Geometric morphometric techniques may offer a promising methodological approach to analyze evolutionary novelties in a quantitative framework. Nevertheless, and despite continuous improvements to this methodology, the inclusion of novel features in these studies presents some difficulties. In the present study, different methods to explicitly include novel traits in geometric morphometric analyses are compared, including homology-free approaches, landmark-based approaches, and combinations of both techniques. The two- ...

Abstract We present a detailed morphological comparative study of the hominin mandible ATE9-1 recovered in 2007 from the Sima del Elefante cave site in Sierra de Atapuerca, Burgos, northern Spain. Paleomagnetic analyses, biostratigraphical studies, and quantitative data obtained through nuclide cosmogenic methods, place this specimen in the Early Pleistocene (1.2–1.3 Ma). This finding, together with archaeological evidence from different European sites, suggests that Western Europe was colonised shortly after the first ...

Here we present a detailed palaeopathological study of the hominin mandible ATE9-1 found at the Sima del Elefante site (TE), Sierra de Atapuerca, Spain. This fossil represents the earliest hominin remains from Western Europe with an age of ca. 1.3 Ma. The specimen displays several dento-gnathic lesions; the antiquity and geographic location of this fossil justifies a detailed palaeopathological study to determine if the pathologies have significantly altered taxonomically relevant features. Our study reveals severe dental ...

Abstract Humans have an unusual life history, with an early weaning age, long childhood, late first reproduction, short interbirth intervals, and long lifespan. In contrast, great apes wean later, reproduce earlier, and have longer intervals between births. Despite 80 y of speculation, the origins of these developmental patterns in Homo sapiens remain unknown. Because they record daily growth during formation, teeth provide important insights, revealing that australopithecines and early Homo had more rapid ontogenies than recent ...

Molar crown morphology varies among primates from relatively simple in some taxa to more complex in others, with such variability having both functional and taxonomic significance. In addition to the primary cusps, crown surface complexity derives from the presence of crests, cuspules, and crenulations. Developmentally, this complexity results from the deposition of an enamel cap over a basement membrane (the morphology of which is preserved as the enamel-dentine junction, or EDJ, in fully formed teeth). However, the relative contribution of the enamel cap and the EDJ to molar crown complexity is poorly characterized. In this study we examine the complexity of the EDJ and enamel surface of a broad sample of primate (including fossil hominin) lower molars through the application of microcomputed tomography and dental topographic analysis. Surface complexity of the EDJ and outer enamel surface (OES) is quantified by first mapping, and then summing, the total number of discrete surface orientation patches. We investigate the relative contribution of the EDJ and enamel cap to crown complexity by assessing the correlation in patch counts between the EDJ and OES within taxa and within individual teeth. We identify three patterns of EDJ/OES complexity which demonstrate that both crown patterning early in development and the subsequent deposition of the enamel cap contribute to overall crown complexity in primates. Am J Phys Anthropol 142:157-163, 2010. © 2010 Wiley-Liss, Inc.

A human lower right deciduous second molar was discovered in 1984 at the entrance of Trou de l'Abîme at Couvin (Belgium). In subsequent years the interpretation of this fossil remained difficult for various reasons: (1) the lack of taxonomically diagnostic elements which would support its attribution to either Homo (sapiens) neanderthalensis or H. s. sapiens; (2) the absence of any reliable chronostratigraphic interpretation of the sedimentary sequence of the site; (3) the contradiction between archaeological interpretations, which attributed the lithic industry to a transitional facies between the Middle and Early Upper Palaeolithic, and the radiocarbon date of 46,820 +/- 3,290 BP obtained from animal bone remains associated with the tooth and the flint tools. Thanks to recent progress regarding these three aspects, the tooth from Trou de l'Abîme may now be studied in detail. Analyses of the morphology and enamel thickness of the fossil yielded diagnostic characters consistent with an attribution to Neandertals. Re-examination of the lithic industry of Couvin shows that it corresponds to the late Middle Palaeolithic rather than a transitional facies. Furthermore, a new analysis of the site stratigraphy indicates that the unit situated above the archaeological layer in which the tooth was found is probably a palaeosol of brown soil type. Comparison with the regional cave sequences as well as with the reference sequence from the Belgian loess belt tends to show that the most recent palaeosol of this type is dated between 42,000 and 40,000 BP. This is consistent with both a recently obtained AMS result at 44,500 BP and the published conventional date.

