Search

Dental microwear analysis is based on the assumption that a correlation exists between ingested diet and microwear patterns on the enamel surface of teeth, such that diet can be reconstructed by quantifying enamel microwear. Abrasive particles, such as plant phytoliths or silica-based sands incorporated into food items, along with food processing techniques and tooth morphology, are responsible for the microwear features observed. Dental microwear has been extensively studied in both extant and extinct primates, including human populations. The dietary and ecological information that can be derived from dental microwear analyses makes it a technique useful for analyzing non-primate species, such as muskrats, sheep, bats, moles, antelopes, pigs and even dinosaurs. In the attempt to reconstruct species' ecology and diet, microwear research has become a successful procedure. The proliferation and persistence of different methods to quantify microwear patterns require very accurate definitions of microwear variables, since inter-observer error rates cannot be neglected. The use of semiautomatic methods to quantify microwear features does not guarantee low inter-observer error affecting dental microwear results. Error can be caused by taphonomy, microscopy drawbacks of back-scattered electrons, or differences in SEM reproducibility depending on sample shape and orientation. However, fully automatic procedures lack discrimination between ante-mortem and post-mortem wear processes that affect tooth enamel at various degrees, and their application requires experienced control and evaluation. [ABSTRACT FROM AUTHOR]

Functional relationships between diet and tooth morphology form an integral part of paleontological research. The detailed description of occlusal relief and wear patterns of molars provides information about food ingestion and mastication. In early hominids overall molar morphology is fairly similar. Size measurements, such as buccolingual or mesiodistal diameter and 2-D cusp area of hominid molars show considerable overlap. The pioneering works of Butler, Mills, Hiiemae, Kay, Maier and others have shown that the wear pattern on the occlusal surface seems to reflect mastication behavior as an indication of diet. However, most of the interpretations are based on two-dimensional analyses. Occlusal relief measured in 3-D highlights functionally important features useful for quantifying the complex wear patterns on hominid teeth. However, until recently they could not be measured because techniques and methods were lacking. Nevertheless the results of 2-D analyses so far demonstrate that the occlusal surface of teeth records a significant part of the life history of an individual. The 3-D analysis of wear patterns on hominid teeth may provide additional information regarding the relationships between diet, chewing behavior and early hominid evolution. In this case study we employ a new 3-D approach to compare details on the occlusal surface of worn molars of Australopithecus afarensis, Australopithecus africanus and Paranthropus robustus in order to examine possible differences in tooth wear patterns. High resolution optical topometry enables us to measure parameters on 3-D computer models of teeth. Here, we compare various occlusal morphologies of worn lower second molars and attempt to interpret function, taking dental and masticatory principles into account. Our results indicate that diverse modes of occlusal wear in Australopithecus and Paranthropus are evident. A closer look at the occlusal relief and wear facet pattern shows that an assortment of mechanisms for crushing, shearing and grinding on a single tooth are common, since orientation and inclination of wear facets vary. The fact that A. afarensis molars show diverse functional areas with little variation among individuals suggests it had a dental toolkit to cope with a wide range of food qualities and may indicate a species-specific dietary spectrum. A. africanus and P. robustus molars, with their pronounced and relatively rapid flattening of crown relief and diverse individual wear patterns, point towards hard-object feeding and greater intraspecific variation in diet. P. robustus, however, with somewhat higher occlusal relief, can be interpreted as an omnivorous generalist with hard objects as fall-back foods. [ABSTRACT FROM AUTHOR]

