Portrait of Dr Matthew Skinner

Dr Matthew Skinner

Reader in Biological Anthropology

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 our human ancestors (hominins). His current research is focused on taxonomic diversity and evolutionary history of fossil hominins, how teeth grow and how their shape has changed over the course of human evolution, and the influence of behaviour on external and internal bone structure. He is also principal investigator on the European Research Council Consolidator Grant ‘NewHuman’. 

Dr Skinner completed his BA in Archaeology and Biological Anthropology at Simon Fraser University (Canada) and received his PhD in 2008 from The George Washington University (USA). The topic of his doctoral studies was a microtomography-based study of the internal structure of hominin teeth to understand their growth and use in systematics. Matthew was then a postdoctoral fellow (2008-2011) in the Department of Human Evolution in the Max Planck Institute for Evolutionary Anthropology (Germany).

Prior to coming to the University of Kent, Dr Skinner was a Lecturer in the Department of Anthropology at University College London (UK). Matthew has participated in forensic anthropology projects in Canada and East Timor, and palaeontological field projects in France, Germany, Republic of Georgia, Ethiopia, Kenya, South Africa and Indonesia.

Research interests

Dr Matthew Skinner's current research interests include:

  • Origins of the genus Homo, including the evolutionary history of Homo habilis, Homo naledi and Homo floresiensis 
  • Taxonomic diversity in the Pliocene including the genera Australopithecus, Kenyanthropus and Paranthropus 
  • The growth and development of hominin tooth crowns and roots 
  • Internal (trabecular and cortical) bone structure in extant and fossil primate skeletons to better understand the evolution of locomotion and manipulation in hominins 
  • Morphometric analysis of hominin teeth and bones

Projects in which he is involved include the following:

  • NewHuman Pathways to humanity: adaptive niche diversity at the origins of the human lineage [PI: Dr Matthew Skinner, funded by a European Research Council Consolidator Grant 2019-2024. Senior staff and project partners on NewHuman include Professor Tracy Kivell (University of Kent), Professor Dieter Pahr (Vienna University of Technology), Dr Matthew Tocheri (Lakehead University), Professor Lee Berger (University of Witwatersrand) and Professor Jean-Jacques Hublin (Max Planck Institute for Evolutionary Anthropology).] This aim of this project is to reconstruct the behaviour of key fossil hominin species through an examination of the internal structure of their bones and teeth. 
  • GRASP: Evolution of the human hand: grasping trees and tools [PI: Professor Tracy Kivell, Senior Staff Member: Dr Matthew Skinner, funded by European Research Council Starting Grant 2014-2019.] The aim of this project is to understand the evolutionary forces that have influenced hand morphology throughout human evolution. 
  • The dentition of Homo naledi

    Dr Skinner is a primary investigator on the study of the large dental sample of Homo naledi that derives from the Dinaledi and Lesidi Chambers in the Rising Star Cave complex in South Africa. This project is conducted in collaboration with a number of international researchers including, among others, Professor Lee Berger (University of Witwatersrand) and Dr Lucas Delezene (University of Arkansas).
  • 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 hominins. This research covers the whole period of human evolution and examines fossils from Africa, Europe and Asia.
  • Functional signals in hominin bone structure

    A comparative investigation of internal bony morphology of extant and fossil primate skeletons to assess variation in joint loading patterns and how this reflects differences in locomotor and manipulative behaviours.

Teaching

Undergraduate

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

Postgraduate

  • SE992: Advanced Topics in Evolutionary Anthropology
  • SE8011: Advanced Topics in Palaeoanthropology

Supervision

Dr Matthew Skinner can offer supervision of PhD and MA/MSc research within any of his areas of interest – human evolution, skeletal biology, dental development and morphology, and functional morphology of the postcranial skeleton, including external and internal bone morphology.

Postdoctoral researchers

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 (primary 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 (secondary supervisor)
  • Emma Bird: It’s all in the wrist: understanding the evolution of Homo tool-making through internal bone structure (secondary supervisor) 
  • Thomas Davies: A dental perspective on Homo habilis (Max Planck Institute for Evolutionary Anthropoogy) (co-supervisor)

Alumni

  • Christopher Dunmore (PhD in 2019): Skeletal form and function of the primate hand (University of Kent) 
  • Leoni Georgiou (PhD in 2019): Locomotor signals in the trabecular structure of the femur in extant and extinct hominoids (University of Kent) 
  • 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)
  • Collin Nathaniel Moore (PhD in 2016): Premolar root morphology in extant and fossil apes (Max Planck Institute for Evolutionary Anthropology) 

Professional

Research Associate, Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology (Leipzig, Germany) 2013-present. 