Les progrès réalisés ces dernières années dans diverses disciplines permettent de réinterpréter la séquence pléistocène du Trou de l'Abîmeà Couvin et les vestiges qui y ont été exhumés. La dent humaine découverte en 1984 peut ainsi être attribuée à l'Homme de Néandertal sur base de l'analyse de sa morphologie et de l'épaisseur de son émail. Le réexamen du matériel archéologique associé à la dent, interprété à l'origine comme relevant de la transition entre le Paléolithique moyen et le Paléolithique supérieur, indique qu'il relève plutôt du Paléolithique moyen. Une nouvelle étude de la faune plaide en faveur d'un apport anthropique. Enfin, une réinterprétation du contexte paléoenvironnemental et chronostratigraphique de la séquence est proposée; l'unité immédiatement sus-jacente à la couche archéologique pourrait être un paléosol qui, par comparaison avec les séquences karstiques et lœssiques régionales, est au plus jeune daté entre 42000 et 40000 BP. Cette nouvelle hypothèse, qui contredit la précédente interprétation qui voyait dans cette partie de la séquence l'équivalent de l'interstade des Cottés (environ 35000 BP), est compatible avec les deux dates C14 provenant de la couche archéologique : une date conventionnelle obtenue dans les années 1980 sur un lot d'ossements (46820 +/- 3290 BP) et une date AMS réalisée en 2008 sur une dent de cheval (44500 +1100/-800 BP). L'étude de la dent de Couvin ne contribue donc que de manière marginale au débat lié à la transition entre Paléolithique moyen et supérieur.

Mandibular corpus form is thought to reflect masticatory function and the size of the dentition, but there is no universal association between crown dimensions and corpus size across anthropoids. Previous research was based on the assumption that crown size is an appropriate proxy for overall tooth size, but this hypothesis remains largely untested. This study assesses the relationship between the volume and surface area of molar crowns and roots by examining two main hypotheses: (1) crown size correlates significantly with root size, and (2) the proportion of root-to-crown surface area is related to dietary proclivity. Permanent M2s (n=58) representing 19 anthropoid species were CT scanned and the volume and surface area of the crown and root were measured. Interspecific correlation and regression analyses reveal significant isometric relationships between crown and root volume and a positive allometric relationship between root and crown surface area (i.e. as crown surface area increases, root surface area becomes disproportionately greater). Intraspecifically, crown and root surface area correlate significantly in some species where such analyses were possible. In general, hard object feeders exhibit relatively larger root surface area per unit crown surface area compared to soft and tough object feeders. The results also show that despite differences in food specialization closely related species have similar root-to-crown surface area proportions, thus indicating a strong phylogenetic influence. Since it is possible that, at least in some species, crown and root size vary independently, future studies should elucidate the relationship between tooth root size and mandible form. Copyright (c) 2009 S. Karger AG, Basel.

Two molars recovered at Trinil, Java, have been the subject of more than a century of debate since their discovery by Eugène Dubois in 1891–92. These molars have been attributed to several ape and human taxa (including Pan and Meganthropus), although most studies agree that they are either fossil Pongo or Homo erectus molars. Complicating the assessment of these molars is the metric and morphological similarity of Pongo and Homo erectus molars, and uncertainty regarding their serial positions within the maxillary row. Here we applied non-destructive conventional and synchrotron microtomographic imaging to measure the structure of these molars and aspects of their development. Comparisons were made with modern Homo and Pongo maxillary molars, as well as small samples of fossil Pongo and Homo erectus molars. Root spread was calculated from three-dimensional surface models, and enamel thickness and enamel-dentine junction morphology were assessed from virtual planes of section. Developmental features were investigated using phase contrast X-ray synchrotron imaging. The highly splayed root morphology of the Trinil maxillary molars suggests that they are not third or fourth molars. Trinil molar enamel thickness is most similar to Homo sapiens and Homo erectus first molar mean values, and is thicker than most modern Pongo molars. The shapes of their enamel-dentine junctions are outside the Pongo range of variation, and within the range of variation in Homo. moreover, the internal long-period line periodicity of these two teeth is most similar to fossil and extant hominins, and is outside of the known range of fossil and living Pongo. Taken together, these results strongly suggest that the two molars are in fact Homo erectus teeth, and Dubois’ original attribution to “Pithecanthropus erectus” (a junior synonym of Homo erectus) is correct.