Fifty years ago, investigators realized they could gain insights into jaw movement and tooth-use through light-microscope analyses of wear patterns on teeth. Since then, numerous analyses of modern and fossil material have yielded insights into the evolution of tooth use and diet in a wide variety of animals. However, analyses of fossils and archeological material are ultimately dependent on data from three sources, museum samples of modern animals, living animals (in the wild or in the lab), and in vitro studies of microwear formation. These analyses are not without their problems. Thus, we are only beginning to get a clearer picture of the dental microwear of the early hominins. Initial work suggested qualitative differences in dental microwear between early hominids, but it wasn't until Grine's analyses of the South African australopithecines that we began to see quantitative, statistical evidence of such differences. Recent analyses have (1) reaffirmed earlier suggestions that Australopithecus afarensis shows microwear patterns indistinguishable from those of the modern gorilla, and (2) shown that the earliest members of our genus may also be distinguishable from each other on the basis of their molar microwear patterns. While this work hints at the possibilities of moving beyond standard evolutionary-morphological inferences, into inferences of actual differences in tooth use, we still know far too little about the causes of specific microwear patterns, and we know surprisingly little about variations in dental microwear patterns (e.g., between sexes, populations, and species). In the face of such challenges, SEM-analyses may be reaching the limits of their usefulness. Thus, two methods are beginning to catch attention as possible ‘‘next steps'' in the evolution of dental microwear analyses. One technique involves a return to lower magnification analyses, using qualitative assessments of microwear patterns viewed under a light microscope. The advantages of these analyses are that they are cheap and fast, and may easily distinguish animals with extremely different diets. The disadvantages are that they are still subjective and may not be able to detect subtle dietary differences or artifacts on tooth surfaces. Another technique involves the use of scale-sensitive fractal analyses of data from a confocal microscope. Advantages include the ability to quickly and objectively characterize wear surfaces in 3D over entire wear facets. The main disadvantage lies in the newness of the technique and challenges imposed by developing such cutting edge technology. With the development of new approaches, we may be able to take dental microwear analyses to a new level of inference. [ABSTRACT FROM AUTHOR]

Dental functional morphology can inform us on the dietaryadaptations of early hominins and other fossil primates. Traditionalapproaches to understanding dental form-function relationships haverelied mostly on unworn teeth for analysis. This has limited oursamples and our understanding of how teeth are adapted to wear in amanner that keeps them mechanically efficient for chewing. Thispaper reviews a relatively new tool for the study of occlusalfunctional morphology, dental topographic analysis. Thislandmark-free, three-dimensional approach involves the creation andmeasurement of digital models of teeth using point cloud data andGeographic Information Systems software. Three examples arepresented. First, a study of living great apes is reviewed to showthat worn teeth can be included in the study of dental topography,and that species with different diets have corresponding andpredictable differences in the shapes of their molars at comparablestages of tooth wear. Second, a longitudinal study of howlingmonkeys is summarized to demonstrate that different individualswithin this species have consistent changes in crown shape as theirteeth wear down. This suggests species-specific wear patterns, anecessary prerequisite for the inference of function from form ofworn fossil teeth. Third, a new dental topographic analysis ispresented for Australopithecus africanus and Paranthropusrobustus to illustrate that this approach can offer insights intothe dietary adaptations of early hominins and other fossil primates.Results presented here confirm that the A. africanus and P. robustus differed in their dietary adaptations. The degree ofdifference between their occlusal morphologies is on the orderexpected of species that often eat similar foods, but differ at "crunch" times. Dental topography data suggest that P.robustus probably fell back more on hard, brittle items whereasA. africanus relied on tougher, more elastic foods when preferred resources were less available. [ABSTRACT FROM AUTHOR]

Analysis of human tooth enamel using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) provides a basis for systematic evaluation of variation in the chemical composition of enamel in relation to tooth crown geometry. Analysis of thin sections allows a sampling strategy that can be cross-referenced to incremental growth structures in tooth enamel. Strontium and calcium are incorporated into developing teeth in a manner that reflects changing physiological concentrations in the body. Strontium/calcium (Sr/Ca) ratios are expected to decease at birth in breastfed infants, because the mammary gland exerts a greater activating effect on calcium transfer than the placenta. However, Sr/Ca ratios should increase at birth in infants fed on a formula derived from cow's milk. Changes in Sr/Ca ratios across the neonatal line in five out of six deciduous teeth from children of known mode of feeding within the first few months after birth conform to the predicted direction of change, indicating that changes in physiological concentrations of strontium and calcium resulting from a dietary shift during the secretory stage of enamel formation may not be completely overwhelmed during enamel maturation. Implications for the reconstruction of longitudinal records of infant diet from tooth enamel are discussed. [ABSTRACT FROM AUTHOR]

