mechanisms generating the diversity of tooth crown features remain poorly understood.
    A model of tooth morphogenesis—the patterning cascade model (PCM)—provides a developmental framework to
    explore how and why the varying molar morphologies arose throughout human evolution. We generated virtual
    maps of the inner enamel epithelium—an indelibly preserved record of enamel knot arrangement—in 17 living and
    fossil hominoid species to investigate whether the PCM explains the expression of all major accessory cusps. We
    found that most of the variation and evolutionary changes in hominoid molar morphology followed the general
    developmental rule shared by all mammals, outlined by the PCM. Our results have implications for the accurate
    interpretation of molar crown configuration in hominoid systematics.
  • Tsegai, Z. et al. (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.

    Patterns in Ontogeny of Human Trabecular Bone From SunWatch Village in the Prehistoric Ohio Valley: General Features of Microarchitectural Change | Request PDF. Available from: https://www.researchgate.net/publication/23250866_Patterns_in_Ontogeny_of_Human_Trabecular_Bone_From_SunWatch_Village_in_the_Prehistoric_Ohio_Valley_General_Features_of_Microarchitectural_Change [accessed Jul 25 2018].
  • Kivell, T. et al. (2018). Trabecular architecture and joint loading of the proximal humerus in extant hominoids, Ateles, and Australopithecus africanus. American Journal of Physical Anthropology [Online]. 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.
  • Dunmore, C., Wollny, G. and Skinner, M. (2018). MIA-clustering: a novel method for segmentation of paleontological material. PeerJ [Online]. Available at: http://dx.doi.org/10.7717/peerj.4374.
    Paleontological research increasingly uses high-resolution micro-computed
    tomography (mCT) to study the inner architecture of modern and fossil bone
    material to answer important questions regarding vertebrate evolution. This nondestructive
    method allows for the measurement of otherwise inaccessible
    morphology. Digital measurement is predicated on the accurate segmentation of
    modern or fossilized bone from other structures imaged in mCT scans, as errors in
    segmentation can result in inaccurate calculations of structural parameters. Several
    approaches to image segmentation have been proposed with varying degrees of
    automation, ranging from completely manual segmentation, to the selection
    of input parameters required for computational algorithms. Many of these
    segmentation algorithms provide speed and reproducibility at the cost of flexibility
    that manual segmentation provides. In particular, the segmentation of modern and
    fossil bone in the presence of materials such as desiccated soft tissue, soil matrix
    or precipitated crystalline material can be difficult. Here we present a free opensource
    segmentation algorithm application capable of segmenting modern and fossil
    bone, which also reduces subjective user decisions to a minimum. We compare
    the effectiveness of this algorithm with another leading method by using both
    to measure the parameters of a known dimension reference object, as well as to
    segment an example problematic fossil scan. The results demonstrate that the
    medical image analysis-clustering method produces accurate segmentations and
    offers more flexibility than those of equivalent precision. Its free availability,
    flexibility to deal with non-bone inclusions and limited need for user input give it
    broad applicability in anthropological, anatomical, and paleontological contexts.
  • Hublin, J. et al. (2017). New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens. Nature [Online] 546:289-292. Available at: https://doi.org/10.1038/nature22336.
    Fossil evidence points to an African origin of Homo sapiens from a group called either H. heidelbergensis or H. rhodesiensis. However, the exact place and time of emergence of H. sapiens remain obscure because the fossil record is scarce and the chronological age of many key specimens remains uncertain. In particular, it is unclear whether the present day ‘modern’ morphology rapidly emerged approximately 200 thousand years ago (ka) among earlier representatives of H. sapiens1 or evolved gradually over the last 400 thousand years2. Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315?±?34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established. Furthermore, it shows that the evolutionary processes behind the emergence of H. sapiens involved the whole African continent.
  • Tsegai, Z. et al. (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. et al. (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.
  • Martin, R. et al. (2017). The morphology of the enamel-dentine junction in Neanderthal molars: Gross morphology, non-metric traits, and temporal trends. Journal of Human Evolution [Online] 103:20-44. Available at: http://dx.doi.org/10.1016/j.jhevol.2016.12.004.
