Testing Dietary Hypotheses of East African Hominines Using Buccal Dental Microwear Data

Lifestyle changes and its effect towards the evolution of human dentition

Background

The dentition of modern humans has evolved from their hominid ancestors to their current form. Factors regarding the changes of lifestyle such as dietary habits and usage of tools have affected the evolution of human dentition. This article aimed to discuss the effect of dietary changes on the evolution of human teeth. An online literature search in the PubMed database was conducted according to the inclusion criteria of this study.

Main body

The culture transition from a hunter-gatherer society to agriculture is followed by dietary changes, which result in a decrease of tooth wear due to more refined food sources in agricultural intensification. By analyzing the microwear pattern such as shear, striation, and pattern of the buccal teeth, the dietary hypothesis based on the occlusal tooth microwear analysis could be examined.

Conclusion

The dietary hypothesis based on the occlusal tooth microwear study could be tested by analyzing the microwear pattern (shear, striation, pattern) of the buccal teeth. Posterior teeth are more closely related to diet, while anterior teeth are related to non-dietary tooth-use behaviors, or using the teeth as a tool or third hand which causes more limited striations at the labial surface.

Clarifying relationships between cranial form and function in tapirs, with implications for the dietary ecology of early hominins

Paleontologists and paleoanthropologists have long debated relationships between cranial morphology and diet in a broad diversity of organisms. While the presence of larger temporalis muscle attachment area (via the presence of sagittal crests) in carnivorans is correlated with durophagy (i.e. hard-object feeding), many primates with similar morphologies consume an array of tough and hard foods—complicating dietary inferences of early hominins. We posit that tapirs, large herbivorous mammals showing variable sagittal crest development across species, are ideal models for examining correlations between textural properties of food and sagittal crest morphology. Here, we integrate dietary data, dental microwear texture analysis, and finite element analysis to clarify the functional significance of the sagittal crest in tapirs. Most notably, pronounced sagittal crests are negatively correlated with hard-object feeding in extant, and several extinct, tapirs and can actually increase stress and strain energy. Collectively, these data suggest that musculature associated with pronounced sagittal crests—and accompanied increases in muscle volume—assists with the processing of tough food items in tapirs and may yield similar benefits in other mammals including early hominins.

Buccal dental-microwear and feeding ecology of Early Pleistocene Theropithecus oswaldi from Cueva Victoria (Spain)

Despite the scarcity of fossil specimens of Theropithecus oswaldi in Eurasia, its presence out of Africa attests to the great dispersal of this Papionini genus during the Early Pleistocene. In the present study, we analyze the buccal dental microwear of T. oswaldi (T. o. leakeyi) fossil specimens from Cueva Victoria (Southeastern Spain). This analysis is the first characterization of the feeding ecology of T. oswaldi in Europe. The buccal microwear pattern of the molar and premolar teeth of T. oswaldi from Cueva Victoria shows great similarities to that observed for the extant frugivorous forest-dwelling Mandrillus sphinx and mangabeys (Cercocebus sp.)-both species adapted to durophagous dietary habits-while significantly different from that observed for the gramnivorous Theropithecus gelada. These results suggest that T. oswaldi from Cueva Victoria could have exploited both hard-shelled fruits or seeds and succulent fruits from open and forested Mediterranean ecosystems.

Age-related tooth wear in African rainforest hunter-gatherers

OBJECTIVES

Central African small-scale foragers subsist primarily on hunting game activities and wild plant-food gathering. Starch-rich tubers are underground storage organs (USOs) and staple food resources in savanna and tropical rainforests. However, little is known about the effect of USO consumption on tooth wear development in living hunter-gatherers. We report age- and sex-dependent tooth wear rates in forest-dwelling Baka Pygmies with well-documented wild-yam-tuber-based diet to explore the long-term impact of USO mechanical hardness and abrasiveness on the wearing down of the teeth.

MATERIALS AND METHODS

Percentages of dentine exposure (PDEs) of permanent left mandibular first molars (M₁ ) were recorded using in vivo high-resolution replicas of Baka individuals (aged 8-33 years), inhabiting Le Bosquet district in Cameroon (Western Africa). Regression and covariance analyses were used to test the effect of individual aging by sex on PDE rates.

RESULTS

We found a strong increase of PDE by age among Baka individuals. No evidence of sexual dimorphism in wear patterns suggests similar sex-related dietary and masticatory demands during growth. Overall, greatest dentine exposure values ≈4% denote unexpected slow wear down rates for foraging diets relying on USO consumption.

DISCUSSION

The low molar wear rates with age found in Baka Pygmies contrast with extensive wear rates in savanna-dwelling foragers, reflecting differences in thermal processing techniques affecting fracture toughness and grittiness of mechanically challenging foods. Our findings reveal that culture-specific dietary proclivities influence tooth wear among foraging behaviors with important implications in hominin dietary versatility and abrasive stress on chewing surfaces.