Dr Matthew 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 126 total publications in the Kent Academic Repository. View all publications.

Article

  • Skinner, M., Leakey, M., Leakey, L., Manthi, F. and Spoor, F. (2020). Hominin dental remains from the Pliocene localities at Lomekwi, Kenya (1982-2009). Journal of Human Evolution [Online] 145. Available at: https://dx.doi.org/10.1016/j.jhevol.2020.102820.
    Increasing evidence for both taxonomic diversity and early stone manufacture during the Pliocene highlight the importance of the hominin fossil record from this epoch in eastern Africa. Here, we describe dental remains from Lomekwi (West Turkana, Kenya), which date from between 3.2 and 3.5 Ma. The sample was collected between 1982 and 2009 and includes five gnathic specimens and a total of 67 teeth (mostly isolated permanent postcanine teeth). Standard linear dimensions indicate that, while the Lomekwi teeth are relatively small, there is broad overlap in size with contemporary Australopithecus afarensis and Australopithecus deyiremeda specimens at most tooth positions. However, some dental characters differentiate this sample from these species including: a relatively large P4 and M3 compared with the M1, a high incidence of well-developed protostylids and specific accessory molar cuspules. Due to a lack of well-preserved tooth crowns (and the complete absence of mandibular teeth) in the holotype and paratype of Kenyanthropus platyops, and limited comparable gnathic morphology in the new specimens, it cannot be determined whether these Lomekwi specimens should be attributed to this species. Attribution of these specimens is further complicated by a lack of certainty about position along the tooth row of many of the molar specimens. More comprehensive shape analyses of the external and internal morphology of these specimens, and additional fossil finds, would facilitate the taxonomic attribution of specimens in this taxonomically diverse period of human evolution.
  • Hublin, J., Sirakov, N., Aldeias, V., Bailey, S., Bard, E., Delvigne, V., Endarova, E., Fagault, Y., Fewlass, H., Hajdinjak, M., Kromer, B., Krumov, I., Marreiros, J., Martisius, N., Paskulin, L., Sinet-Mathiot, V., Meyer, M., Pääbo, S., Popov, V., Rezek, Z., Sirakova, S., Skinner, M., Smith, G., Spasov, R., Talamo, S., Tuna, T., Wacker, L., Welker, F., Wilcke, A., Zahariev, N., McPherron, S. and Tsanova, T. (2020). Initial Upper Palaeolithic Homo sapiens from Bacho Kiro Cave, Bulgaria. Nature [Online] 581:299-302. Available at: https://doi.org/10.1038/s41586-020-2259-z.
    The Middle to Upper Palaeolithic transition in Europe witnessed the replacement and partial absorption of local Neanderthal populations by Homo sapiens populations of African origin. However, this process probably varied across regions and its details remain largely unknown. In particular, the duration of chronological overlap between the two groups is much debated, as are the implications of this overlap for the nature of the biological and cultural interactions between Neanderthals and H. sapiens. Here we report the discovery and direct dating of human remains found in association with Initial Upper Palaeolithic artefacts, from excavations at Bacho Kiro Cave (Bulgaria). Morphological analysis of a tooth and mitochondrial DNA from several hominin bone fragments, identified through proteomic screening, assign these finds to H. sapiens and link the expansion of Initial Upper Palaeolithic technologies with the spread of H. sapiens into the mid-latitudes of Eurasia before 45 thousand years ago. The excavations yielded a wealth of bone artefacts, including pendants manufactured from cave bear teeth that are reminiscent of those later produced by the last Neanderthals of western Europe. These finds are consistent with models based on the arrival of multiple waves of H. sapiens into Europe coming into contact with declining Neanderthal populations.
  • 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.
  • Lockey, A., Alemseged, Z., Hublin, J. and Skinner, M. (2020). Maxillary molar enamel thickness of Plio-Pleistocene hominins. Journal of Human Evolution [Online] 142. Available at: https://doi.org/10.1016/j.jhevol.2019.102731.