Developmental and structural afô¨Ånities between modern human and Neanderthal dental remains continue to be a subject of debate as well as their utility for informing assessments of life history and taxonomy. Excavation of the Middle Paleolithic cave site Lakonis in southern Greece has yielded a lower third molar (LKH 1). Here, we detail the crown development and enamel thickness of the distal cusps of the LKH 1 specimen, which has been classiô¨Åed as a Neanderthal based on the presence of an anterior fovea and mid-trigo- nid crest. Crown formation was determined using stand- ard histological techniques, and enamel thickness was measured from a virtual plane of section. Developmental differences include thinner cuspal enamel and a lower periodicity than modern humans. Crown formation in the LKH 1 hypoconid is estimated to be 2.6‚Äì2.7 years, which is shorter than modern human times. The LKH 1 hypoconid also shows a more rapid overall crown exten- sion rate than modern humans. Relative enamel thickness was approximately half that of a modern human sample mean; enamel on the distal cusps of modern human third molars is extremely thick in absolute and relative terms. These ô¨Åndings are consistent with recent studies that demonstrate differences in crown develop- ment, tissue proportions, and enamel thickness between Neanderthals and modern humans. Although overlap in some developmental variables may be found, the results of this and other studies suggest that Neanderthal molars formed in shorter periods of time than modern humans, due in part to thinner enamel and faster crown extension rates.

The thickness of dental enamel is often discussed in paleoanthropological literature, particularly with regard to differences in growth, health, and diet between Neandertals and modern humans. Paleoanthropologists employ enamel thickness in paleodietary and taxonomic studies regarding earlier hominins, but variation in enamel thickness within the genus Homo has not been thoroughly explored despite its potential to discriminate species and its relevance to studies of growth and development. Radiographic two-dimensional studies indicate that Neandertal molar enamel is thin relative to the thick enamel of modern humans, although such methods have limited accuracy. Here we show that, measured via accurate high-resolution microtomographic imaging, Neandertal molar enamel is absolutely and relatively thinner than modern human enamel at most molar positions. However, this difference relates to the ratio of coronal dentine volume to total crown volume, rather than the quantity of enamel per se. The absolute volume of Neandertal molar enamel is similar to that of modern humans, but Neandertal enamel is deposited over a larger volume of coronal dentine, resulting in lower average (and relative) enamel thickness values. Sample sizes do not permit rigorous intragroup comparisons, but Neandertal molar tissue proportions evince less variation than the modern human sample. Differences in three- and two-dimensional enamel thickness data describing Neandertal molars may be explained by dimensional reduction. Although molar tissue proportions distinguish Neanderthals from recent Homo sapiens, additional study is necessary to assess trends in tissue proportions in the genus Homo throughout the Pleistocene.

Thick molar enamel is among the few diagnostic characters of hominins which are measurable in fossil specimens. Despite a long history of study and characterization of Paranthropus molars as relatively 'hyper-thick', only a few tooth fragments and controlled planes of section (designed to be proxies of whole-crown thickness) have been measured. Here, we measure molar enamel thickness in Australopithecus africanus and Paranthropus robustus using accurate microtomographic methods, recording the whole-crown distribution of enamel. Both taxa have relatively thick enamel, but are thinner than previously characterized based on two-dimensional measurements. Three-dimensional measurements show that P. robustus enamel is not hyper-thick, and A. africanus enamel is relatively thinner than that of recent humans. Interspecific differences in the whole-crown distribution of enamel thickness influence cross-sectional measurements such that enamel thickness is exaggerated in two-dimensional sections of A. africanus and P. robustus molars. As such, two-dimensional enamel thickness measurements in australopiths are not reliable proxies for the three-dimensional data they are meant to represent. The three-dimensional distribution of enamel thickness shows different patterns among species, and is more useful for the interpretation of functional adaptations than single summary measures of enamel thickness.

In addition to evidence for bipedality in some fossil taxa, molar enamel thickness is among the few characters distinguishing (thick-enameled) hominins from the (thin-enameled) African apes. Despite the importance of enamel thickness in taxonomic discussions and a long history of scholarship, measurements of enamel thickness are performed almost exclusively on molars, with relatively few studies examining premolars and anterior teeth. This focus on molars has limited the scope of enamel thickness studies (i.e., there exist many fossil hominin incisors, canines, and premolars). Increasing the available sample of teeth from which to compare enamel thickness measurements from the fossil record could substantially increase our understanding of this aspect of dental biology, and perhaps facilitate greater taxonomic resolution of early hominin fossils. In this study, we report absolute and relative (size-scaled) enamel thickness measurements for the complete dentition of modern humans and chimpanzees. In accord with previous studies of molars, chimpanzees show lower relative enamel thickness at each tooth position, with little overlap between the two taxa. A significant trend of increasing enamel thickness from anterior to posterior teeth is apparent in both humans and chimpanzees, indicating that inter-taxon comparisons should be limited to the same tooth position in order to compare homologous structures. As nondestructive imaging techniques become commonplace (facilitating the examination of increasing numbers of fossil specimens), studies may maximize available samples by expanding beyond molars.