All hominid molars show the same sequence of cusp initiation, but differ in the later stages of development. The topography of the dentin-enamel junction (DEJ) represents the outcome of differential growth between cusps. Since the cusps grow in an orderly sequence from tip to base (defined by the plane of coalescence with adjacent cusps), quantification of cusp volume and relationships can be used to reconstruct successive stages in development and their contribution to the morphometry of the crown surface. Their volume and spatial relationships at the DEJ enable us to partition cell proliferation in relation to cusp initiation, while quantification of the amount and distrib ution of enamel overlying the DEJ provides the necessary discrimination between cell proliferation and cell function, expressed in enamel matrix apposition. We have developed a three-dimensional computerized model of a lower molar tooth that enables us to identify and quantify the different stages of tooth development defined above. The model is based on serial micro-computed tomography (microCT) images of human teeth that provide accurate quantification of the outer and inner enamel and dentin boundaries of individual cusps. We have used this model to compare morphogenesis in the lower second deciduous molar and lower first permanent molar. Spatial relationships of the cusps, expressed by the topography of the DEJ showed that shape differences were established in the early stages of morphogenesis by differential proliferation within the developing tooth germ and that cusp size and proportions were modified at the crown surface by enamel apposition. Reduction of the hypoconulid in the permanent molar shown at the DEJ was largely masked by the exceptional thickness of enamel on this cusp. We propose that this model provides a novel contribution to the identification of ontogenetic trajectories and their contribution to evolutionary trends in tooth size, shape and enamel thickness. [ABSTRACT FROM AUTHOR]

Reported here are the preliminary results of an ongoing study undertaken to determine if there are significant changes from the results obtained in the middle of the 20th Century in the range of variation in dental development in American children of European and African ancestry. Several thousand orthopanoramic radiographs, available from the Dental Clinics of Temple University and the University of Pennsylvania, in Philadelphia, Pennsylvania will eventually be incorporated into this study. The 170 radiographs that have thus far been analyzed document significant changes in the maturation and development of the first and second permanent lower molars. Children in this study have dentitions that are maturing earlier than those in the samples published by Moorrees et al.(1963)and (1973). If the results of this preliminary analysis are confirmed by the incorporation of additional teeth and a larger sample of children, as has been reported elsewhere, it will be necessary to reconsider the characterization of dental development in living humans. Confirmation would also require re-evaluation of the range of inherent plasticity in human dental development. These preliminary results, along with the work by zihlman et.al (2004), suggest that current concepts of what constitutes ‘‘normal'' dental development in living humans and chimpanzees may have to be reconsidered; there are also marked implications for the way in which the developing dentition in fossil hominins is characterized. [ABSTRACT FROM AUTHOR]

The present paper describes a novel analytical approach to provide a comprehensive description of the complex interactions that exist between the growing permanent mandibular teeth (excluding the third molars), and to quantify variability in sequences of key events during crown and root formation, independent of chronological age. Importantly, our method integrates the fundamental concept of modularity and rejects the old statistical fallacy of analyzing data on the assumption that it contains no information beyond that revealed on a tooth-by- tooth analysis. Indeed, interactions between growing teeth may also contain some information, which enables developmental or evolutionary information to be uncovered. Our training sample is based upon cross-sectional standardized panoramic radiographs of the teeth of a total of 2089 children (1206 girls and 883 boys) of different geographic origins (mainly Western Europe, Southern Iran, and Ivory Coast). We observe that, in extant humans sampled so far, the relative development of the permanent incisors is more plastic and varies more than for other teeth. Therefore, we consider that the quantification of possible variations between onsets, durations and rates of development of different teeth in any given child, within a large sample, is a prerequisite to the analysis of fossil hominids. In particular, we seriously question the assumption that the anterior teeth can serve as a reliable substitute for the other permanent teeth, and in particular for interpretations on somatic maturity and brain size. Our hypothesis of modularity in dental development and our method derived from this concept can serve as a basis for identifying and studying patterns of dental growth and, importantly, for comparisons between extant populations, and/or fossil species. These studies do not need to be hedged with age assessments of unknown accuracy and reliability levels (particularly in fossils), or the assumption of independence between growing teeth. [ABSTRACT FROM AUTHOR]