    Enamel thickness remains an important morphological character in hominin systematics and is regularly incorporated into dietary reconstructions in hominin species. We expand upon a previous study of enamel thickness in mandibular molars by examining a large maxillary molar sample of Plio-Pleistocene hominins (n = 62) and a comparative sample of extant nonhuman apes (n = 48) and modern humans (n = 29). 2D mesial planes of section were generated through microtomography, and standard dental tissue variables were measured to calculate average enamel thickness (AET) and relative enamel thickness (RET). AET was also examined across the lingual, occlusal, and buccal regions of the crown. This study confirms previous findings of increasing enamel thickness throughout the Plio-Pleistocene, being thinnest in Australopithecus anamensis and peaking in Australopithecus boisei, with early Homo specimens, exhibiting intermediate enamel thickness. Agreeing with previous findings, 2D plane of section enamel thickness is found to be a poor taxonomic discriminator, with no statistically significant differences observed between fossil hominins. For fossil hominins, modern humans, and Pongo, the occlusal region of enamel was the thickest, and the lingual enamel thickness was greater than buccal. Pan and Gorilla present the opposite pattern with enamel being thinnest occlusally. Comparison at each molar position between the maxilla and mandible revealed very few significant differences in fossil hominins but some evidence of significantly thicker maxillary enamel (AET) in modern humans and thinner maxillary enamel in Pan (RET).
  • 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.
  • Garralda, M., Maureille, B., Le Cabec, A., Oxilia, G., Benazzi, S., Skinner, M., Hublin, J. and Vandermeersch, B. (2020). The Neanderthal teeth from Marillac (Charente, Southwestern France): Morphology, comparisons and paleobiology. Journal of Human Evolution [Online] 138. Available at: https://dx.doi.org/10.1016/j.jhevol.2019.102683.
    Few European sites have yielded human dental remains safely dated to the end of MIS 4/beginning of MIS 3. One of those sites is Marillac (Southwestern France), a collapsed karstic cave where archeological excavations (1967–1980) conducted by B. Vandermeersch unearthed numerous faunal and human remains, as well as a few Mousterian Quina tools. The Marillac sinkhole was occasionally used by humans to process the carcasses of different prey, but there is no evidence for a residential use of the site, nor have any hearths been found. Rare carnivore bones were also discovered, demonstrating that the sinkhole was seasonally used, not only by Neanderthals, but also by predators across several millennia. The lithostratigraphic units containing the human remains were dated to ∼60 kyr. The fossils consisted of numerous fragments of skulls and jaws, isolated teeth and several post-cranial bones, many of them with traces of perimortem manipulations. For those already published, their morphological characteristics and chronostratigraphic context allowed their attribution to Neanderthals. This paper analyzes sixteen unpublished human teeth (fourteen permanent and two deciduous) by investigating the external morphology and metrical variation with respect to other Neanderthal remains and a sample from modern populations. We also investigate their enamel thickness distribution in 2D and 3D, the enamel-dentine junction morphology (using geometric morphometrics) of one molar and two premolars, the roots and the possible expression of taurodontism, as well as pathologies and developmental defects. The anterior tooth use and paramasticatory activities are also discussed. Morphological and structural alterations were found on several teeth, and interpreted in light of human behavior (tooth-pick) and carnivores' actions (partial digestion). The data are interpreted in the context of the available information for the Eurasian Neanderthals.
  • 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.
