Rethinking incisor size and diet in anthropoids: diet, incisor wear and incisor breadth in the African apes

In a seminal study Hylander (1975) concluded that the length of the incisor row in catarrhines considered frugivores is longer relative to body mass than in those classified as folivores. Assuming that large fruits require greater incisal processing than do leaves, stems, berries, and seeds, he argued that the larger incisors of frugivores increased their resistance to wear. The present analysis examines diet, incisor wear, and incisor crown breadth in cranial samples of western lowland gorillas and chimpanzees. Incisor wear rate was assessed on the basis of the extent of incisor crown reduction observed at sequential stages of first molar wear. Incisor metrics were obtained from the unworn teeth of juveniles. Results suggest that incisor wear is greater in the more folivorous western lowland gorillas than in more frugivorous chimpanzees. Moreover, incisor crown dimensions do not differ appreciably among African apes. These findings fail to support the hypothesis that slower wear rates are associated with broader incisor crowns, and raise new questions regarding the significance of incisor row length in anthropoids.     

Dental topography and molar wear in Alouatta palliata from Costa Rica

Paleoprimatologists depend on relationships between form and function of teeth to reconstruct the diets of fossil species. Most of this work has been limited to studies of unworn teeth. A new approach, dental topographic analysis, allows the characterization and comparison of worn primate teeth. Variably worn museum specimens have been used to construct species-specific wear sequences so that measurements can be compared by wear stage among taxa with known differences in diet. This assumes that individuals in a species tend to wear their molar teeth in similar ways, a supposition that has yet to be tested. Here we evaluate this assumption with a longitudinal study of changes in tooth form over time in primates. Fourteen individual mantled howling monkeys (Alouatta palliata) were captured and then recaptured after 2, 4, and 7 years when possible at Hacienda La Pacifica in Costa Rica between 1989-1999. Dental impressions were taken each time, and molar casts were produced and analyzed using dental topographic analysis. Results showed consistent decreases in crown slope and occlusal relief. In contrast, crown angularity, a measure of surface jaggedness, remained fairly constant except with extreme wear. There were no evident differences between specimens collected in different microhabitats. These results suggest that different individual mantled howling monkeys wear their teeth down in similar ways, evidently following a species-specific wear sequence. Dental topographic analysis may therefore be used to compare morphology among similarly worn individuals from different species.     

Patterns of molar wear in hunger-gatherers and agriculturalists

Tooth wear records valuable information on diet and methods of food preparation in prehistoric populations or extinct species. In this study, samples of modern and prehistoric hunger-gatherers and agriculturalists are used to test the hypothesis that there are systematic differences in patterns of tooth wear related to major differences in subsistence and food preparation. Flatness of molar wear is compared for five groups in hunger-gatherers (N = 298) and five groups of early agriculturalists (N = 365). Hunger-gatherers are predicted to develop flatter molar wear due to the mastication of tough and fibrous foods, whereas agriculturalists should develop oblique molar wear due to an increase in the proportion of ground and prepared food in the diet. A method is presented for the quantitative measurement and analysis of flatness of molar wear. Comparisons of wear plane angle are made between teeth matched for the same stage of occlusal surface wear, thus standardizing all groups to the same rate of wear. Agriculturalists develop highly angled occlusal wear planes on the entire molar dentition. Their wear plane angles tend to exceed hunger-gatherers by about 10 degrees in advanced wear. Wear plane angles are similar within subsistence divisions despite regional differences in particular foods. This approach can be used to provide supporting evidence of change in human subsistence and to test dietary hypotheses in hominoid evolution.     

The relation of canine size to pattern and extent of attrition in baboons

For most genera of animals the association between dental morphology and diet is such that inferences concerning the diet can be made on the basis of the dentition alone. The canine is the one tooth that appears exempt from such generalisation and exhibits a wide range of variability of size and shape in all groups. In order to determine the effect of dimorphism of the canine on the dental apparatus, male and female specimens of Theropithecus and Papio baboons were examined. Occlusal relationships and dental pathology for 21 Theropithecus and 40 Papio skulls were recorded, and crown height measurements obtained for maxillary incisors, buccal and lingual molar cusps. Attrition was the most common and severe cause of abscess formation in older animals: the pattern of attrition differed in adult males and females, the latter showing more wear of the incisor and lingual molar cusps. Partial correlations for incisor, buccal and lingual molar cuspal crown height show a significant correlation between incisor and lingual cusp attrition in juveniles of both sexes and adult females (p < 0.01). Adult males show no correlation of attrition. It is proposed that the correlation of incisor and lingual molar cusp attrition is associated with anterior-posterior grinding movements, such as take place during incision, that the large canine present in the male limits such movements, the sharp blade-like canine being employed as a cutting tool. This use of the canine by reducing functional demands on other teeth, prolongs the utility of the dental apparatus, and hence the lifespan of its possessor.     