We present preliminary results from quantitative genetic analyses of tooth size variation in two outbred pedigreed populations, baboons and mice. These analyses were designed to test the dental field theory as proposed by Butler (1939), that there are three fields within the dentition: incisor, canine, and molar. Specifically we estimated the genetic correlation between pairs of linear size measurements. Results from the baboon analyses suggest that there may also be a premolar field that is only partially independent of the molar field proposed by Butler (1939). Analyses of the mouse data indicate that for mice, size variation in the incisors appears to be genetically independent of molar size. If the field theory is correct, future analyses on incisor data for the baboons will return similar results of genetic independence. Circumstantial evidence from the fossil record suggests that there will be at least some degree of independence between the anterior and postcanine dentitions of primates. [ABSTRACT FROM AUTHOR]

Aspects of imbricational enamel growth are important for two reasons. First, they may be species-typical, providing insight into taxonomic questions. Second, because dental and somatic growth are linked, aspects of imbricational enamel growth may also provide insights into species-typical rates of growth and development. The present study investigates aspects of imbricational enamel formation in Neandertal anterior teeth relative to three modern human population samples from diverse regions (Point Hope, Alaska; Newcastle-upon-Tyne, England; Southern Africa). A recent study by the same authors (Guatelli-Steinberg et al., 2005) focuses on evaluating how different Neandertals were from these modern human populations in the number of [ABSTRACT FROM AUTHOR]

The study of hominid enamel microanatomical features is usually restricted to the examination of fortuitous enamel fractures by low magnification stereo-zoom microscopy or, rarely, because of its intrusive nature, by high magnification compound microscopy of ground thin sections. To contend with limitations of magnification and specimen preparation, a Portable Confocal Scanning Optical Microscope (PCSOM) has been specifically developed for the non-contact and non-destructive imaging of early hominid hard tissue microanatomy. This unique instrument can be used for high resolution imaging of both the external features of enamel, such as perikymata and microwear, as well as internal structures, such as cross striations and striae of Retzius, from naturally fractured or worn enamel surfaces. Because there is veritably no specimen size or shape that cannot be imaged (e.g. fractured enamel surfaces on intact cranial remains), study samples may also be increased over what would have been possible before. We have applied this innovative technology to the study of enamel microanatomical features from naturally occurring occluso-cervical fractures of the South African hominid, Australopithecus africanus representing different tooth types. We present for the first time detailed information regarding cross striation periodicity for this species and, in addition, we present data on striae-EDJ angles in a large sample of teeth and crown formation time for a molar of A. africanus. Our results characterize a pattern of enamel development for A. africanus, which is different to that reported for the genus Paranthropus, as previously observed. [ABSTRACT FROM AUTHOR]

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 periodicities. 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. [ABSTRACT FROM AUTHOR]

Work based on ground sections of teeth has provided accurate information on dental development in extant and extinct hominoid species. In contrast to radiographic studies, histological work is usually carried out using relatively small sample sizes. However, incremental lines in enamel and dentine enable us to interpret stages of crown formation and to establish patterns of dental development. Although these types of studies have been carried out in modern humans, common chimpanzees, gorillas, orangutans, and gibbons as well as in some extinct hominoids, almost nothing is known about the bonobo (Pan paniscus). In this paper we present some aspects of dental development for a young female with the I1 crown just completed. Ground sections were obtained for the right I1 and M1. The spacing between successive cross striations was measured in the outer, middle and inner portions of occlusal, lateral and cervical thirds of the enamel. The periodicities of the striae of Retzius were obtained, and the number of striae/perikymata were used to calculate the lateral formation time. Prism length and the average distance between cross striations were used to determine the cuspal formation time. Spacing between cross striations shows a gradual increase from the inner to the outer portions, and a decrease from the occlusal to the cervical region, as observed in modern humans and great apes. It is noteworthy that average values in this P. paniscus individual appear to be high. Crown formation time of this P. paniscus I1 was short. In addition, the perikymata packing pattern in P. paniscus was also different from that of G. gorilla and P. troglodytes, in that the number of perikymata increased towards the cervix. [ABSTRACT FROM AUTHOR]