  • Davies, T., Delezene, L., Gunz, P., Hublin, J. and Skinner, M. (2019). Endostructural morphology in hominoid mandibular third premolars: discrete traits at the enamel-dentine junction. Journal of Human Evolution [Online] 136. Available at: https://doi.org/10.1016/j.jhevol.2019.102670.
    For access to specimens, we would like to thank Bernhard Zipfel, Lee Berger, Sifelani Jira (Evolutionary Studies Intitute, University of the Witwatersrand), Miriam Tawane (Ditsong Museum), Job Kibii (National Museums of Kenya), Metasebia Endalemaw, Yared Assefa (Ethiopian Authority for Research and Conservation of Cultural heritage), Yoel Rak, Alon Barash, Israel Hershkovitz (Sackler School of Medicine), Michel Toussaint (ASBL Archéologie Andennaise, Jean-Jacques Cleyet-Merle (Musée National de Préhistoire des Eyzies-de-Tayac), Ullrich Glasmacher (Institut für Geowissenschaften, Universität Heidelberg), Robert Asher, Hendrik Turni, Irene Mann (Museum für Naturkunde, Berlin), Jakov Radovčić (Croatian Natural History Museum), Christophe Boesch and Uta Schwarz (Max Planck Institute for Evolutionary Anthropology) and the Leipzig University Anatomical Collection (ULAC). For project support we thank Zeresenay Alemseged and Bill Kimbel. We would also like to thank the reviewers, the associate editor and the editor for their helpful comments and guidance, as well as Ottmar Kullmer for comments on an earlier version of this manuscript. This work was funded by the Max Planck Society, and financial support for L.K.D. was provided by a Connor Family Faculty Fellowship and the Office of Research and Development at the University of Arkansas
  • Ortiz, A., Bailey, S., Delgado, M., Zanolli, C., Demeter, F., Bacon, A., Nguyen, T., Nguyen, A., Zhang, Y., Harrison, T., Hublin, J. and Skinner, M. (2019). A distinguishing feature of Pongo upper molars and its implications for the taxonomic identification of isolated hominid teeth from the Pleistocene of Asia. American Journal of Physical Anthropology [Online] 170:595-612. Available at: https://doi.org/10.1002/ajpa.23928.
    The taxonomic status of isolated hominoid teeth from the Asian Pleistocene has long been controversial due to difficulties distinguishing between pongine and hominin molars given their high degree of morphometrical variation and overlap. Here, we combine nonmetric and geometric morphometric data to document a dental pattern that appears to be taxonomically diagnostic among Pongo. We focus on the protoconule, a cuspule of well‐documented evolutionary history, as well as on shape differences of the mesial fovea of the upper molars.
  • Davies, T., Delezene, L., Gunz, P., Hublin, J. and Skinner, M. (2019). Endostructural Morphology in Hominoid Mandibular Third Premolars: Geometric Morphometric Analysis of Dentine Crown Shape. Journal of Human Evolution [Online] 133:198-213. Available at: https://doi.org/10.1016/j.jhevol.2019.06.004.
    In apes, the mandibular third premolar (P3) is adapted for a role in honing the large upper canine. The role of honing was lost early in hominin evolution, releasing the tooth from this functional constraint and allowing it to respond to subsequent changes in masticatory demands. This led to substantial morphological changes, and as such the P3 has featured prominently in systematic analyses of the hominin clade. The application of microtomography has also demonstrated that examination of the enamel-dentine junction (EDJ) increases the taxonomic value of variations in crown morphology. Here we use geometric morphometric techniques to analyze the shape of the P3 EDJ in a broad sample of fossil hominins, modern humans, and extant apes (n = 111). We test the utility of P3 EDJ shape for distinguishing among hominoids, address the affinities of a number of hominin specimens of uncertain taxonomic attribution, and characterize the changes in P3 EDJ morphology across our sample, with particular reference to features relating to canine honing and premolar ‘molarization’. We find that the morphology of the P3 EDJ is useful in taxonomic identification of individual specimens, with a classification accuracy of up to 88%. The P3 EDJ of canine-honing apes displays a tall protoconid, little metaconid development, and an asymmetrical crown