Relationships between the diet and dentition of Asian leaf monkeys

Colobines have been generally described as primates that use the anterior teeth minimally, but the posterior teeth extensively, to process leaves and related food items. However, variation among leaf monkeys in both anterior and posterior dental morphology has been recognized for decades. In this study, we turn to Hylander's (Science 189 (1975) 1095-1098) analysis of anterior incisor row length and Kay's (Adaptations for foraging in nonhuman primates, 1984) examination of relative molar crest length to test hypotheses proposed by them for Asian colobines. We present findings based on data from the largest Asian colobine sample measured to date. Our findings for incisor row length and molar cresting are not amenable to broad generalizations. In those instances when our morphological findings concur with those of Hylander (Science 189 (1975) 1095-1098) and Kay and Hylander (The ecology of arboreal folivores, 1978), the ecological evidence seldom supports the morphological predictions. The disassociation between diet and dental patterns may be a consequence of differential selection by fallback foods, anthropogenic disturbance or climatic shifts limiting preferred diets, or the use of food types as opposed to food mechanical properties for dietary categorization. We also found that in the case of both incisor row length and molar crest length, the patterns for males and females differed markedly. The reasons for these differences may in part be ascribed to the metabolic challenges faced by females and subsequent niche partitioning. We propose integrated analyses of the ingestive and digestive systems of our study taxa to clarify relationships among behavior, dental morphology, and diet in extant and extinct colobines.     

The ecology and evolution of tooth wear in red deer and moose

Differences in body size and diet type (browser–grazer continuum) have formed functional traits of ruminants, including tooth design. Grazers and mixed-feeders eat a more fibrous diet than browsers, which arguably increase tooth wear. Tooth wear has also been suggested to increase with body size. Moreover, for species with large distribution ranges, different populations may be exposed to very different ecological factors affecting diet and thus tooth wear rates. Therefore, evolutionary history and contemporary ecological conditions, both operating through diet, may be important for patterns of tooth wear. Here, we compare inter- and intraspecific rates of tooth wear in multiple populations of one large browser (moose Alces alces ) and one mixed-feeder (red deer Cervus elaphus ) covering the main distribution range of each species in Norway. We found that the mixed-feeding red deer wore teeth faster than the larger and browsing moose, suggesting that feeding-type was more important than body size for patterns of wear. There was substantial spatial variation in tooth wear rates, but the inter-specific difference in wear was consistent. Molar wear rates, but not incisors wear rates, in the browser were less variable between populations than in the mixed-feeder. There was no close link between incisor and molar wear rates at the population level. Our findings are consistent with the view that both evolution related to diet type and current ecological conditions (being proxies for within-species variation in diet quality) are important for patterns of tooth wear.     

Tooth wear patterns in voles (Microtus agrestis and Clethrionomys glareolus) and efficiency of dentition in preparing food for digestion

Voles (Microtinae) are among the smallest of mammals which feed extensively on plant leaf material. They achieve higher digestive efficiencies than large ungulates, and this study considers the role that dentition may play in grinding food into small particles, so assisting efficient digestion. Bank ( Clethrionomys glareolus) and field voles ( Microtus agrestis) were found to chew their food into far smaller particles than ungulates, field voles producing smaller particle sizes than bank voles. Scanning electron micrographs showed differences in tooth wear patterns between species, and in bank voles a change in diet led to changes in tooth wear and to changes in the efficiency with which food was processed. Field voles have a pore structure on the occlusal surface of the molar teeth which could play an important role because when the teeth act antagonistically these pores could grate fragments of plant leaves into very small particles and hence enable the animals to achieve high digestive efficiencies.     

