Playing 'possum: A microwear experiment

A recent experiment to evaluate the reliability of dental microwear as an indicator of diet seems to show that differences in diets fed to laboratory animals are not reflected by their tooth wear. We feel that these results are misleading, and reflect not so much the limits of microwear analysis per se, but rather result from the problems of design and execution inherent in any experimental simulation of natural feeding behavior. The experiment in question was flawed in several respects, and we think that changes in the methods and assumptions of the study are necessary before the experimental approach can yield meaningful results with which to test hypotheses about microwear analyses.     

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.     

Dust accumulation in the canopy: A potential cause of dental microwear in primates

Dental microwear researchers consider exogenous grit or dust to be an important cause of microscopic wear on primate teeth. No study to date has examined the accumulation of such abrasives on foods eaten by primates in the forest. This investigation introduces a method to collect dust at various heights in the canopy. Results from dust collection studies conducted at the primate research stations at Ketambe in Indonesia, and Hacienda La Pacifica in Costa Rica indicate that 1) grit collects throughout the canopy in both open country and tropical rain forest environments; and 2) the sizes and concentrations of dust particles accumulated over a fixed period of time differ depending on site location and season of investigation. These results may hold important implications for the interpretation of microwear on primate teeth. © 1995 Wiley-Liss, Inc.     

Dental microwear features as an indicator for plant food in early hominids: A preliminary study of enamel

Studies of dental microwear have shown qualitative and quantitative differences related with specific diets of mammals. Here we report a classification of the features of microwear and the results of a comparative study of the characteristics of wear produced by plant food. Species which are mainly folivorous or herbivorous show common features useful for providing information about the diet of early hominids at Garusi and Laetoli (Tanzania), Hadar (Ethiopia) and Olduvai (Tanzania).     

Enamel structure and microwear: an experimental study of the response of enamel to shearing force.

The anisotropic fracturing and differential wear properties of enamel microstructure represent factors that can obscure the predictive relationship between dental microwear and diet. To assess the impact of enamel structure on microwear, this in vitro experimental study examines the relative contributions to wear of three factors: 1) species differences in microstructure, 2) direction of shearing force relative to enamel prisms and crystallites, and 3) size of abrasive particles. Teeth of Lemur, Ovis, Homo, and Crocodylus, representing, respectively, the structural categories of prismatic patterns 1, 2, and 3 and nonprismatic enamel, were abraded by shearing forces (forces having a component directed parallel to abraded surfaces) and examined by scanning electron microscopy. Striation width increased with particle size for nonprismatic, but not for prismatic, specimens. Direction of shear relative to prism and crystallite orientation had a significant influence on striation width in only some prismatic enamels. The different responses of prismatic and nonprismatic enamels to abrasion reflect the influence of structure, but at the level of organization of crystallites rather than prisms per se. Such interactions explain in part the inability of striation width to discriminate among animals with different dietary habits. Heteroscedasticity and deviations from normality also may confound parametric analyses of microwear variables. Variation in crystallite orientation in prismatic enamels may contribute to optimal dental function through the property of differential wear in functionally distinct regions of teeth.     

Molar microwear in extant small-bodied faunivorous mammals: An analysis of feature density and pit frequency

This study quantitatively examined molar microwear in nine species of extant small-bodied faunivorous primates and microchiropterans. Comparative analyses were performed within the food category faunivory, both between hard- and soft-object feeding faunivores and between primarily insectivorous and carnivorous taxa. Additionally, microwear in faunivores was compared to that reported in the literature for frugivorous and folivorous primates. The results indicated that although insectivores and carnivores could not be distinguished by microwear analyses, hard-object faunivores (i. e., those that primarily consume beetles or actively comminute bone) can be readily distinguished from soft-object faunivores (i. e., moth, caterpillar, or vertebrate flesh specialists). The hard-object faunivores consistently exhibited greater pit frequencies (in excess of 40%). Furthermore, comparisons of these microwear data on faunivorous mammals to previous work on frugivorous and folivorous primates (Teaford, 1988, pers. comm.; Teaford and Runestad, 1992, pers. comm.; Teaford and Walker: American Journal of Physical Anthropology 64:191–200, 1984) permitted three observations to be made. 1) Faunivores tend to have higher mean feature densities than either frugivores or folivores, although these differences are not consistently statistically distinct. 2) Faunifores and frugivores that feed on hard-objects have comparable mean pit frequencies. 3) Although it is impossible to distinguish faunivores and folivores on the basis of metric analysis of gross molar morphology, this distinction can be made on microwear criteria. Both hard- and soft-object faunivores exhibit much higher mean pit frequencies than primarily folivorous species. © 1993 Wiley-Liss, Inc.     