Discrete dental traits are used as proxies for biological relatedness among modern human populations and for alpha taxonomy and phylogeny reconstruction within the hominin clade. We present a comparison of the expression of lower molar dental traits (cusp 6, cusp 7, trigonid crest pattern, and protostylid) at the enamel-dentine junction (EDJ) in a variety of extant and fossil hominoid taxa, in order to assess the contribution of the EDJ to the morphology of these traits at the outer enamel surface (OES). Molars (n=44) were imaged nondestructively using high-resolution microCT, and three-dimensional surface models of the EDJ and OES were created to compare trait expression at each surface. Our results indicate that these dental traits originate at the EDJ, and that the EDJ is primarily responsible for their degree of expression at the OES. Importantly, variable trait morphology at the EDJ (often not easily recognizable at the OES) indicates that different developmental processes can produce traits that appear similar at the enamel surface, suggesting caution in intra- and intertaxonomic comparisons. The results also highlight the importance of the EDJ for understanding the morphological development of discrete traits, and for establishing graded scales of variation to compare trait frequency among groups for the purpose of taxonomic and/or phylogenetic analysis. Finally, this study demonstrates that imaging the EDJ of both worn and unworn fossil hominin teeth provides a novel source of information about tooth development and variation in crown morphology.

Absolutely thick molar enamel is consistent with large body size estimates and dietary inferences about Gigantopithecus blacki, which focus on tough or fibrous vegetation. In this study, 10 G. blacki molars demonstrating various stages of attrition were imaged using high-resolution microtomography. Three-dimensional average enamel thickness and relative enamel thickness measurements were recorded on the least worn molars within the sample (n = 2). Seven molars were also virtually sectioned through the mesial cusps and two-dimensional enamel thickness and dentine horn height measurements were recorded. Gigantopithecus has the thickest enamel of any fossil or extant primate in terms of absolute thickness. Relative (size-scaled) measures of enamel thickness, however, support a thick characterization (i.e., not "hyper-thick"); G. blacki relative enamel thickness overlaps slightly with Pongo and completely with Homo. Gigantopithecus blacki dentine horns are relatively short, similar to (but shorter than) those of Pongo, which in turn are shorter than those of humans and African apes. Gigantopithecus blacki molar enamel (and to a lesser extent, that of Pongo pygmaeus) is distributed relatively evenly across the occlusal surface compared with the more complex distribution of enamel thickness in Homo sapiens. The combination of evenly distributed occlusal enamel and relatively short dentine horns in G. blacki results in a flat and low-cusped occlusal surface suitable to grinding tough or fibrous food objects. This suite of molar morphologies is also found to varying degrees in Pongo and Sivapithecus, but not in African apes and humans, and may be diagnostic of subfamily Ponginae.

Molar enamel thickness has played an important role in the taxonomic, phylogenetic, and dietary assessments of fossil primate teeth for nearly 90 years. Despite the frequency with which enamel thickness is discussed in paleoanthropological discourse, methods used to attain information about enamel thickness are destructive and record information from only a single plane of section. Such semidestructive planar methods limit sample sizes and ignore dimensional data that may be culled from the entire length of a tooth. In light of recently developed techniques to investigate enamel thickness in 3D and the frequent use of enamel thickness in dietary and phylogenetic interpretations of living and fossil primates, the study presented here aims to produce and make available to other researchers a database of 3D enamel thickness measurements of primate molars (n=182 molars). The 3D enamel thickness measurements reported here generally agree with 2D studies. Hominoids show a broad range of relative enamel thicknesses, and cercopithecoids have relatively thicker enamel than ceboids, which in turn have relatively thicker enamel than strepsirrhine primates, on average. Past studies performed using 2D sections appear to have accurately diagnosed the 3D relative enamel thickness condition in great apes and humans: Gorilla has the relatively thinnest enamel, Pan has relatively thinner enamel than Pongo, and Homo has the relatively thickest enamel. Although the data set presented here has some taxonomic gaps, it may serve as a useful reference for researchers investigating enamel thickness in fossil taxa and studies of primate gnathic biology.