shape. Plio-Pleistocene hominin taxa display derived masticatory adaptations at the EDJ, such as the molarized premolars of Australopithecus africanus and Paranthropus, which have well-developed marginal ridges, an enlarged talonid, and a large metaconid. Modern humans and Neanderthals display a tall dentine body and reduced metaconid development, a morphology shared with premolars from Mauer and the Cave of Hearths. Homo naledi displays a P3 EDJ morphology that is unique among our sample; it is quite unlike Middle Pleistocene and recent Homo samples and most closely resembles Australopithecus, Paranthropus and early Homo specimens.
  • 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.
  • 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.
  • Chen, F., Welker, F., Shen, C., Bailey, S., Bergmann, I., Davis, S., Xia, H., Wang, H., Fischer, R., Freidline, S., Yu, T., Skinner, M., Stelzer, S., Dong, G., Fu, Q., Dong, G., Wang, J., Zhang, D. and Hublin, J. (2019). A late Middle Pleistocene Denisovan mandible from the Tibetan Plateau. Nature [Online] 569:409-412. Available at: https://doi.org/10.1038/s41586-019-1139-x.
    Denisovans are members of a hominin group who are currently only known directly from fragmentary fossils, the genomes of which have been studied from a single site, Denisova Cave in Siberia. They are also known indirectly from their genetic legacy through gene flow into several low-altitude East Asian populations and high-altitude modern Tibetans6. The lack of morphologically informative Denisovan fossils hinders our ability to connect geographically and temporally dispersed fossil hominins from Asia and to understand in a coherent manner their relation to recent Asian populations. This includes understanding the genetic adaptation of humans to the high-altitude Tibetan Plateau, which was inherited from the Denisovans. Here we report a Denisovan mandible, identified by ancient protein analysis, found on the Tibetan Plateau in Baishiya Karst Cave, Xiahe, Gansu, China. We determine the mandible to be at least 160 thousand years old through U-series dating of an adhering carbonate matrix. The Xiahe specimen provides direct evidence of the Denisovans outside the Altai Mountains and its analysis unique insights into Denisovan mandibular and dental morphology. Our results indicate that archaic hominins occupied the Tibetan Plateau in the Middle Pleistocene epoch and successfully adapted to high-altitude hypoxic environments long before the regional arrival of modern Homo sapiens.
  • Zanolli, C., Kullmer, O., Kelley, J., Bacon, A., Demeter, F., Dumoncel, J., Fiorenza, L., Grine, F., Hublin, J., Tuan, N., Huong, N., Pan, L., Schillinger, B., Schrenk, F., Skinner, M., Ji, X. and Macchiarelli, R. (2019). Evidence for increased hominid diversity in the Early to Middle Pleistocene of Indonesia. Nature Ecology and Evolution [Online] 3:755-764. 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.
  • Skinner, M., Imbrasas, M., Byra, C. and Skinner, M. (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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Guatelli-Steinberg, D., O’Hara, M., Le Cabec, A., Delezene, L., Reid, D., Skinner, M. and Berger, L. (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.
  • Ortiz, A., Bailey, S., Schwartz, G., Hublin, J. and Skinner, M. (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.
  • 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 (μCT) to study the inner architecture of modern and fossil bone material to answer important questions regarding vertebrate evolution. This non-destructive 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 μCT 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 open-source 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.
  • 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.
  • Skinner, M., Skinner, M., Pilbrow, V. and Hannibal, D. (2017). 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] 37:548-567. Available at: http://dx.doi.org/10.1007/s10764-016-9920-2.
