Dr Matthew Skinner
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.
- 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).
- SE302: Foundations of Biological Anthropology
- SE533: Project in Anthropological Science
- SE541: Paleoanthropology
- SE567: Methodology in Anthropological Science
- SE992: Advanced Topics in Evolutionary Anthropology
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.
- 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)
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.
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.
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.
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.
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.
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.
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].
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.
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.
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. 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.
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.
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.
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.
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.
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.
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.
De Groote, I. et al. (2016). New genetic and morphological evidence suggests a single hoaxer created 'Piltdown man'. Royal Society open science [Online] 3:160328. Available at: http://dx.doi.org/10.1098/rsos.160328.In 1912, palaeontologist Arthur Smith Woodward and amateur antiquarian and solicitor Charles Dawson announced the discovery of a fossil that supposedly provided a link between apes and humans: Eoanthropus dawsoni (Dawson's dawn man). The publication generated huge interest from scientists and the general public. However, ‘Piltdown man's’ initial celebrity has long been overshadowed by its subsequent infamy as one of the most famous scientific frauds in history. Our re-evaluation of the Piltdown fossils using the latest scientific methods (DNA analyses, high-precision measurements, spectroscopy and virtual anthropology) shows that it is highly likely that a single orang-utan specimen and at least two human specimens were used to create the fake fossils. The modus operandi was found consistent throughout the assemblage (specimens are stained brown, loaded with gravel fragments and restored using filling materials), linking all specimens from the Piltdown I and Piltdown II sites to a single forger—Charles Dawson. Whether Dawson acted alone is uncertain, but his hunger for acclaim may have driven him to risk his reputation and misdirect the course of anthropology for decades. The Piltdown hoax stands as a cautionary tale to scientists not to be led by preconceived ideas, but to use scientific integrity and rigour in the face of novel discoveries.
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.
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.
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.
Stephens, N. et al. (2016). Trabecular architecture in the thumb of Pan and Homo: implications for investigating hand use, loading, and hand preference in the fossil record. American Journal of Physical Anthropology [Online]:1-17. Available at: http://dx.doi.org/10.1002/ajpa.23061.Objectives
Humans display an 85–95% cross-cultural right-hand bias in skilled tasks, which is considered a derived behavior because such a high frequency is not reported in wild non-human primates. Handedness is generally considered to be an evolutionary byproduct of selection for manual dexterity and augmented visuo-cognitive capabilities within the context of complex stone tool manufacture/use. Testing this hypothesis requires an understanding of when appreciable levels of right dominant behavior entered the fossil record. Because bone remodels in vivo, skeletal asymmetries are thought to reflect greater mechanical loading on the dominant side, but incomplete preservation of external morphology and ambiguities about past loading environments complicate interpretations. We test if internal trabecular bone is capable of providing additional information by analyzing the thumb of Homo sapiens and Pan.
Materials and methods
We assess trabecular structure at the distal head and proximal base of paired (left/right) first metacarpals using micro-CT scans of Homo sapiens (n = 14) and Pan (n = 9). Throughout each epiphysis we quantify average and local bone volume fraction (BV/TV), degree of anisotropy (DA), and elastic modulus (E) to address bone volume patterning and directional asymmetry.
We find a right directional asymmetry in H. sapiens consistent with population-level handedness, but also report a left directional asymmetry in Pan that may be the result of postural and/or locomotor loading.
We conclude that trabecular bone is capable of detecting right/left directional asymmetry, but suggest coupling studies of internal structure with analyses of other skeletal elements and cortical bone prior to applications in the fossil record.
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.
Kierdorf, H. et al. (2015). “Missing perikymata”—fact or fiction? A study on chimpanzee (Pan troglodytes verus) canines. American Journal of Physical Anthropology [Online] 157:276-283. Available at: http://dx.doi.org/10.1002/ajpa.22720.Recently, a lower than expected number of perikymata between repetitive furrow-type hypoplastic defects has been reported in chimpanzee canines from the Fongoli site, Senegal (Skinner and Pruetz: Am J Phys Anthropol 149 (2012) 468–482). Based on an observation in a localized enamel fracture surface of a canine of a chimpanzee from the Taï Forest (Ivory Coast), these authors inferred that a nonemergence of striae of Retzius could be the cause for the “missing perikymata” phenomenon in the Fongoli chimpanzees. To check this inference, we analyzed the structure of outer enamel in three chimpanzee canines. The teeth were studied using light-microscopic and scanning-electron microscopic techniques. Our analysis of the specimen upon which Skinner and Pruetz (Am J Phys Anthropol 149 (2012) 468–482) had made their original observation does not support their hypothesis. We demonstrate that the enamel morphology described by them is not caused by a nonemergence of striae of Retzius but can be attributed to structural variations in outer enamel that result in a differential fracture behavior. Although rejecting the presumed existence of nonemergent striae of Retzius, our study provided evidence that, in furrow-type hypoplastic defects, a pronounced tapering of Retzius increments can occur, with the striae of Retzius forming acute angles with the outer enamel surface. We suggest that in such cases the outcrop of some striae of Retzius is essentially unobservable at the enamel surface, causing too low perikymata counts. The pronounced tapering of Retzius increments in outer enamel presumably reflects a mild to moderate disturbance of the function of late secretory ameloblasts.
Conference or workshop item
Skinner, M. et al. (2017). Patterns of metameric variation in premolar root morphology in fossil hominins. in: International Symposium on Dental Morphology.
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.
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.
Arias-Martorell, J. et al. (2017). Trabecular architecture of the hominoid humerus. in: Annual Meeting of the American Association for Physical Anthropology.
Ortiz, A. et al. (2017). Does the patterning cascade model explain accessory cusp variation in the hominoid clade? in: International Symposium on Dental Morphology.
Davies, T. et al. (2017). Enamel-dentine junction morphology of hominin mandibular third premolars. in: International Symposium on Dental Morphology.
Delezene, L. et al. (2017). Metric variation in Homo naledi molars. in: Annual Meeting of the American Association for Physical Anthropology.
Skinner, M. et al. (2017). Premolar root and canal variation in the hominin clade. in: European Society of 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.
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.
Dunmore, C. et al. (2017). Trabecular morphology across the hominoid metacarpus reflects distinct locomotor strategies. in: European Society for the Study of Human Evolution.
Bolter, D. et al. (2016). Assessment of life stages of the individuals at Rising Star. in: Annual Meeting of the American Association for Physical Anthropology.
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.
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. et al. (2016). Upper molar enamel thickness of Plio-Pleistocene hominins. in: European Society for the Study of Human Evolution.
Evans, A. et al. (2016). Evolution of hominin tooth size explained through development‐based models. in: Annual Meeting of the Paleoanthropology Society.
Cofran, Z., Skinner, M. and Walker, C. (2016). Dental development and life history in Homo naledi. in: Annual Meeting of the American Association for Physical Anthropology.
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.
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. 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.
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.
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.
Daly, E. et al. (2016). A developmental perspective on the postcanine dental proportions of Homo naledi. in: Annual Meeting of the Paleoanthropology Society.
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.
Tsegai, Z. et al. (2015). Trabecular bone architecture and distribution in the talus and distal tibia of Homo and Pan. in: Annual Meeting of the European Society for the Study of Human Evolution.