Seasonal or ecological differences in diet and molar microwear in Cebus nigrivittatus

Dental microwear analyses have raised new hopes and questions for functional morphologists. One hope is that analyses will allow insights into subtle dietary differences of extinct species. One major question is whether seasonal and/or habitat differences in dental microwear are reliably detectable. The extensive collections of Cebus nigrivittatus obtained by the Smithsonian Venezuelan Project allowed us to examine seasonal and habitat differences in dental microwear. Specimens were collected from three distinct ecological life zones that are distinguished by both the amount of rainfall and its seasonability. Environmental variation is generally correlated with variation in resource availability which, in C. nigrivittatus, affects diet. Published field studies indicate that these animals depend more on dry hard fruit and chitinous invertebrates during drier times and succulent fruits and caterpillars during wetter times of the year. As in previous microwear analyses, epoxy replicas were prepared from dental impressions, and the replicas were examined under a scanning electron microscope. Two micrographs were taken of facet 9 on M² of each specimen. Mean values for the proportion of pits (vs. scratches), pit wdith, and scratch width were computed for each of 62 individuals and compared between ecological zones and collecting dates by using a multiple comparison test. Results indicate that, while seasonal differences in molar microwear in C. nigrivittatus are perhaps reliably detectable, 1) they are small in magnitude, 2) they are only detectable in certain ecological life zones, and 3) they are not of the order of magnitude that will obscure major interspecific differences in molar microwear such as those between C. apella and C. nigrivittatus.     

Live primates and dental replication: new problems and new techniques

Dental microwear analyses are beginning to provide new insights into the intricacies of jaw movement and tooth use in modern and extinct mammals. However, these analyses are also raising new questions that are best answered through studies of live animals with known diets. The process of taking dental impressions from live animals is a difficult one that presents problems different from those encountered in working with museum material. This report presents a review of some of those problems together with solutions that have been developed in the course of laboratory work with nonhuman primates. It also summarizes recent developments in dental casting.     

Dental microwear and mechanisms in early hominids from Laetoli and Hadar

The dentition of early hominids from Laetoli and Hadar provide evidence of "incisal stripping" and a shear-grinding action for C/P3 complex through microscopic examination of wear facets on dental crowns. This masticatory pattern of dental wear resembles that of Papio papio and suggests behavioral analogies between early hominids and Papio.     

Terrestrial foraging and dental microwear inPapio ursinus

Dental microwear of ten wild-shot chacma baboons (Papio urinus) form Northwest and Northern Privinces, South Africa was examined by scanning electron microscopy. All specimens were collected during the dry season, during which these primates exploit hypogeous (underground) food items, including tubers and corms. The microwear fabric of thisP. ursinus sample is characterized by high pitting frequencies and large microwear features. It differs significantly from those displayed by other terrestrially foraging papionins of the genusTheropithecus. Exogenous grit is hypothesized to be largely responsible for the observedP. ursinus wear pattern, which resembles the microwear profiles of durophagous primates. It is suggested that large microwear features and a high incidence of enamel pitting, which are generally held to represent a microwear “signature” of durophagy, may not always be indicative of hard-object feeding in anthropoid primates.     

Buccal dental microwear variability in extant African Hominoidea: taxonomy versus ecology

Buccal microwear patterns on teeth are good indicators of the abrasiveness of foodstuffs and have been used to trace the dietary habits of fossil species, including primates and hominids. However, few studies have addressed the variability of this microwear. The abrasiveness of dietary components depends not only on the hardness of the particles ingested, but also on the presence of dust and other exogenous elements introduced during food processing. These elements are responsible for the microwear typology observed on the enamel surfaces of primate teeth. Here we analyzed the variability of buccal microwear patterns in African Great Apes (Gorilla gorilla and Pan troglodytes), using tooth molds obtained from the original specimens held in several osteological collections. Our results suggest that ecological adaptations at subspecies or population level account for differences in microwear patterns, which are attributed to habitat and ecological conditions within populations rather than differences between species. The findings from studies on the variability of buccal dental microwear in extant species will contribute to a better understanding of extinct hominids’ diet and ecology.     

