Tooth Form and Function: Insights into Adaptation through the Analysis of Dental Microwear

Department of Anthropology, University of Arkansas, Fayetteville, AR 72701, USA.
Frontiers of oral biology 09/2009; 13:38-43. DOI: 10.1159/000242388
Source: PubMed


Mammalian molar form is clearly adapted to fracture foods with specific material properties. Studies of dental functional morphology can therefore offer important clues about the diets of fossil taxa. That said, analyses of tooth form provide insights into ability to fracture resistant foods rather than the food preferences of individuals. Recent work suggests that specialized occlusal morphology can relate to either preferred foods, or to occasionally eaten fallback items critical for survival. This paper reviews dental microwear texture analysis, a new approach that can be used to infer fracture properties of foods eaten in life. High-resolution 3D point clouds of microwear surfaces are collected and analyzed using scale-sensitive fractal analyses. Resulting data are free from operator measurement error, and allow the characterization and comparison of within-species variation in microwear texture attributes. Examples given here include four extant primate species (two folivores and two hard object fallback feeders), and two fossil hominin taxa. All groups show at least some individuals with simple microwear surfaces that suggest a lack of consumption of hard and brittle abrasive foods during the last few meals. On the other hand, some hard object fallback specimens have very complex surfaces consistent with consumption of hard, brittle foods. The latter pattern is also found in one hominin species. These results suggest that dental microwear texture analysis can help us determine whether craniodental specializations in fossil species are adaptations to preferred foods, or to less often but still critical fallback items.

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    • "The mammalian dentition represents a direct interaction between an individual and its environment. It has been well-established in extant primates that macroand micro-dental form can be reflective of a number of these interactions, including overall dietary niche and foraging behavior, allowing dietary inferences about extinct primates (Gregory, 1922; Hylander, 1975; Kay, 1975; Covert, 1986; Rosenberger, 1992; Anapol and Lee, 1994; Teaford, 2000; Bunn and Ungar, 2009; Ungar, 2009; White et al., 2009; Daegling et al., 2011, 2013; Cuozzo et al., 2012; Klukkert et al., 2012; Scott et al., 2012; Ross and Iriarte-Diaz, 2014; Winchester et al., 2014; Deane, 2015). However, the majority of these studies has been conducted on anthropoids and has focused primarily on frugivory and folivory as dietary niches. "
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    ABSTRACT: Slow lorises (Nycticebus spp.) are obligate exudativores that gouge tree bark. Dental adaptations for gouging within marmosets, the only other known primate obligate exudativore, are well-known but dental adaptations in Nycticebus are largely unidentified. In an effort to more completely understand potential dental adaptions within Nycticebus and the evolution of this dietary niche within Primates as an order, the present study examined dental morphometrics in the Asian lorises (Nycticebus and Loris). We compared dental morphometrics between Nycticebus and the insectivorous slender lorises (Loris). Measurements from the toothcomb and select other teeth were taken from 92 specimens. Each variable was scaled by the geometric mean and resulting mean ratios were statistically compared between groups. A biomechanical shape variable was also calculated to estimate the ability of the toothcomb to resist bending that may be experienced during gouging. Toothcombs in Nycticebus were significantly (P < 0.05) more narrow, shorter, and thicker than those in Loris and had a higher calculated ability to withstand bending forces. Nycticebus also had reduced size in the last lower molar relative to Loris. The more robust, “squared off” toothcomb in Nycticebus matches behavioral observations that these primates gouge to access exudates. Results of the present study indicate that the toothcomb is the likely candidate for the dental tool used in gouging. The size reduction of the lower last molar in Nycticebus, a trait also found in a previous study in exudativorous galagos, may indicate that there is reduced selective pressure in a diet where little mastication would be needed to mechanically process exudates. These results may indicate that reduction in molar size could be a potential dental signature for exudativory, but further studies on a wider phylogenetic range of exudativorous primates would be necessary. Am J Phys Anthropol, 2015.
    Full-text · Article · Aug 2015 · American Journal of Physical Anthropology
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    • "The field was systematized by the work of Ungar (2007, 2009, Ungar & Kay 1995) and by Teaford (1988, 1991, 1994). The significance of grit or dust particles taken up with food items has been described by Ungar (2009) and more particularly by Damuth and Janis (2011) and Strait et al. (2012). More recently, Scott et al. (2012) isolated four microwear parameters and analyzed a range of living monkeys and apes, confirming that microwear textures vary with diet in primates. "
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    ABSTRACT: Four types of taxon-free analysis of mammalian faunas are discussed to come to an understanding of the degree to which they are independent of taxonomy. Species richness patterns and size distributions of faunal assemblages provide general indications of palaeoecology and are based entirely on species identifications; ecomorphology targets specific taxonomic groups, but within the group it is partly independent of taxonomy; community ecology describes mammalian communities by their levels of diversity within distinct ecological categories rather than by their species, and two approaches are based either on qualitative evidence (ecological diversity) or on quantitative evidence, combining ecomorphological data for whole communities (community ecomorphology). No method is entirely taxon-free, but all have stronger ecological foundations than methods based on linking fossil species of unknown habitat with their supposed habitats based on their relationships with their living relatives.
    Full-text · Article · Apr 2014 · Annales Zoologici Fennici
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    • "). Because they are important to the survival of the animal during these periods, fallback foods may be just as influential to primate molar form as preferred foods, or more so, even though they are eaten less often during the year (Rosenberger and Kinzey, 1976; Kinzey, 1978; Rosenberger, 1992; Marshall and Wrangham, 2007; Ungar, 2009). In chimpanzee populations, the specific types and proportions of these resources may be highly variable (Morgan and Sanz, 2006). "
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    ABSTRACT: Molar tooth morphology is generally said to reflect a compromise between phylogenetic and functional influences. Chimpanzee subspecies have been reported to exhibit differences in molar dimensions and nonmetric traits, but these have not been related to differences in their diets. And in fact, observations to date of the diets of chimpanzees have not revealed consistent differences among subspecies. This study uses dental topographic analyses shown to reflect diet-related differences in occlusal morphology among primate species, to assess within-species variation among chimpanzee subspecies. High-resolution casts from museum collections were examined by laser scanning, and resulting data were analyzed using GIS algorithms and a two-factor ANOVA model. Although differences were noted between wear stages within subspecies in surface slope, relief, and angularity, none were found to distinguish the subspecies from one another in these attributes. This might reflect limitations in the ability of this method to detect diet-related differences, but is also consistent with a lack of differences in functionally relevant aspects of occlusal morphology among chimpanzee subspecies.
    Full-text · Article · Jun 2012 · American Journal of Physical Anthropology
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