Tooth wear and dental pathology of the Bronze-Iron Age people in Xinjiang, Northwest China: Implications for their diet and lifestyle

Tooth wear and dental pathology related to diet and lifestyle were investigated in the human dental remains unearthed from three archaeological sites of Bronze Age and Iron Age in Xinjiang of northwest China, and in comparative samples from two Neolithic sites in Henan and Shanxi in central China along the Yellow River.Our results indicate that the average tooth wear on most tooth types in the three Xinjiang sites was close to those of the Neolithic samples from central China. The variation within the Xinjiang samples was also explored. Some special wear patterns such as severe wear on the first molar and relatively heavy wear of anterior teeth were observed on the specimens from the Xinjiang sites. Obvious differences in caries and antemortem tooth loss were found between Xinjiang and comparative samples with higher frequencies of caries observed in samples from central China and higher antemortem tooth loss in samples from the Xinjiang sites. Strongly developed exostoses (tori) were also identified on mandibles and maxillae of the specimens from Xinjiang.The authors believe that the differences in tooth wear and dental pathology between Xinjiang and central China were caused by differences in diet and lifestyle. Food of a harder texture was consumed by the people who lived in Xinjiang than by the people in Henan and Shanxi of central China. The higher occurrence of heavily worn anterior teeth and some other special wear patterns, antemortem tooth loss and presence of exostoses on jaw bones in Xinjiang suggest that the people in Xinjiang lived in a relatively harsh environment, frequently gnawing hard objects, or using teeth as some kind of tools. All these activities put masticatory organs under a heavy load. The differences in caries frequencies between the frontier and central areas of China indicate that food richer in carbohydrates was consumed by the people in the central areas.It is proposed that about 3000-2000 years BP in many areas of frontier Xinjiang, people mainly relied on the type of hunter-gatherer economy with agriculture playing a smaller role in their lifestyle.     

Tooth morphology and other aspects of the Teso dentition

The teeth of over 5,000 Teso schoolchildren members of a Nilo-Hamitic tribe in East Africa, were examined for morphological traits. There was a significant difference between the sexes in the number of cusps on the lower first and second molars, in the prevalence of the cusp of Carabelli, and in variability and agenesis of the upper lateral incisor. The results showed that females consistently favoured tooth reduction. There was also a tendency among those possessing extra cusps on one molar to have extra cusps or other molars. Records kept of the prevalence of the tribal custom of extracting lower central incisors indicated that this practise is rapidly dying out. On another group of teeth which had been extracted from adults common variations of root morphology were noted, together with the fissure pattern of the lower molars. Measurements were made of those teeth which were unworn and were not broken down by dental decay, and the lower third molar was found to be the largest tooth of the series. Observations on the pattern of molar tooth wear showed that the buccal as well as the occlusal surface was strongly affected.     

Exploring the relationship between dental wear and status in late medieval subadults from England

Dental wear patterns were recorded on 458 deciduous molar teeth, of 142 subadults from late medieval (AD 1086–1539) England, to explore the relationship between dental wear and burial status of children. A new ordinal method for scoring dental wear stages on the deciduous molar teeth was devised. It was postulated that if a discernible relationship between dental wear stage and burial location could be seen then this could reflect a difference in diet between those receiving higher or lower status burial. The dental wear stages recorded were statistically similar for the dentitions of subadults from different cemeteries, as well as from different burial locations, indicating a comparable diet for the children studied. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.     

Changes in articular eminence morphology with dental function

Measurements of mandibular fossa depth and slope of the articular eminence were obtained for human skeletal samples chosen to represent a wide spectrum of subsistence strategies and oral function: hunter-gatherers (Eskimos, Australians), American Indians dependent to a variable extent on maize agriculture, and early twentieth century American whites and blacks. In the Eskimo and Australian samples, a generalized and steady increase in fossa depth and slope was observed with increasing functional age (tooth wear) through wear level 5 (of 8), followed by a levelling off or slight decrease in fossa depth in later wear levels on the anterior teeth and a sharp decrease in fossa depth in later wear levels on the molars. Although much less consistent due in part to extensive and early molar loss, patterns of variation in the remaining samples were characterized overall by a decrease in fossa depth and slope with increasing wear, especially on the molars. Further, in those samples with high incidences of posterior tooth loss, fossa depth was routinely less and the eminence more gently sloped in subsamples having experienced molar loss than in subsamples retaining all their molars. These data provide evidence that the temporomandibular joint (TMJ) undergoes continuous morphological alteration throughout adult life, and that these alterations are probably mediated by dental function. Moreover, they suggest that differences in patterning of such alterations may exist among human groups with contrasting patterns of tooth use.     

Tooth wear in eastern grey kangaroos (Macropus giganteus) and western grey kangaroos (Macropus fuliginosus), and its potential influence on diet selection, digestion and population parameters

As teeth wear in eastern and western grey kangaroos, the pattern of enamel ridges changes. This affects the amount of available cutting edges and consequently the masticatory efficiency. These kangaroos also have molar progression. There is evidence for the independence of rates of tooth wear and molar progression, and variation is found in the maximum amount of wear attained by teeth both within and between populations. This variation has the potential to affect diet selection, digestion and population parameters.     

