Dental microwear analysis in mammals: Teeth, diet and ecology

Abstract

Animal dental microwear texture analysis addresses relationships between dental texture and diet. The process is helpful in identifying diet preferences in mammals and may be useful for studies of paleoenvironment and climate change. Dental microwear texture on tooth enamel surfaces results from food consumption on short timescales and thus contains information about food and environment over a timeframe of days to weeks. Approximately 500 papers on dental microwear texture analysis have been published since 1978, and the number of publications has increased dramatically since 2002 when new methods and proxies were proposed to summarize microwear texture. Applications of dental microwear texture analysis are mainly for primates and humans in their first 20 years, but the methods are widely used for other mammals, such as ungulates, proboscides, carnivores, and rodents. To date, four different sets of proxies have been used to explain dental microwear texture. Two are 2D dental microwear analyses based on scanning electron microscope (SEM) or low magnification light microscope photomicrographs (LDM) to assess numbers and proportions of pits and scratches. The other two are 3D analyses based on light confocal microscopy and use of scale-sensitive fractal analysis (SSFA) or standard ISO surface texture parameters (STA). 3D methods are collectively called dental microwear texture analysis (DMTA). All four methods are effective in separating dietary categories in mammals although different methods are typically used for different mammalian groups. For example, in primates and humans, most research uses SEM and SSFA analyses, whereas in proboscides, over three-quarters of research uses LDM as the primary analysis method. Dental microwear texture analyses are widely used for identifying dietary categories in extant and fossil mammals, including ungulates, carnivores, rodents, primates, and even aquatic species. Both exogenous and endogenous factors contribute to dental abrasion, including phytolith, dust, enamel pieces, and water content. Tribological theory impacts of abrasive particles are debatable, but dental microwear analyses are empirically useful and are applied commonly in paleoecology. Diet identification is the most important and direct application of the method. Dietary categories are grazers, browsers, and mixed feeders for primates, ungulates, and proboscides. Categories for carnivores are omnivorous, carnivorous, and herbivorous. Combined diets of mammal fauna provide clues to ancient environmental conditions and are important in paleoecology reconstruction. Seasonal climate changes and climate events in the same or nearby areas might also be reflected in dental microwear analyses of mammal fauna. Dental microwear analyses could be used for identification of inter- and intra-specific dietary niches, distinguishing more subtle dietary differences among species, populations, age groups, and sexes. The accuracy of the 2D dental microwear analyses is sometimes questioned owing to measurement errors among different researchers and machines, especially in low magnification light microscope analysis. However, sampling procedures and the use of graphics software reduce errors and increase reliability. Dental microwear texture could differ in different teeth and enamel facets, but slight postmortem abrasive alteration does not change microwear texture features significantly. Multiproxies, such as dental microwear, dental mesowear, isotopes, and hypsodonty are used to evaluate more complicated cases and assess diet over different timescales.