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The study of the external tooth morphology can be undertaken in a non-destructive and relatively inexpensive manner. All one needs are good eyes (or a good hand lens), a decent set of calipers and a good single-lens reflex (SLR) or digital camera to keep a permanent record. As such, gross morphology (including size and shape) has long been a subject of interest to paleoanthropologists. Measurements also have a long-standing role in assessing humanevolution (Wolpoff, 1971; Frayer, 1977; Brace et al., 1987; e.g., Bermúdez de Castro and Nicolás, 1996).

In studying the nature of variation and determining the taxonomic composition of a hominin fossil assemblage the phylogenetically closest and thus the most relevant modern comparators are and and following these, and o. Except for , however, modern hominids lack taxonomic diversity, since by most accounts each one is represented by a single living species. is the sister taxon to modern humans and it is represented by two living species. As such the species of have greater relevance for studying interspecific variation in fossil hominin taxonomy. Despite their relatively impoverished species representations and are, nevertheless, represented by subspecies. This makes them relevant for studying the nature of intraspecific variation, in particular for addressing the question of subspecies in hominin taxonomy. The aim of this study is to examine the degree and pattern of molar variation in species and subspecies of and . I test the hypothesis that measurements taken on the occlusal surface of molars are capable of discriminating between species and subspecies in commingled samples of great apes. The results of this study are used to draw inferences about our ability to differentiate between species and subspecies of fossil hominins. The study samples include (n = 152), (n = 64), (n = 79), (n = 208), (n = 61), (n = 30), (n = 140), and (n = 25) . Measurements taken from digital images were used to calculate squared Mahalanobis distances between subspecies pairs. Results indicate that molar metrics are successful in differentiating between the genera, species and subspecies of great apes. There was a hierarchical level of differentiation, with the greatest separation between genera, followed by that between species within the genus and finally between subspecies within species. The patterns of molar differentiation showed excellent concordance with the patterns of molecular differentiation, which suggests that molar metrics have a reasonably strong phylogenetic signal. and were separated by the least dental distance. was separated by a greater distance from these two, but on the whole the distances among subspecies of were less than among subspecies of and . The dental distance between and was greater than that observed between and . With size adjustment intergroup distances between gorilla subspecies were reduced, resulting in distances comparable to subspecies of . A contrast between size-preserved and size-adjusted analyses reveal that size, sexual dimorphism and shape are significant factors in the patterning of molar variation in great apes. The results of this study have several implications for hominin taxonomy, including identifying subspecies among hominins. These implications are discussed.

We have examined the crowns of chimpanzee, australopith, and species and early in order to investigate two different, widely recognized, dental trends in Plio-Pleistocene hominin evolution. They are a reduction in crown size and morphological complexity in , and an increase in crown size and morphological complexity in . A phenetic assessment of maxillary and mandibular molar crown non-metrical traits revealed that two australopith species ( and ) are much more similar to each other than either is to , and together all hominins are distinctively different from chimpanzees ( and ). The difference between and australopith postcanine teeth was 20–30 times greater than that between the australopith species and the difference between the two australopith species was about half the difference between the two extant chimpanzee species. The characters that contribute to the increase in crown complexity seen in do not appear to be primitive retentions from a great ape ancestor, and there is some evidence that the same, or a very similar, trend towards trait intensification is already present in australopiths. These traits include additional cusps on the maxillary and mandibular molars, and the expanded P talonid. Early exhibits the primitive condition for many of the molar traits, but it has also lost many other primitive traits (upper molar anterior and posterior foveae, for example) that are present in the australopiths. Relative to , and similar to the australopiths, early possesses a larger P with a somewhat expanded talonid, but this trend is subsequently reversed in later . Our study reveals that some of the dental trends said to be characteristic of actually appear relatively late in human evolution.

The South African Plio-Pleistocene sites where large numbers of fossil hominid specimens have been discovered in the last 20 years are Sterkfontein, Swartkrans and, most recently, Drimolen. Hominid specimens recovered from these sites have usually been attributed to (from Sterkfontein), (Swartkrans, Drimolen and Sterkfontein) and South African early (Swartkrans, Drimolen and Sterkfontein). We recently started a research project aimed at characterizing cheek teeth cusp morphology of South African Australopithecinae employing digital photographs of their occlusal surfaces. In this paper an analysis of the basic metrical features of maxillary molar cusp areas and proportions of and is presented. We analyzed 92 permanent maxillary molar teeth of South African Australopithecinae. The main results suggest that: a) crown base areas of the three molars are broadly similar in and ; b) significant differences between the two species in relative cusp areas are evident for the protocone of M (with larger than ), the paracone of M, and the protocone of M and M (with larger than ); c) in the total crown area shows the sequence M<M<M as previously described; d) in the sequence observed is M<M>M, as in living apes. This different sequence between and appears to be related mostly to differences in mesial cusp size, which in shows a marked relative expansion from M to M. Also, the variability in absolute cusp areas of the sample seems to be related to the presence of specimens with notably large teeth.