Occlusal relief changes with molar wear in Pan troglodytes troglodytes and Gorilla gorilla gorilla

Most research on primate tooth form-function relationships has focused on unworn teeth. This study presents a morphological comparison of variably worn lower second molars (M(2)s) of lowland gorillas (Gorilla gorilla gorilla; n=47) and common chimpanzees (Pan troglodytes troglodytes; n=54) using dental topographic analysis. High-resolution replicas of occlusal surfaces were prepared and scanned in 3D by laser scanning. The resulting elevation data were used to create a geographic information system (GIS) for each tooth. Occlusal relief, defined as the ratio of 3D surface area to 2D planometric area of the occlusal table, was calculated and compared between wear stages, taxa, and sexes. The results failed to show a difference in occlusal relief between males and females of a given taxon, but did evince differences between wear stages and between taxa. A lack of significant interaction between wear stage and taxon factors suggests that differences in occlusal relief between chimpanzees and gorillas are maintained throughout the wear sequence. These results add to a growing body of information on how molar teeth change with wear, and how differences between primate species are maintained at comparable points throughout the wear sequence. Such studies provide new insights into form-function relationships, which will allow us to infer certain aspects of diet in fossils with worn teeth.     

Wear Fast,Die Young: More Worn Teeth and Shorter Lives in Iberian Compared to Scottish Red Deer

Teeth in Cervidae are permanent structures that are not replaceable or repairable; consequently their rate of wear, due to the grinding effect of food and dental attrition, affects their duration and can determine an animal''s lifespan. Tooth wear is also a useful indicator of accumulative life energy investment in intake and mastication and their interactions with diet. Little is known regarding how natural and sexual selection operate on dental structures within a species in contrasting environments and how these relate to life history traits to explain differences in population rates of tooth wear and longevity. We hypothesised that populations under harsh environmental conditions should be selected for more hypsodont teeth while sexual selection may maintain similar sex differences within different populations. We investigated the patterns of tooth wear in males and females of Iberian red deer (Cervus elaphus hispanicus) in Southern Spain and Scottish red deer (C. e. scoticus) across Scotland, that occur in very different environments, using 10343 samples from legal hunting activities. We found higher rates of both incisor and molar wear in the Spanish compared to Scottish populations. However, Scottish red deer had larger incisors at emergence than Iberian red deer, whilst molars emerged at a similar size in both populations and sexes. Iberian and Scottish males had earlier tooth depletion than females, in support of a similar sexual selection process in both populations. However, whilst average lifespan for Iberian males was 4 years shorter than that for Iberian females and Scottish males, Scottish males only showed a reduction of 1 year in average lifespan with respect to Scottish females. More worn molars were associated with larger mandibles in both populations, suggesting that higher intake and/or greater investment in food comminution may have favoured increased body growth, before later loss of tooth efficiency due to severe wear. These results illustrate how independent selection in both subspecies, that diverged 11,700 years BP, has resulted in the evolution of different longevity, although sexual selection has maintained a similar pattern of relative sex differences in tooth depletion. This study opens interesting questions on optimal allocation in life history trade-offs and the independent evolution of allopatric populations.     

Taxonomic attribution of the La Grive hominoid teeth

The two hominoid teeth—a central upper incisor (NMB G.a.9.) and an upper molar (FSL 213981)—from the Middle Miocene site of La Grive‐Saint‐Alban (France) have been traditionally attributed to Dryopithecus fontani (Hominidae: Dryopithecinae). However, during the last decade discoveries in the Vallès‐Penedès Basin (Spain) have shown that several hominoid genera were present in Western Europe during the late Middle Miocene. As a result, the attribution of the dryopithecine teeth from La Grive is not as straightforward as previously thought. In fact, similarities with the upper incisor of Pierolapithecus have led to suggestions that either the latter taxon is present at La Grive, or that it is a junior synonym of Dryopithecus. Here, we re‐describe the La Grive teeth and critically revise their taxonomic assignment based on metrical and morphological comparisons with other Middle to Late Miocene hominoids from Europe and Turkey, with particular emphasis on those from the Vallès‐Penedès Basin. Our results suggest that the I¹ differs in several respects from those of Pierolapithecus and Hispanopithecus, so that an attribution to either Dryopithecus or Anoiapithecus (for which this tooth is unknown) seems more likely. The molar, in turn, most likely corresponds to the M¹ of a female individual. Compared to other Middle Miocene taxa, its occlusal morphology enables its distinction from Pierolapithecus, whereas relative crown height agrees well with Dryopithecus. Therefore, based on available evidence, we support the traditional attribution of the La Grive hominoid to D. fontani. Am J Phys Anthropol 151:558–565, 2013. © 2013 Wiley Periodicals, Inc.     