    This study explores the morphological differences between the enamel–dentine junction (EDJ) of maxillary and mandibular molars of Neanderthals (n = 150) and recent modern humans (n = 106), and between an earlier Neanderthal sample (consisting of Pre-Eemian and Eemian Neanderthals dating to before 115 ka) and a later Neanderthal sample (consisting of Post-Eemian Neanderthals dating to after 115 ka). The EDJ was visualised by segmenting microtomographic scans of each molar. A geometric morphometric methodology compared the positioning of the dentine horns, the shape of the marginal ridge between the dentine horns, and the shape of the cervix. We also examined the manifestation of non-metric traits at the EDJ including the crista obliqua, cusp 5, and post-paracone tubercle. Furthermore, we report on additional morphological features including centrally placed dentine horn tips and twinned dentine horns. Our results indicate that EDJ morphology can discriminate with a high degree of reliability between Neanderthals and recent modern humans at every molar position, and discriminate between the earlier and the later Neanderthal samples at every molar position, except for the M3 in shape space. The cervix in isolation can also discriminate between Neanderthals and recent modern humans, except at the M3 in form space, and is effective at discriminating between the earlier and the later Neanderthal samples, except at the M2/M2 in form space. In addition to demonstrating the taxonomic valence of the EDJ, our analysis reveals unique manifestations of dental traits in Neanderthals and expanded levels of trait variation that have implications for trait definitions and scoring.
  • Ortiz, A. et al. (2017). Homology, homoplasy and cusp variability at the enamel-dentine junction of hominoid molars. Journal of Anatomy [Online] 231:585-599. Available at: http://dx.doi.org/10.1111/joa.12649.
    Evolutionary studies of mammalian teeth have generally concentrated on the adaptive and functional significance of dental features, whereas the role of development on phenotypic generation and as a source of variation has received comparatively little attention. The present study combines an evolutionary biological framework with state-of-the-art imaging techniques to examine the developmental basis of variation of accessory cusps. Scholars have long used the position and relatedness of cusps to other crown structures as a criterion for differentiating between developmentally homologous and homoplastic features, which can be evaluated with greater accuracy at the enamel–dentine junction (EDJ). Following this approach, we collected digital models of the EDJ and outer enamel surface of more than 1000 hominoid teeth to examine whether cusp 5 of the upper molars (UM C5) and cusps 6 and 7 of the lower molars (LM C6 and LM C7) were associated each with a common developmental origin across species. Results revealed that each of these cusps can develop in a variety of ways, in association with different dental tissues (i.e. oral epithelium, enamel matrix) and dental structures (i.e. from different cusps, crests and cingula). Both within and between species variability in cusp origin was highest in UM C5, followed by LM C7, and finally LM C6. The lack of any species-specific patterns suggests that accessory cusps in hominoids are developmentally homoplastic and that they may not be useful for identifying phylogenetic homology. An important and unanticipated finding of this study was the identification of a new taxonomically informative feature at the EDJ of the upper molars, namely the post-paracone tubercle (PPT). We found that the PPT was nearly ubiquitous in H. neanderthalensis and the small sample of Middle Pleistocene African and European humans (MPAE) examined, differing significantly from the low frequencies observed in all other hominoids, including Pleistocene and recent H. sapiens. We emphasize the utility of the EDJ for human evolutionary studies and demonstrate how features that look similar at the external surface may be the product of different developmental patterns. This study also highlights the importance of incorporating both developmental and morphological data into evolutionary studies in order to gain a better understanding of the evolutionary significance of dental and skeletal features.
  • Skinner, M. and Skinner, M. (2017). Orangutans, enamel defects and developmental health: a comparison of Borneo and Sumatra. American Journal of Primatology [Online] 79:e22668. Available at: http://dx.doi.org/10.1002/ajp.22668.