Preliminary examination of non-occlusal dental microwear in anthropoids: Implications for the study of fossil primates

Most studies of microscopic wear on non-human primate teeth have focused on the occlusal surfaces of molars. Recent analyses of the buccal surfaces of human cheek teeth have demonstrated an association between diet and dental microwear on the these surfaces as well. In the current study, we examine microwear on both the buccal and lingual surfaces of non-human primate molars to assess the potential of these surfaces to reveal information concerning anthropoid feeding behaviors. We compare frequency of microwear occurrence in 12 extant and 11 fossil anthropoid species. Among the living primates, the occurrence of microwear on non-occlusal surfaces appears to relate to both diet and degree of terrestriality. The implications of this research for the inference of feeding behaviors and substrate use in fossil cercopithecoids are discussed. © 1996 Wiley-Liss, Inc.     

More lingual surface attrition of the maxillary anterior teeth in American Indians: prehistoric Panamanians

Lingual surface attrition of the maxillary anterior teeth (LSA-MAT) has been found in additional prehistoric Latin American Indian skeletons. LSAMAT was first observed in crania from an Archaic Brazilian site. This second finding occurs in teeth from Venado Beach, a late prehistoric site in Panama. LSAMAT is also present in some fragmentary specimens from the Archaic Cerro Mangote site in Panama. LSAMAT at Venado Beach is present in 57% of 28 adult crania. As in the Brazilian study, LSAMAT is associated with a high caries rate (82% of 50 adults; 11.7% of 852 permanent teeth). As first suggested, eating and processing of some type of abrasive carbohydrate food, such as manioc, is the possible cause of LSAMAT. However, other possible causes relating to habitation on or near marine coasts cannot be totally ruled out.     

Hanuman Langur: Monkey of India

An apparently new type of dental wear pattern, lingual surface attrition of the maxillary anterior teeth (LSAMAT), has been found in 85% of 46 adult crania from a 3000–4200 BP Archaic site called Corondó near the Atlantic Ocean coast of Brazil. LSAMAT is associated with a high caries rate (60% of 77 adults; 11% of 1,219 permanent teeth) in what on archeologica grounds alone would be considered a mainly meat-eating population. It is suggested that both LSAMAT and caries resulted from eating some starchy plant like manioc.     

Development of the helicoidal plane

In this study of thebelicoidal occlusal plane the relationships between tooth wear, the transverse slopes of mandibular molars and dental arch breadths were examined in 74 pre-contemporary Australian Aboriginal skulls. With increasing age and tooth wear the orientation of the mandibular occlusal surfaces increased towards the buccal. The differential occlusal orientation from first to third molars, present at eruption, tended to increase progressively with tooth wear. These functionally induced changes, together with regional differences in relative breadths of the maxillary and mandibular dental arches, are important in the development of abelicoidal occlusal plane.     

Quantitative analysis of dental microwear in threespine stickleback: a new approach to analysis of trophic ecology in aquatic vertebrates

1. The threespine stickleback Gasterosteus aculeatus is an important model organism in studies of genomic and phenotypic evolution, adaptation and speciation. Fossil Gasterosteus offer the potential to test models derived from studies of extant fishes over true evolutionary time-scales. Competition for food resources, for example, plays an important part in stickleback speciation, causing divergence in food gathering traits and ecological character displacement, but it is not possible to test this model in fossils because evidence of diet is almost never preserved. 2. We demonstrate here that quantitative analysis of dental microwear, a technique previously applied only to mammals, provides a reliable guide to the dietary preferences of stickleback. Teeth from stickleback raised under laboratory conditions exhibit microwear patterns that vary systematically according to substrate coarseness and whether fishes feed on Daphnia within the water column, or on chironomid larvae from the bottom. Furthermore, microwear data exhibit a progressive shift in their distribution that tracks differences in experimental feeding treatments. 3. Microwear in wild populations also exhibits a relationship with feeding. In blind assessments of trophic niche based on microwear patterns we were able to correctly assign all but one equivocal population to trophic group. Microwear data from wild stickleback exhibit a shift in distribution comparable with that observed across the range of treatments in the laboratory and these allow populations to be ranked according to the degree to which they approach fully benthic or fully limnetic feeding. 4. Our results demonstrate that microwear has the potential to be a powerful tool in the analysis of fish trophic ecology, particularly in the analysis of species pairs and niche differentiation. It has advantages over the trophic snapshot provided by analysis of stomach contents in that microwear reflects feeding and food preferences over a longer period of time, and can be applied where these data are unavailable. Furthermore, it is applicable to extinct organisms and fossils, allowing the role of trophic ecology, niche partitioning and competition over evolutionary time-scales to be investigated for the first time.