The evolution of life history (pace of growth and reproduction) was crucial to ancient hominin adaptations. The study of dental development facilitates assessment of growth and development in fossil hominins with greater precision than other skeletal analyses. During tooth formation, biological rhythms manifest in enamel and dentine, creating a permanent record of growth rate and duration. Quantification of these internal and external incremental features yields developmental benchmarks, including ages at crown completion, tooth eruption, and root completion. Molar eruption is correlated with other aspects of life history. Recent evidence for developmental differences between modern humans and Neanderthals remains ambiguous. By measuring tooth formation in the entire dentition of a juvenile Neanderthal from Scladina, Belgium, we show that most teeth formed over a shorter time than in modern humans and that dental initiation and eruption were relatively advanced. By registering manifestations of stress across the dentition, we are able to present a precise chronology of Neanderthal dental development that differs from modern humans. At 8 years of age at death, this juvenile displays a degree of development comparable with modern human children who are several years older. We suggest that age at death in juvenile Neanderthals should not be assessed by comparison with modern human standards, particularly those derived from populations of European origin. Moreover, evidence from the Scladina juvenile and other similarly aged hominins suggests that a prolonged childhood and slow life history are unique to Homo sapiens.

Numerous studies have reported on enamel and dentine development in hominoid molars, although little is known about intraspecific incremental feature variation. Furthermore, a recent histological study suggested that there is little or no time between age at chimpanzee crown completion and age at molar eruption, which is unlikely given that root growth is necessary for tooth eruption. The study presented here redefines growth standards for chimpanzee molar teeth and examines variation in incremental features. The periodicity of Retzius lines in a relatively large sample was found to be 6 or 7 days. The number of Retzius lines and cuspal enamel thickness both vary within a cusp type, among cusps, and among molars, resulting in marked variation in formation time. Daily secretion rate is consistent within analogous cuspal zones (inner, middle, and outer enamel) within and among cusp types and among molar types. Significantly increasing trends are found from inner to outer cuspal enamel (3 to 5 microns/day). Cuspal initiation and completion sequences also vary, although sequences for mandibular molar cusps are more consistent. Cusp-specific formation time ranges from approximately 2 to 3 years, increasing from M1 to M2, and often decreasing from M2 to M3. These times are intermediate between radiographic studies and a previous histological study, although both formation time within cusps and overlap between molars vary considerably. Cusp-specific (coronal) extension rates range from approximately 4 to 9 microns/day, and root extension rates in the first 5 mm of roots range from 3 to 9 microns/day. These rates are greater in M1 than in M2 or M3, and they are greater in mandibular molars than in respective maxillary molars. This significant enlargement of comparative data on nonhuman primate incremental development demonstrates that developmental variation among cusp and molar types should be considered during interpretations and comparisons of small samples of fossil hominins and hominoids.

Modern micro-computed tomography techniques allow the accurate visualization of internal dental structures, and are becoming widely used within (paleo-) anthropological dental studies. There exist several types and name brands of microtomographic systems, however, which have been demonstrated to produce images that vary in resolution and signal-to-noise ratio. As a growing body of dental research using disparate microtomographic techniques is likely to continue accumulating, it is imperative that different systems are compared to ensure that results are comparable and not machine-dependent. In the present study, we compare volume, surface area, and linear measurements recorded on a sample of modern and fossil teeth using four microtomographic systems (three laboratory scanners, and the ID19 beamline of the European Synchrotron Radiation Facility). Results indicate that measurements are comparable between systems (within 3%), but that synchrotron radiation is superior to the other systems because its monochromatic X-rays prevent beam hardening and its parallel beam prevents geometric artifacts in the resultant images, making it easier to record measurements and see fine details at the enamel cervix or dentine horn tips. Although the synchrotron produces higher resolution images with less artifacts, results indicate that for gross morphological measurements (e.g., enamel cap volume, intercuspal distances), each of the scanners produces approximately the same measurements. Combining measurements of teeth from multiple microCT systems presupposes that measurements from each system are comparable; the research presented here indicates that this is the case when teeth are not severely diagenetically remineralized.

The shape of the enamel-dentine junction (EDJ) in primate molars is regarded as a potential indicator of phylogenetic relatedness because it may be morphologically more conservative than the outer enamel surface (OES), and it may preserve vestigial features (e.g., cuspules, accessory ridges, and remnants of cingula) that are not manifest at the OES. Qualitative accounts of dentine-horn morphology occasionally appear in character analyses, but little has been done to quantify EDJ shape in a broad taxonomic sample. In this study, we examine homologous planar sections of maxillary molars to investigate whether measurements describing EDJ morphology reliably group extant anthropoid taxa, and we extend this technique to a small sample of fossil catarrhine molars to assess the utility of these measurements in the classification of fossil teeth. Although certain aspects of the EDJ are variable within a taxon, a taxon-specific cross-sectional EDJ configuration predominates. A discriminant function analysis classified extant taxa successfully, suggesting that EDJ shape may a reliable indicator of phyletic affinity. When considered in conjunction with aspects of molar morphology, such as developmental features and enamel thickness, EDJ shape may be a useful tool for the taxonomic assessment of fossil molars.