    Orangutans (Pongo sp.) show among the highest occurrence of three types of developmental enamel defect. Two are attributed to nutritional factors that reduce bone growth in the infant's face early in development. Their timing and prevalence indicate that Sumatra provides a better habitat than does Borneo. The third type, repetitive linear enamel hypoplasia (rLEH) is very common but its etiology is not understood. Our objective is to draw attention to this enigmatic, episodic stressor in the lives of orangutans. We are concerned that neglect of this possible marker of ill health may be contributing, through inaction, to their alarming decline in numbers. Width and depth of an LEH are considered proxies for duration and intensity of stress. The hypothesis that Bornean orangutans would exhibit relatively wider and deeper LEH was tested on 163 independent episodes of LEH from 9 Sumatran and 26 Bornean orangutans measured with a NanoFocus AG “µsurf Mobile Plus” scanner. Non-normally distributed data (depths) were converted to natural logs. No difference was found in width of LEH among the two island taxa; nor are their differences in width or depth between the sexes. After controlling for significant differences in LEH depths between incisors and canines, defects are, contrary to prediction, significantly deeper in Sumatran than Bornean animals (median?=?28, 18?µm, respectively). It is concluded that repetitive LEH records an unknown but significant stressor present in both Sumatra and Borneo, with an average periodicity of 6 months (or multiples thereof) that lasts about 6–8 weeks. It is worse in Sumatra. Given this patterning, shared with apes from a wide range of ecological and temporal sources, rLEH is more likely attributable to disease than to malnutrition.
  • Westaway, K. et al. (2017). An early modern human presence in Sumatra 73,000-63,000 years ago. Nature [Online]:322-325. Available at: http://dx.doi.org/10.1038/nature23452.
  • Evans, A. et al. (2016). A simple rule governs the evolution and development of hominin tooth size. Nature [Online] 530:477-480. Available at: http://www.dx.doi.org/10.1038/nature16972.
    The variation in molar tooth size in humans and our closest relatives (hominins) has strongly influenced our view of human evolution. The reduction in overall size and disproportionate decrease in third molar size have been noted for over a century, and have been attributed to reduced selection for large dentitions owing to changes in diet or the acquisition of cooking1, 2. The systematic pattern of size variation along the tooth row has been described as a ‘morphogenetic gradient’ in mammal, and more specifically hominin, teeth since Butler3 and Dahlberg4. However, the underlying controls of tooth size have not been well understood, with hypotheses ranging from morphogenetic fields3 to the clone theory5. In this study we address the following question: are there rules that govern how hominin tooth size evolves? Here we propose that the inhibitory cascade, an activator–inhibitor mechanism that affects relative tooth size in mammals6, produces the default pattern of tooth sizes for all lower primary postcanine teeth (deciduous premolars and permanent molars) in hominins. This configuration is also equivalent to a morphogenetic gradient, finally pointing to a mechanism that can generate this gradient. The pattern of tooth size remains constant with absolute size in australopiths (including Ardipithecus, Australopithecus and Paranthropus). However, in species of Homo, including modern humans, there is a tight link between tooth proportions and absolute size such that a single developmental parameter can explain both the relative and absolute sizes of primary postcanine teeth. On the basis of the relationship of inhibitory cascade patterning with size, we can use the size at one tooth position to predict the sizes of the remaining four primary postcanine teeth in the row for hominins. Our study provides a development-based expectation to examine the evolution of the unique proportions of human teeth.
  • Couzens, A. et al. (2016). The role of inhibitory dynamics in the loss and reemergence of macropodoid tooth traits. Evolution [Online] 70:568-585. Available at: https://doi.org/10.1111/evo.12866.
    The reversibility of phenotypic evolution is likely to be strongly influenced by the ability of underlying developmental systems to generate ancestral traits. However, few studies have quantitatively linked these developmental dynamics to traits that reevolve. In this study, we assess how changes in the inhibitory cascade, a developmental system that regulates relative tooth size in mammals, influenced the loss and reversals of the posthypocristid, a molar tooth crest, in the kangaroo superfamily Macropodoidea. We find that posthypocristid loss is linked with reduced levels of posterior molar inhibition, potentially driven by selection for lophodont, higher-crowned molar teeth. There is strong support for two posthypocristid reversals, each occurring after more than 15 million years of absence, in large-bodied species of Macropus, and two giant extinct species of short-faced sthenurine kangaroo (Procoptodon). We find that whereas primitive posthypocristid expression is linked to higher levels of posterior molar inhibition, reemergence is tied to a relative increase in third molar size associated with increasing body mass, producing molar phenotypes similar to those in mouse where the ectodysplasin pathway is upregulated. We argue that although shifts in the inhibitory cascade may enable reemergence, dietary ecology may limit the frequency of phylogenetic reversal.