    Developmental dental pathologies provide insight into health of primates during ontogeny, and are particularly useful for elucidating the environment in which extant and extinct primates matured. Our aim is to evaluate whether the prevalence of an unusual dental defect on the mesiolabial enamel of the upper lateral incisor, thought to reflect dental crowding during maturation, is lesser in female orangutans, with their smaller teeth, than in males; and in Sumatran orangutans, from more optimal developmental habitats, than in those from Borneo. Our sample includes 49 Pongo pygmaeus (87 teeth), 21 P. abelii (38 teeth), Late Pleistocene paleo-orangutans from Sumatra and Vietnam (67 teeth), Late Miocene catarrhines Lufengpithecus lufengensis (2 teeth), and Anapithecus hernyaki (7 teeth). Methods include micro-CT scans, radiography, and dental metrics of anterior teeth. We observed fenestration between incisor crypts and marked crowding of unerupted crowns, which could allow tooth-to-tooth contact. Tooth size does not differ significantly in animals with or without the defect, implicating undergrowth of the jaw as the proximate cause of dental crowding and defect presence. Male orangutans from both islands show more defects than do females. The defect is significantly more common in Bornean orangutans (71 %) compared to Sumatran (29 %). Prevalence among fossil forms falls between these extremes, except that all five individual Anapithecus show one or both incisors with the defect. We conclude that maxillary lateral incisor defect is a common developmental pathology of apes that is minimized in optimal habitats and that such evidence can be used to infer habitat quality in extant and fossil apes.
  • Westaway, K., Louys, J., Due Awe, R., Morwood, M., Price, G., Zhao, J., Aubert, M., Joannes-Boyau, R., Smith, T., Skinner, M., Compton, T., Bailey, R., van den Bergh, G., de Vos, J., Pike, A., Stringer, C., Saptomo, E., Rizal, Y., Zaim, J., Santoso, W., Trihascaryo, A., Kinsley, L. and Sulistyanto, B. (2017). An early modern human presence in Sumatra 73,000-63,000 years ago. Nature [Online] 548:322-325. Available at: http://dx.doi.org/10.1038/nature23452.
    Genetic evidence for anatomically modern humans (AMH) out of Africa before 75 thousand years ago (ka) and in island southeast Asia (ISEA) before 60 ka (93–61 ka) predates accepted archaeological records of occupation in the region. Claims that AMH arrived in ISEA before 60 ka have been supported only by equivocal or non-skeletal evidence. AMH evidence from this period is rare and lacks robust chronologies owing to a lack of direct dating applications, poor preservation and/or excavation strategies and questionable taxonomic identifications. Lida Ajer is a Sumatran Pleistocene cave with a rich rainforest fauna associated with fossil human teeth. The importance of the site is unclear owing to unsupported taxonomic identification of these fossils and uncertainties regarding the age of the deposit, therefore it is rarely considered in models of human dispersal. Here we reinvestigate Lida Ajer to identify the teeth confidently and establish a robust chronology using an integrated dating approach. Using enamel–dentine junction morphology, enamel thickness and comparative morphology, we show that the teeth are unequivocally AMH. Luminescence and uranium-series techniques applied to bone-bearing sediments and speleothems, and coupled uranium-series and electron spin resonance dating of mammalian teeth, place modern humans in Sumatra between 73 and 63 ka. This age is consistent with biostratigraphic estimations, palaeoclimate and sea-level reconstructions, and genetic evidence for a pre-60 ka arrival of AMH into ISEA. Lida Ajer represents, to our knowledge, the earliest evidence of rainforest occupation by AMH, and underscores the importance of reassessing the timing and environmental context of the dispersal of modern humans out of Africa.
  • 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.
  • Ortiz, A., Bailey, S., Hublin, J. and Skinner, M. (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.
  • Hublin, J., Ben-Ncer, A., Bailey, S., Freidline, S., Neubauer, S., Skinner, M., Bergmann, I., Le Cabec, A., Benazzi, S., Harvati, K. and Gunz, P. (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.