The Sima de los Huesos (SH) and Gran Dolina-TD6 sites in Sierra de Atapuerca (Spain) have each yielded an impressive fossil hominin sample representing Middle Pleistocene and Late Lower Pleistocene European populations, respectively. Paleontological evidence, paleomagnetic analyses, and radiometric dates (U/Th) suggest an interval of 400 to 500 ky for the SH hominins. At Gran Dolina, radiometric dates (ESR and U-series) combined with paleomagnetic analyses and fossil evidence indicate an age range between 780 and 860 ky for the Aurora Stratum of the TD6 level where the fossil hominins were found. We have assigned the SH hominins to the species, whereas the TD6 hominins are representative of , the species named in 1997 (Bermùdez de Castro et al., 1997) to accommodate the variability observed in the TD6 fossil human assemblage. Dental collections of the SH and TD6 sites include more than five hundred deciduous and permanent teeth. The detailed description and morphological comparison of the Atapuerca dental samples will be published elsewhere in a near future, but the examination of an extensive human fossil record, has already revealed some dental characters we consider crucial for phylogenetic studies. We describe those characters and provide an overview of their distribution across the hominin fossil dental record. On the basis of these traits we explore some questions about the phylogenetic relationship between TD6 and SH hominins as well as the evolutionary scenario of these two populations.

Recent studies focusing on dental morphology of extinct and extant human populations have shown, on a global scale, the considerable potential of dental traits as a tool to understand the phenetic relations existing between populations. The aim of this paper is to analyze the dental morphologic relationships between archaic and anatomically modern by means of a new methodology derived from artificial neural networks called Self Organizing Maps (SOMs). The graph obtained by SOMs to some extent recalls a classical Multidimensional Scaling (MDS) or a Principal Component Analysis (PCA) plot. The most important advantages of SOMs is that they can handle vectors with missing components without interpolating missing data. The analyzed database consisted of 1055 Lower-Middle and (Early) Late Pleistocene specimens, which were scored by using dental morphological traits of the Arizona State University Dental Anthropology System (ASUDAS). The principal result indicates a close relationship between the . and Middle Pleistocene specimens and the later Neandertal groups. Furthermore, the dental models of anatomically modern are particularly different compared to the more archaic populations. Thus, SOMs can be considered a valuable tool in the field of dental morphological studies since they enable the analysis of samples at an individual level without any need to interpolate missing data or place individuals in predetermined groups.

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 × 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.

The significance of enamel thickness in hominoid evolution has been plagued by the absence of nondestructive quantitative analysis. The aim of this investigation was to use a nondestructive method of analysis to document the volume of enamel and dentin, thereby providing a quantitative method for comparing both extant and extinct hominoid dentition. High-resolution X-ray computer tomography (HRXCT) is a nondestructive technique for visualizing and quantifying the interior of objects such as bone, teeth and minerals. HRXCT is also capable of obtaining digital information on their 3D geometries and volumetric properties. HRXCT differs from conventional medical CT-scanning in its ability to resolve details as small as a few microns in size, even when imaging objects made of high density materials like enamel and dentin. HRXCT also differs from micro-CT in its ability to examine large specimens up to 1.5 meters, with higher energy sources (typically 125–450 keV) that make the instrument capable of penetrating much denser objects including teeth and very heavily mineralized fossils. HRXCT offers several advantages over both the medical and micro-CT systems. Hominoid teeth used in this study consisted of a collection of extant hominoids as well as a number of fossil hominoids (). HRXCT was used to obtain a data set of serially sectioned digitized images at a slice thickness of approximately 50 micrometers per section. The digital images were analyzed, and 3D reconstructions allowed for the collection of volumetric data for coronal enamel and dentin. HRXCT provides researchers with capabilities not found in other CT systems, which allows for a wider range of specimens sizes, with customizable scanning parameters unique to each specimen type. Our results demonstrate that HRXCT is an effective means by which volumetric data and 3D reconstruction of dental hard tissues are obtained from both extant and extinct hominoid dentitions.

Because of their structural nature, teeth undoubtedly constitute the most abundant fossil evidence for mammal evolution, and are the most investigated elements in paleoanthropology. Recent and ongoing advances in developmental biology, quantitative genetics, and structural microanatomy illustrate the extraordinary amount of information preserved in their tissues (e.g., Dean, 2000; Jernvall and Jung, 2000; Jung et al., 2003; Hlusko, 2004; Mitsiadis and Smith, 2006; Pereira et al., 2006).

Teeth grow incrementally and preserve within them a record of that incremental growth in the form of microscopic growth lines. Studying dental development in extinct and extant primates and its relationship to life history and ecological parameters (e.g., diet, somatic growth rates, gestation length, age at weaning) holds the potential to yield unparalleled insights into the life history profiles of fossil primates. In this paper, we use the incremental growth record preserved in teeth to reconstruct dental development, and thereby infer the life history of , a giant, gorilla-sized, extinct lemur of Madagascar. By examining the microstructure of the first and developing second molars of a juvenile individual, we establish its chronology of molar crown development (M_1 CFT = 1.04 years; M_2 CFT = 1.42 years) and determine its age at death (1.39 years). Crown initiation, formation, and completion times are short compared to . Microstructural data on prenatal M_1 crown formation time allow us to calculate a minimum gestation length of 0.54 years for , compared to 0.70 years in . Postnatal crown and root formation in data allow us to estimate the age at M_1 emergence (∼0.9 years), and to establish a minimum age for M_2 emergence (>1.39 years).If were developmentally similar to large-bodied anthropoids (such as gorillas), we might expect to exhibit slow dental development coupled with relatively early replacement of its deciduous molars. This is not the case. Total molar development is comparatively rapid and poorly explained as a function of adult body mass.