  • Skinner, M. et al. (2016). A dental perspective on the taxonomic affinity of the Balanica mandible (BH-1). Journal of Human Evolution [Online] 93:63-81. Available at: https://doi.org/10.1016/j.jhevol.2016.01.010.
    The Middle Pleistocene represents a period of critical importance in human evolution, marked by encephalisation and dental reduction, and increasing diversification of temporally and spatially distributed hominin lineages in Africa, Asia and Europe. New specimens, especially from areas less well represented in the fossil record, can inform the debate on morphological changes to the skeleton and teeth and the phylogenetic course of human evolution during this period. The mandible from the cave of Mala Balanica, Serbia has recently been re-dated to at least 400 ka, and its well-preserved dentition presents an excellent opportunity to characterize molar crown morphology at this time period, and re-examine claims for a lack of Neandertal affinities in the specimen. In this study we employ microtomography to image the internal structure of the mandibular molars (focusing on the morphology of the enamel-dentine junction, or EDJ) of the BH-1 specimen and a comparative sample (n = 141) of Homo erectus sensu lato, Homo neanderthalensis, Pleistocene Homo sapiens, and recent H. sapiens. We quantitatively assess EDJ morphology using 3D geometric morphometrics and examine the expression of discrete dental traits at the dentine surface. We also compare third molar enamel thickness in BH-1 to those of H. neanderthalensis and both Pleistocene and recent H. sapiens, and document previously unreported morphology of the BH-1 premolar and molar roots. Our results highlight the reliability of the EDJ surface for classifying hominin taxa, indicate a primitive dental morphology for BH-1 molars, and confirm a general lack of derived Neandertal features for the Balanica individual. The plesiomorphic character of BH-1 is consistent with several competing models of Middle Pleistocene hominin evolution and provides an important regional and temporal example for reconstructing morphological changes in the mandible and teeth during this time period.
  • Moore, N. et al. (2016). Premolar root and canal variation in South African Plio-Pleistocene specimens attributed to Australopithecus africanus and Paranthropus robustus. Journal of Human Evolution [Online] 93:46-62. Available at: http://www.dx.doi.org/10.1016/j.jhevol.2015.12.002.
    South African hominin fossils attributed to Australopithecus africanus derive from the cave sites of Makapansgat, Sterkfontein, and Taung, from deposits dated between about 2 and 3 million years ago (Ma), while Paranthropus robustus is known from Drimolen, Kromdraai, and Swartkrans, from deposits dated between about 1 and 2 Ma. Although variation in the premolar root complex has informed taxonomic and phylogenetic hypotheses for these fossil hominin species, traditionally there has been a focus on external root form, number, and position. In this study, we use microtomography to undertake the first comprehensive study of maxillary and mandibular premolar root and canal variation in Australopithecus africanus and Paranthropus robustus (n = 166 teeth) within and between the species. We also test for correlations between premolar size and root morphology as predicted under the ‘size/number continuum’ (SNC) model, which correlates increasing root number with tooth size. Our results demonstrate previously undocumented variation in these two fossil hominin species and highlight taxonomic differences in the presence and frequency of particular root types, qualitative root traits, and tooth size (measured as cervix cross-sectional area). Patterns of tooth size and canal/root number are broadly consistent with the SNC model, however statistically significant support is limited. The implications for hominin taxonomy in light of the increased variation in root morphology documented in this study are discussed.
  • Tsegai, Z. et al. (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.
  • Skinner, M. et al. (2016). An enigmatic hypoplastic defect of the maxillary lateral incisor in recent and fossil orangutans from Sumatra (Pongo abelii) and Borneo (Pongo pygmaeus). International Journal of Primatology [Online]:1-20. Available at: http://dx.doi.org/10.1007/s10764-016-9920-2.