Tooth enamel thickness has long been an important character in studies of primate and especially hominin phylogeny, taxonomy, and adaptation. Current methods for accurately assessing enamel thickness involve the physical sectioning of teeth, because measurements of enamel thickness using some radiographic techniques are unreliable. However, because destructive methods limit sample sizes and access to important fossil specimens, it is desirable that they be replaced with nondestructive techniques. Although microfocal X-ray computed tomography (mCT) has been used recently in studies of enamel thickness, the accuracy of this technique has yet to be established. The present research compares physical sections to computer-generated mCT sections of teeth from a variety of primate and nonprimate, recent and fossil taxa to examine whether enamel thickness, tooth size, and diagenetic remineralization (fossilization) impact the ability of mCT to measure enamel thickness accurately. Results indicate that recent teeth of varying size and thickness are clearly and accurately depicted in mCT scans, with measurements from nearly identical planes in physical and mCT sections differing by 3-5%. A fossil papionin molar (ca. 2 Myr) was also accurately measured using mCT scans, although thinner enamel in much older therapsid (ca. 263-241 Myr) teeth could not be distinguished from dentine. mCT is thus an accurate technique for measuring enamel thickness in recent taxa, although heavily mineralized teeth pose an obstacle to the ability of mCT to distinguish dental tissues. Moreover, absolutely thin enamel (less than approximately 0.10 mm) is difficult to resolve adequately in raw mCT images based on pixel values alone. Therefore, caution must be exercised in the application of mCT to the study of fossilized teeth.

This study examines cross-sections of molar crowns in a diverse modern human sample to quantify variation in enamel thickness and enamel-dentine junction (EDJ) shape. Histological sections were generated from molars sectioned buccolingually across mesial cusps. Enamel cap area, dentine area, EDJ length, and bi-cervical diameter were measured on micrographs using a digitizing tablet. Nine landmarks along the EDJ were defined, and X and Y coordinates were digitized in order to quantify EDJ shape. Upper molars show greater values for the components of enamel thickness, leading to significantly greater average enamel thickness than in lower molars. Average enamel thickness increased significantly from M1 to M3 in both molar rows, due to significantly increasing enamel cap area in upper molars, and decreasing dentine area in lower molars. Differences in EDJ shape were found among maxillary molars in combined and individual populations. Sex differences were also found; males showed significantly greater dentine area, EDJ length, and bi-cervical diameters in certain tooth types, which resulted in females having significantly thicker average enamel. Differences in enamel thickness and EDJ shape within molars were also found among populations, although few consistent trends were evident. This study demonstrates that enamel thickness and EDJ shape vary among molars, between sexes, and among populations; these factors must be considered in the categorization and comparison of ape and human molars, particularly when isolated teeth or fossil taxa are included. Human relative enamel thickness encompasses most values reported for fossil apes and humans, suggesting limited taxonomic value when considered alone.

One highly debated issue in palaeoanthropology is that of modern human origins, particularly the issue of when ‘anatomically modern humans’ (AMH) from the African Middle Stone Age became fully modern. While studies of cranial and external dental morphology suggest a modern transition occurred 150000–200000 years ago, little is known about dental development or enamel thickness in AMH.Studies of early members of the genus Homo suggest that the modern, prolonged condition of tooth growth arose late in human evolution, and that the enamel thickness of earlier hominins may not be homologous to the modern condition. This study represents the first integrated investigation of molar crown enamelthickness, volume, and development in fossil hominins, aimed at determining whether differences between AMH and living populations can be detected in these traits. Using high-resolution micro-computed tomography, we demonstrate similarities in enamel thickness and crown volumes between fossil and modern populations. Additionally, long-period growth line numbers and estimates of crown formation times for AMH molars fall within modern human ranges. These findings suggest that tooth structure and growth have remained constant for more than 60000 years, despite the known geographical, technological, and ecological diversity that characterizes later stages of human evolution.