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 Megaladapis edwardsi, 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 Gorilla. Microstructural data on prenatal M_1 crown formation time allow us to calculate a minimum gestation length of 0.54 years for M. edwardsi, compared to 0.70 years in Gorilla. Postnatal crown and root formation in M. edwardsi 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 Megaladapis 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. [ABSTRACT FROM AUTHOR]

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 (Proconsul and Sivapithecus). 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 Homo and anatomically modern Homo sapiens 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 Homo erectus s.l. and Middle Pleistocene specimens and the later Neandertal groups. Furthermore, the dental models of anatomically modern Homo sapiens 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 i) to interpolate missing data or ii) place individuals in predetermined groups. [ABSTRACT FROM AUTHOR]

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 Homo heidelbergensis species, whereas the TD6 hominins are representative of Homo antecessor, 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. [ABSTRACT FROM AUTHOR]

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 A. africanus (from Sterkfontein), A. robustus (Swartkrans, Drimolen and Sterkfontein) and South African early Homo (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 A. africanus and A. robustus 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 A. africanus and A. robustus; b) significant differences between the two species in relative cusp areas are evident for the protocone of M1 (with A. africanus larger than A. robustus), the paracone of M1, and the protocone of M2 and M3 (with A. robustus larger than A. africanus); c) in the total crown area A. robustus shows the sequence M1M3, as in living apes. This different sequence between A. africanus and A. robustus appears to be related mostly to differences in mesial cusp size, which in A. robustus shows a marked relative expansion from M1 to M3. Also, the variability in absolute cusp areas of the A. africanus sample seems to be related to the presence of specimens with notably large teeth. [ABSTRACT FROM AUTHOR]

We have examined the crowns of chimpanzee, australopith, and Paranthropus species and early Homo 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 Homo, and an increase in crown size and morphological complexity in Paranthropus. A phenetic assessment of maxillary and mandibular molar crown non-metrical traits revealed that two australopith species (Au. africanus and Au. afarensis) are much more similar to each other than either is to Paranthropus, and together all hominins are distinctively different from chimpanzees (P. troglodytes and P. paniscus). The difference between Paranthropus 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 Paranthropus 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 4 talonid. Early Homo 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 Pan, and similar to the australopiths, early Homo possesses a larger P4 with a somewhat expanded talonid, but this trend is subsequently reversed in later Homo. Our study reveals that some of the dental trends said to be characteristic of Homo actually appear relatively late in human evolution. [ABSTRACT FROM AUTHOR]

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 Homo and Pan and following these, Gorilla and Pongo. Except for Pan, however, modern hominids lack taxonomic diversity, since by most accounts each one is represented by a single living species. Pan is the sister taxon to modern humans and it is represented by two living species. As such the species of Pan have greater relevance for studying interspecific variation in fossil hominin taxonomy. Despite their relatively impoverished species representations Pan troglodytes, Gorilla gorilla and Pongo pygmaeus 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 P. pygmaeus, G. gorilla, P. troglodytes and P. paniscus. 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 P. t. troglodytes (n = 152), P. t. verus (n = 64), P. t. schweinfurthii (n = 79), G. g. gorilla (n = 208), G. g. graueri (n = 61), G. g. beringei (n = 30), P. p. pygmaeus (n = 140), and P. p. abelii (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 Pan 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. Pan troglodytes troglodytes and P. troglodytes schweinfurthii were separated by the least dental distance. P. troglodytes verus was separated by a greater distance from these two, but on the whole the distances among subspecies of P. troglodytes were less than among subspecies of G. gorilla and P. pygmaeus. The dental distance between G. g. gorilla and G. g. graueri was greater than that observed between P. troglodytes and P. paniscus. With size adjustment intergroup distances between gorilla subspecies were reduced, resulting in distances comparable to subspecies of P. troglodytes. 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. [ABSTRACT FROM AUTHOR]