Conference or workshop item

  • Skinner, M. et al. (2017). Premolar root and canal variation in the hominin clade. in: European Society of the Study of Human Evolution.
  • Arias-Martorell, J. et al. (2017). Trabecular architecture of the hominoid humerus. in: Annual Meeting of the American Association for Physical Anthropology.
  • Skinner, M. et al. (2017). Patterns of metameric variation in premolar root morphology in fossil hominins. in: International Symposium on Dental Morphology.
  • Ortiz, A. et al. (2017). Homo or Pongo? Trigon morphology of maxillary molars may solve taxonomic controversies over isolated hominoid teeth from the Asian Pleistocene. in: European Society for the Study of Human Evolution.
  • Delezene, L. et al. (2017). Metric variation in Homo naledi molars. in: Annual Meeting of the American Association for Physical Anthropology.
  • Dunmore, C. et al. (2017). Trabecular morphology across the hominoid metacarpus reflects distinct locomotor strategies. in: European Society for the Study of Human Evolution.
  • Stephens, N. et al. (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.
  • Ortiz, A. et al. (2017). Does the patterning cascade model explain accessory cusp variation in the hominoid clade? in: International Symposium on Dental Morphology.
  • Le Cabec, A., Skinner, M. and Delezene, L. (2017). What can anterior tooth root morphometrics tell us about Homo naledi. in: European Society for the Study of Human Evolution.
  • Brophy, J. et al. (2017). A morphometric assessment of Homo naledi deciduous molar teeth from Dinaledi Chamber, Rising Star cave system, South Africa. in: Annual Meeting of the American Association for Physical Anthropology.
  • Davies, T. et al. (2017). Enamel-dentine junction morphology of hominin mandibular third premolars. in: International Symposium on Dental Morphology.
  • Stephens, N. et al. (2016). Signals of loading and function in the human hand: a multi-method analysis of the external cortical and internal trabecular bone of the metacarpals. in: Annual Meeting of the American Association for Physical Anthropology.
  • Skinner, M. et al. (2016). Enamel-dentine junction morphology and enamel thickness of the Dinaledi dental collection. in: Annual Meeting of the American Association for Physical Anthropology.
  • Daly, E. et al. (2016). A developmental perspective on the postcanine dental proportions of Homo naledi. in: Annual Meeting of the Paleoanthropology Society.
  • Tsegai, Z. et al. (2016). Systemic patterns of trabecular structure in Homo and Pan: Evaluating inter- and intraspecific variability across anatomical sites. in: Annual Meeting of the American Association for Physical Anthropology.
  • Delezene, L. et al. (2016). Metric and nonmetric features of the Homo naledi dentition. in: Annual Meeting of the American Association for Physical Anthropology.
  • Lockey, A. et al. (2016). Upper molar enamel thickness of Plio-Pleistocene hominins. in: European Society for the Study of Human Evolution.
  • Martin, R. and Skinner, M. (2016). History of the study of the enamel-dentine junction and new insights using microtomography. in: Annual Meeting of the American Association for Physical Anthropology.
  • Lockey, A. and Skinner, M. (2016). Enamel thickness in Homo naledi. in: British Association of Biological Anthropology and Osteoarchaeology.
  • de Ruiter, D. et al. (2016). Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa. in: Annual Meeting of the Paleoanthropology Society.
  • Lockwood, V. and Skinner, M. (2016). Morphological variation in posterior femoral entheses in humans, chimpanzees, and gorillas. in: British Association of Biological Anthropology and Osteoarchaeology.
  • Ortiz, A. et al. (2016). Homo or Pongo? Taxonomic discrimination of hominoid upper molars based on the internal surface of the mesial marginal ridge. in: Annual Meeting of the Paleoanthropology Society.

Forthcoming

  • Dunmore, C. et al. (2019). Metacarpal trabecular bone varies with distinct hand-positions used in hominid locomotion. Journal of Anatomy [Online]. 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.
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