Enamel thickness has figured prominently in discussions of hominid origins for nearly a century, although little is known about its intra-taxon variation. It has been suggested that enamel thickness increases from first to third molars, perhaps due to varying functional demands or developmental constraints, but this has not been tested with appropriate statistical methods. We quantified enamel cap area (c), dentine area (b), and enamel-dentine junction length (e) in coronal planes of sections through the mesial and distal cusps in 57 permanent molars of Pan and 59 of Pongo, and calculated average (c/e) and relative enamel thickness (([c/e]/ radicalb) * 100). Posteriorly increasing or decreasing trends in each variable and average (AET) and relative enamel thickness (RET) were tested among molars in the same row. Differences between maxillary and mandibular analogues and between mesial and distal sections of the same tooth were also examined. In mesial sections of both genera, enamel cap area significantly increased posteriorly, except in Pan maxillary sections. In distal sections of maxillary teeth, trends of decreasing dentine area were significant in both taxa, possibly due to hypocone reduction. Significant increases in AET and RET posteriorly were found in all comparisons, except for AET in Pongo distal maxillary sections. Several significant differences were found between maxillary and mandibular analogues in both taxa. Relative to their mesial counterparts, distal sections showed increased enamel cap area and/or decreased dentine area, and thus increased AET and RET. This study indicates that when AET and RET are calculated from samples of mixed molars, variability is exaggerated due to the lumping of tooth types. To maximize taxonomic discrimination using enamel thickness, tooth type and section plane should be taken into account. Nonetheless, previous findings that African apes have relatively thinner enamel than Pongo is supported for certain molar positions.

The external shape and thickness of the enamel component of primate molars have been employed extensively in phylogenetic studies of primate relationships. The dentine component of the molar crown also has been suggested to be indicative of phylogenetic relationships, but few studies have quantified dentine morphology in order to evaluate this possibility. To explore the utility of dentine shape as an indicator of phylogenetic affinity, a two-dimensional geometric morphometric analysis (EDMA-II) was performed using nine homologous landmarks on a sample of sectioned maxillary molars of extant ceboid, cercopithecoid, and hominoid primates. Results indicate that dentine shape (the configuration of the enamel-dentine junction, or EDJ) can distinguish taxa at every taxonomic level examined, including superfamilies, subfamilies, and closely related genera and species. This supports the idea that dentine morphology may be useful for phylogenetic studies. It is further suggested that the morphology of the EDJ may be more conservative than enamel morphology, and perhaps better-suited to phylogenetic studies. Among the samples studied, cercopithecoid primates have a unique dentine shape, and it is suggested that the development of bilophodont molars may be related to the distinctive EDJ configuration in cercopithecoids.

Many living primates that feed on hard food have been observed to have thick-enameled molars. Among platyrrhine primates, members of the tribe Pitheciini (Cacajao, Chiropotes, and Pithecia) are the most specialized seed and nut predators, and Cebus apella also includes exceptionally hard foods in its diet. To examine the hypothesized relationship between thick enamel and hard-object feeding, we sectioned small samples of molars from the platyrrhine primates Aotus trivergatus, Ateles paniscus, Callicebus moloch, Cebus apella, Cacajao calvus, Chiropotes satanas, Pithecia monachus, and Pithecia pithecia. We measured relative enamel thickness and examined enamel microstructure, paying special attention to the development of prism decussation and its optical manifestation, Hunter-Schreger Bands (HSB). Cebus apella has thick enamel with well-defined but sinuous HSB overlain by a substantial layer of radial prisms. Aotus and Callicebus have thin enamel consisting primarily of radial enamel with no HSB, Ateles has thin enamel with moderately developed HSB and an outer layer of radial prisms, and the thin enamel of the pitheciins (Cacajao, Chiropotes, and Pithecia) has extremely well-defined HSB. Among platyrrhines, two groups that feed on hard objects process these hard foods in different ways. Cebus apella masticates hard and brittle seeds with its thick-enameled cheek teeth. Pitheciin sclerocarpic foragers open hard husks with their canines but chew relatively soft and pliable seeds with their molars. These results reveal that thick enamel per se is not a prerequisite for hard object feeding. The Miocene hominoid Kenyapithecus may have included hard objects in its diet, but its thick-enameled molars indicate that its feeding adaptations differed from those of the pitheciins. The morphology of both the anterior and posterior dentition, including enamel thickness and microstructure, should be taken into consideration when inferring the dietary regime of fossil species.

Studies of dental development have reported conflicting results regarding whether Neanderthal growth and development was similar to that of modern humans. The discovery of a partial permanent maxillary juvenile dentition (OR-1) from the Obi-Rakhmat Grotto, Uzbekistan, provides the opportunity to assess dental development and age at death in a Paleolithic hominin with strong Neanderthal similarities using incremental dental features. Long-period lines on tooth crowns (perikymata) and roots (periradicular bands) were ...