Conference or workshop item

  • Ortiz, A., Bailey, S., Skinner, M. and Schwartz, G. (2019). Enamel thickness in the deciduous dentition of humans and great apes. In: Annual Meeting of the American Association for Physical Anthropologists. Available at: https://physanth.org/annual-meetings/past-meetings/88th-annual-meeting-2019/.
  • O’Hara, M., Skinner, M. and Guatelli-Steinberg, D. (2019). Comparative two-dimensional relative enamel thickness (RET) of South African hominin premolars. In: Annual Meeting of the American Association for Physical Anthropologists. Available at: https://physanth.org/annual-meetings/past-meetings/88th-annual-meeting-2019/.
  • 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/.
  • Zanolli, C., Skinner, M., Schrenk, F., Hublin, J., Schillinger, B. and Kullmer, O. (2019). The internal structural organization of the post-canine dentition of the initial Early Pleistocene HCRP-U18-501 hominin mandible from Malawi. In: East African Association for Paleoanthropology and Paleontology (EAAPP) Seventh Biennial Conference. Available at: https://eaappinfo.wordpress.com/2019-2/.
  • 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.
  • Zanolli, C., Pan, L., Skinner, M., Dumoncel, J., Beaudet, A., de Beer, F., Hoffman, J., Jakata, K., Macchiarelli, R., Reddy, S., Tawane, M. and Zipfel, B. (2018). What is South African early Homo? New insights from the molar endostructural signature. In: 8th Annual ESHE Meeting - European Society for the Study of Human Evolution. Available at: https://www.eshe.eu/meeting_2018.html#Faro.
  • 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.
  • Skinner, M., Bailey, S., Gunz, P., Kimbel, W., Alemseged, Z., Delezene, L., Menter, C., Moggi-Cecchi, J. and Kupczik, K. (2018). Below the crown: examining interspecies variation in postcanine enamel thickness, EDJ, and root form in the Paranthropus clade. In: Annual Meeting of the American Association for Physical Anthropologists.
    Although there is considerable evidence of shared craniodental morphology within the Paranthropus clade, microwear and isotopic studies suggest that this shared morphology may be linked to different dietary behaviour in eastern and southern Africa. Recently, it has been demonstrated that detailed morphological analyses of the internal structure of tooth crowns (specifically, enamel thickness, enamel-dentine junction morphology and root/pulp canal form), assessed using high resolution microtomography, can reveal previously undetected differences in tooth structure that can have systematic and functional implications In this study, we generate high-resolution surface models of the EDJ surface, external root surface, and pulp canal form of Paranthropus specimens from Kromdraai, Swartkrans, Drimolen, Koobi Fora, West Turkana, and the Omo. We assess enamel thickness in 2D mesial planes of section, root/canal form through an expanded qualitative typology for the hominin clade, and EDJ morphology through landmark-based 3D
    geometric morphometrics. Our results indicate that 1) the generally accepted derived nature of P. boisei relative to P. robustus is matched by detailed morphological features
    of the crown (increased enamel thickness and very low dentine horns) and roots (increased root volumes and increasing distal pulp canal size); 2) there is evidence for population differences between sites preserving P. robustus; and 3) there is evidence at Gondolin (South Africa) for morphological similarity in molar form with P. boisei from
    Koobi Fora. The implications of these findings for the systematics, functional morphology, and paleogeography of Paranthropus are discussed
  • Ortiz, A., Bailey, S., Hublin, J. and Skinner, M. (2018). The morphology of Carabelli’s cusp at the enamel-dentine junction of Australopithecus and Paranthropus upper molars. In: Annual Meeting of the American Association for Physical Anthropologists.
  • Bailey, S., Delezene, L., Moggi-Cecchi, J. and Skinner, M. (2018). Teeth on trial: What can dental morphology really tell us about hominin phylogeny?. In: Annual Meeting of the American Association for Physical Anthropologists.
    Results of studies on cusp homology, experimental studies of dental growth and development and the dental morphology of new fossil hominins like Homo floresiensis and H. naledi force us to re-examine to what extent we can rely on dental morphological data to reconstruct evolutionary relationships. H. floresiensis has primitive deciduous lower canines and primitive permanent lower third and fourth premolars. However, its small, four-cusped lower molars are morphologically derived towards H. sapiens. Rather than indicating a unique phylogenetic link with H. sapiens, it is possible that the simplified molars of H. floresiensis are a result of diminutive tooth size, similar to that seen in the Middle Pleistocene hominins from Sima de los Huesos. But what about the opposite end of the spectrum? The talonid expansion observed in Paranthropus lower deciduous molars and lower permanent premolars and molars has been traditionally understood as derived characters that link P. robustus and P. boisei into a monophyletic clade. However, certain dental morphological characteristics of H. naledi force us to question this interpretation. The permanent lower third premolar and six out of nine deciduous teeth represented by that
    sample show greatest morphological similarity to P. robustus and/or A. africanus (ui1, li2, lc, udm1, ldm1 and ldm2). Yet, a number of other morphological traits are derived towards later Homo (e.g., lack of upper and lower molar accessory cusps) or unique within the hominin clade (upper molar cusp height and spacing). Here we present alternative ways to interpret these conflicting signals.
  • Davies, T., Delezene, L., Hublin, J. and Skinner, M. (2018). Non-metric traits at the enamel-dentine junction of hominoid mandibular third premolars. In: Annual Meeting of the American Association for Physical Anthropologists.
  • 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.
  • Guatelli-Steinberg, D., O’Hara, M., Le Cabec, A., Reid, D., Delezene, L., Skinner, M. and Berger, L. (2018). Patterns of lateral enamel growth in Homo naledi as assessed through perikymata distribution and number. 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.
  • Kupczik, K. and Skinner, M. (2018). Mandibular molar root morphology in Homo naledi. In: Annual Meeting of the American Association for Physical Anthropologists.

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.

Forthcoming

  • Dunmore, C., Wollny, G. and Skinner, M. (2018). MIA-clustering: a novel method for segmentation of paleontological material. PeerJ.
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