Dental wear among cercopithecid monkeys of the Taï forest,Côte d'Ivoire

Studies of dental macrowear can be useful for understanding masticatory and ingestive behavior, life history, and for inferring dietary information from the skeletal material of extinct and extant primates. Such studies to date have tended to focus on one or two teeth, potentially missing information that can be garnered through examination of wear patterns across the tooth row. Our study measured macrowear in the postcanine teeth of three sympatric cercopithecid species from the Taï Forest, Côte d'Ivoire (Cercocebus atys, Procolobus badius, and Colobus polykomos), whose diets have been well‐described. Inter‐specific analyses suggest that different diets and ingestive behaviors are characterized by different patterns of wear across the molar row, with Cercocebus atys emphasizing tooth use near P₄‐M₁, P. badius emphasizing a large amount of tooth use near M₂‐M₃, and Colobus polykomos exhibiting wear more evenly across the postcanine teeth. Information regarding differential tooth use across the molar row may be more informative than macrowear analysis of isolated teeth for making inferences about primate feeding behavior. Am J Phys Anthropol 150:655–665, 2013. © 2013 Wiley Periodicals, Inc.     

Distribution of enamel on the incisors of Old World monkeys

Longitudinal ground sections of 29 Old World monkey central lower incisors were studied histologically and metrically. Labiolingual incisor width tended to scale isometrically with body weight but with important deviations in relative incisor size, which appeared to be correlated with diet in accord with work by Hylander. Lower incisors of the predominantly folivorous colobine monkeys had a substantial layer of enamel on both lingual and labial aspects and consequently had blunt incisal edges. These teeth in both cercopithecins and papionins, which are omnivorous or frugivorous, had little or no enamel on the lingual aspect, resulting in sharp incisal edges. It is suggested that colobine incisors are used mainly in gripping and tearing leaves, whereas cercopithecine incisors are better adapted to cutting and scraping. Crown height showed a positive allometric relationship with overall incisor height, so that the tall incisors of papionins, especially Papio and Mandrillus, were more hypsodont than the shorter incisors of colobines and cercopithecins. This appears to be related to differences in the rates of incisor wear between the groups.     

Dental microwear in live, wild-trapped Alouatta palliata from Costa Rica

One problem with dental microwear analyses of museum material is that investigators can never be sure of the diets of the animals in question. An obvious solution to this problem is to work with live animals. Recent work with laboratory primates has shown that high resolution dental impressions can be obtained from live animals. The purpose of this study was to use similar methods to begin to document rates and patterns of dental microwear for primates in the wild. Thirty-three Alouatta palliata were captured during the wet season at Hacienda La Pacifica near Canas, Costa Rica. Dental impressions were taken and epoxy casts of the teeth were prepared using the methods of Teaford and Oyen (1989a). Scanning electron micrographs were taken of the left mandibular second molars at magnifications of 200x and 500x. Lower magnification images were used to calculate rates of wear, and higher magnification images were used to measure the size and shape of microwear features. Results indicate that, while basic patterns of dental microwear are similar in museum samples and samples of live, wild-trapped animals of the same species, ecological differences between collection locales may lead to significant intraspecific differences in dental microwear. More importantly, rates of microwear provide the first direct evidence of differences in molar use between monkeys and humans.     

Wear striations on the incisors of ceropithecid monkeys as an index of diet and habitat preference

Wear striations on the incisors of Old World monkeys were examined in order to determine associations between the distributions of striations, diet, and habitat preference. Significant differences exist between the Cercopithe-cinae and the Colobinae in respect to the orientation of incisor wear striations. In the Colobinae striations are oriented in a predominantly mesiodistal direction. In the Cercopithecinae striations usually have a labiolingual orientation. Comparisons of terrestrial and arboreal genera indicate that significant differences exist between the two groups in respect to the density of striations on the oc-clusal wear facets of maxillary central incisors. Arboreal and terrestrial monkeys also differ in the frequency of individual incisor wear facets completely devoid of wear striations.