Inference of Diets of Early Hominins from Primate Molar Form and Microwear

Paleontologists use fossil teeth to reconstruct the diets of early hominins and other extinct species. Some evidence is adaptive: nature selects for tooth size, shape, and structure best suited to specific food types. Other evidence includes traces left by actual foods eaten, such as microscopic tooth wear. This critical review considers how molars work, how they are used, and how occlusal topography and dental microwear can be used to infer diet and food preferences in the past, particularly for hominins of the Pliocene and early Pleistocene. Understanding that cheek teeth function as guides for chewing and tools for fracturing allows us to characterize aspects of occlusal form that reflect mechanical properties of foods to which a species is adapted. Living primates that often eat leaves, for example, have longer crests and more sloping occlusal surfaces than those that prefer hard foods. Studies of feeding ecology have shown, however, that tooth shape does not always correspond to preferred food items. It often follows mechanically challenging foods whether eaten often or rarely. Other lines of evidence that reflect actual tooth use are required to work out food preferences. Microwear textures, for example, reflect foods eaten by individuals in the past such that hard seeds and bone tend to leave complex, pitted surface textures, whereas tough leaves and meat more often leave anisotropic ones covered in long, parallel scratches. The study of fossil hominin molars shows how these various attributes are combined to infer diet and food preference in the past. A trend in occlusal morphology suggests decreased dietary specialization from Australopithecus to early Homo, and increasing dispersion in microwear complexity values is consistent with this. On the other hand, occlusal morphology may suggest dietary specialization in Paranthropus, although different species of this genus have different microwear texture patterns despite similar craniodental adaptations.

Buccal dental-microwear and dietary ecology in a free-ranging population of mandrills (Mandrillus sphinx) from southern Gabon

Analyses of dental micro- and macro-wear offer valuable information about dietary adaptations. The buccal surface of the teeth does not undergo attrition, indicating that dental microwear may directly inform about food properties. Only a few studies have, however, investigated the environmental and individual factors involved in the formation of such microwear in wild animals. Here, we examine variation of buccal microwear patterns of mandibular molars in a large free-ranging population of mandrills (Mandrillus sphinx). We first explore the influence of seasonality and individual's sex, age and tooth macrowear-expressed as the percent of dentine exposure (PDE)-on six microwear variables. Second, we analyze the interplay between individual's diet and PDE. In a last analysis, we revisit our results on mandrills in the light of other primate's microwear studies. We show that the average buccal scratch length and the frequency of vertical buccal scratches are both higher during the long dry season compared to the long rainy season, while we observe the inverse relationship for disto-mesial scratches. In addition, females present more disto-mesial scratches than males and older individuals present higher scratch density, a greater proportion of horizontal scratches but a lower proportion of vertical scratches than young animals. PDE yields similar results than individual's age confirming earlier results in this population on the relationship between age and tooth macrowear. Because seasonality and individual characteristics are both known to impact mandrills' diet in the study population, our results suggest that buccal microwear patterns may inform about individual feeding strategies. Furthermore, PDE increases with the consumption of potentially abrasive monocotyledonous plants, independently of the individuals' age, although it is not affected by food mechanical properties. Finally, buccal scratch densities by orientation appear as relevant proxies for discriminating between different primate taxa.

Buccal dental microwear texture and catarrhine diets

OBJECTIVES

Two-dimensional dental microwear analyses on occlusal and nonocclusal enamel surfaces have been widely applied to reconstruct the feeding behaviors of extant primates and to infer ecological adaptations in fossil hominins. To date, analyses of dental microwear texture, using three-dimensional, Scale-Sensitive Fractal Analysis approaches has only been applied to occlusal surfaces. Here, for the first time, we apply this 3D proxy to buccal enamel surfaces of catarrhine primates of known feeding ecologies to assess the utility of nonocclusal microwear texture variables as indicators of dietary habits.

MATERIALS AND METHODS

Buccal microwear texture attributes were collected from high-resolution second molar casts in a sample of seven extant African catarrhine taxa with differing dietary behaviors. A white-light confocal microscope with a 100× objective lens was used to record six microwear texture variables that assess complexity, anisotropy, heterogeneity, and textural fill volume.

RESULTS

The physical properties and variation in hardness of ingested foods is reflected by significant differences in the microwear variables on buccal enamel surfaces between species, which is in agreement with early reports using 2D microwear signatures of the same samples. Species that consume hard brittle items showed high buccal enamel complexity and low anisotropy values, while folivorous species that consume tough foods revealed high anisotropy and low complexity enamel patterns.

DISCUSSION

Buccal microwear texture analysis on enamel surfaces clearly reflects diet-related variation in nonhuman primates. Our findings indicate that microwear texture attributes on nonworking enamel surfaces provide an alternative procedure for reconstructing dietary behavior when wear facets on occlusal surfaces are lacking.