Dental enamel thickness carries precious information about dietary habits and functioning of dentition in fossil species. In the present study we analyzed enamel thickness in ursids, including three fossil taxa: Ursus wenzensis(Early Pliocene), U. deningeri (Middle Pleistocene) and U. spelaeus (Late Pleistocene). Enamel of typical meat-eating carnivorans, artiodactyls, chiropterans and primates was also considered for comparison. Enamel thickness was measured using a planar method, and was scaled by body mass. Analyses showed a clear relationship between the enamel thickness and diet of the bear taxa analyzed. Observed differences in enamel thickness followed a general evolutionary tendency in ursids, relating to the transition from carnivory to omnivory and the increase in tough and abrasive plant products in their diet, especially in cave bears. Among large- bodied ursids, U. spelaeus showed the thickest enamel while U. maritimus was characterized by very thin enamel layer to its body mass, which can be related to its exclusive carnivorous diet. A significant increase in enamel thickness from anterior to posterior teeth was found in U. spelaeus and U. arctos, but not in the domestic dog and U. wenzensis. This is concordant with the progressive increase in the contribution of posterior molars to tough food processing in the evolution of ursids.

Previous histological studies of small samples of chimpanzee and human molars suggested similarities in crown formation time, which is surprising given substantial life history differences. As part of an on-going study of hominoid molar development, we report on the largest-known sample of chimpanzee and human molars, including re-evaluation of previously examined histological sections. Variation of incremental features within and between genera is examined, including Retzius line periodicity, daily secretion rate, and Retzius line number. Differences due to population-level variation and sexual dimorphism are also considered. Significant increasing trends in daily secretion rates were found from inner to outer cuspal enamel, ranging from approximately 3–5 microns/day in chimpanzees. Humans demonstrate slightly lower and higher mean values at the beginning and end of cuspal formation, respectively, but both genera show an overall average of approximately 4 microns/day. Retzius line periodicity ranges from 6–7 days within chimpanzees and 6–12 days within humans. Within upper molars, mesiopalatal cusps (protocones) show thicker cuspal enamel and longer crown formation time than mesiobuccal cusps (paracones). Within lower molars, mesiobuccal cusps (protoconids) show greater Retzius line numbers, longer imbricational formation time, and thicker cuspal enamel than mesiolingual cusps (metaconids), resulting in longer formation times. A negative correlation was found between Retzius line number and periodicity in the human sample, resulting in similar crown formation times within cusp types, despite the range of individual periodic- ities. Few sex differences were found, but a number of developmental differences were apparent among human populations. Cusp-specific formation time in chimpanzees ranges from 2–3 years on average. Within specific cusp types, humans show greater average formation times than chimpanzees, due to higher mean periodicity values and/or thicker cuspal enamel. However, formation time within specific cusp types varies considerably, and the two genera show overlapping ranges, which has implications for the interpretation of small samples.

Phylogenetic, paleodietary, and developmental studies of hominoid primates frequently make use of the post-canine dentition, in particular molar teeth. To study the thickness and shape of molar enamel and dentine, internal dental structures must be revealed (e.g., the location of dentine horn apices), typically necessitating the production of physical sections through teeth. The partially destructive nature of such studies limits sample sizes and access to valuable fossil specimens, which has led scholars to apply several methods of radiographic visualization to the study of teeth. Radiographic methods aimed at visualizing internal dental structures include lateral flat-plane X-rays, ultrasound, terra-hertz imaging, and computed tomography. Each of these techniques has resolution limitations rendering them inadequate for accurately reconstructing both the enamel-dentine junction and the outer enamel surface; the majority of studies are thus performed using physical sections of teeth. A comparatively new imaging technique, micro-computed tomography (mCT), accurately portrays the enamel-dentine junction of primate molars, and provides accurate measurements of enamel cap thickness and morphology. The research presented here describes methodological parameters pertinent to mCT studies of molars (slice thickness and pixel resolution), and the observable impact on measurement accuracy when these parameters are altered. Measurements taken on a small, taxonomically diverse sample of primate molars indicate that slice thickness should be conservatively set at approximately 3.45 % of specimen length, and image resolution should be maximized (ideally, greater than or equal to 2048 √ó 2048 pixels per image) in order to ensure measurement accuracy. After discussing this base-line protocol for future mCT studies of the primate dentition, illustrative applications of this imaging technology are presented.