Comparing Dirichlet normal surface energy of tooth crowns, a new technique of molar shape quantification for dietary inference, with previous methods in isolation and in combination (original) (raw)
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Dietary inference from dental topographic analysis of feeding tools in diverse animals
Methods in Ecology and Evolution, 2022
Understanding the relationship between form, function and diet in feeding structures is critical to constraining the roles of organisms in their ecosystem and adaptive responses to food resources. Yet, analysis of this relationship in invertebrates has been hampered by a reliance on descriptive and qualitative characterisation of the shapes of feeding structures. This has led to a lack of robust statistical analyses and overreliance on analogy and plausibility, especially for extinct taxa and animals that are hard to observe feeding. Here we test the efficacy of dental topographic metrics in quantification of form in invertebrate mandibles and assess their relationship with diet. Specifically, we analyse the mandibles of 45 species of extant orthopterans. Orthopterans' well‐constrained diets make them an ideal model system for our study. We find that topographic metrics applied to Orthoptera successfully recover the same relationship between dietary intractability and dental too...
J Hum Evol, 2005
A new method of scoring dental microscopic use wear, initially developed for and applied to extant and extinct ungulates, is here applied to primates, and the efficacy of the method as a tool for diagnosing diet in both ungulates and primates is established. The method employs standard refractive light microscopy instead of scanning electron microscopy (SEM), and all use-wear features are counted or scored under low magnification (35!). We use measurement systems analysis (variance components analysis of sources of measurement error) to evaluate the consistency and reproducibility of measurements using this method. The method is shown to have low intra-and interobserver measurement error, and to effectively distinguish among graminivores, folivores, and frugivores. It can also be used to identify seed predators and to diagnose hard-object feeding. The method is also shown to be robust to the selection of measurement site; it works equally well when applied to upper or to lower molars. Finally, we use analysis of variance to examine the consistency of the signals across mammalian orders, and discriminant function analysis to develop dietary diagnostic tools for a set of ''classified'' primates with known diets. We test the success of these tools not merely by examining their a posteriori classification ''success,'' but by using them to construct predicted dietary profiles for a sample of unclassified extant primate species, again with known diets.
The correlation between diet and dental topography is of importance to paleontologists seeking to diagnose ecological adaptations in extinct taxa. Although the subject is well represented in the literature, few studies directly compare methods or evaluate dietary signals conveyed by both upper and lower molars. Here, we address this gap in our knowledge by comparing the efficacy of three measures of functional morphology for classifying an ecologically diverse sample of thirteen medium-to large-bodied platyrrhines by diet category (e.g., folivore, frugivore, hard object feeder). We used Shearing Quotient (SQ), an index derived from linear measurements of molar cutting edges and two indices of crown surface topography, Occlusal Relief (OR) and Relief Index (RFI). Using SQ, OR, and RFI, individuals were then classified by dietary category using Discriminate Function Analysis. Both upper and lower molar variables produce high classification rates in assigning individuals to diet categories, but lower molars are consistently more successful. SQs yield the highest classification rates. RFI and OR generally perform above chance. Upper molar RFI has a success rate below the level of chance. Adding molar length enhances the discriminatory power for all variables. We conclude that upper molar SQs are useful for dietary reconstruction, especially when combined with body size information. Additionally, we find that among our sample of platyrrhines, SQ remains the strongest predictor of diet, while RFI is less useful at signaling dietary differences in absence of body size information. The study demonstrates new ways for inferring the diets of extinct platyrrhine primates when both upper and lower molars are available, or, for taxa known only from upper molars. The techniques are useful in reconstructing diet in stem representatives of anthropoid clade, who share key aspects of molar morphology with extant platyrrhines.
Dietary Inference from Upper and Lower Molar Morphology in Platyrrhine Primates
The correlation between diet and dental topography is of importance to paleontologists seeking to diagnose ecological adaptations in extinct taxa. Although the subject is well represented in the literature, few studies directly compare methods or evaluate dietary signals conveyed by both upper and lower molars. Here, we address this gap in our knowledge by comparing the efficacy of three measures of functional morphology for classifying an ecologically diverse sample of thirteen medium- to large-bodied platyrrhines by diet category (e.g., folivore, frugivore, hard object feeder). We used Shearing Quotient (SQ), an index derived from linear measurements of molar cutting edges and two indices of crown surface topography, Occlusal Relief (OR) and Relief Index (RFI). Using SQ, OR, and RFI, individuals were then classified by dietary category using Discriminate Function Analysis. Both upper and lower molar variables produce high classification rates in assigning individuals to diet categories, but lower molars are consistently more successful. SQs yield the highest classification rates. RFI and OR generally perform above chance. Upper molar RFI has a success rate below the level of chance. Adding molar length enhances the discriminatory power for all variables. We conclude that upper molar SQs are useful for dietary reconstruction, especially when combined with body size information. Additionally, we find that among our sample of platyrrhines, SQ remains the strongest predictor of diet, while RFI is less useful at signaling dietary differences in absence of body size information. The study demonstrates new ways for inferring the diets of extinct platyrrhine primates when both upper and lower molars are available, or, for taxa known only from upper molars. The techniques are useful in reconstructing diet in stem representatives of anthropoid clade, who share key aspects of molar morphology with extant platyrrhines.
Journal of Anatomy, 2008
This contribution investigates the evolution of diet in the Pan–Homo and hominin clades. It does this by focusing on 12 variables (nine dental and three mandibular) for which data are available about extant chimpanzees, modern humans and most extinct hominins. Previous analyses of this type have approached the interpretation of dental and gnathic function by focusing on the identification of the food consumed (i.e. fruits, leaves, etc.) rather than on the physical properties (i.e. hardness, toughness, etc.) of those foods, and they have not specifically addressed the role that the physical properties of foods play in determining dental adaptations. We take the available evidence for the 12 variables, and set out what the expression of each of those variables is in extant chimpanzees, the earliest hominins, archaic hominins, megadont archaic hominins, and an inclusive grouping made up of transitional hominins and pre-modern Homo. We then present hypotheses about what the states of these variables would be in the last common ancestor of the Pan–Homo clade and in the stem hominin. We review the physical properties of food and suggest how these physical properties can be used to investigate the functional morphology of the dentition. We show what aspects of anterior tooth morphology are critical for food preparation (e.g. peeling fruit) prior to its ingestion, which features of the postcanine dentition (e.g. overall and relative size of the crowns) are related to the reduction in the particle size of food, and how information about the macrostructure (e.g. enamel thickness) and microstructure (e.g. extent and location of enamel prism decussation) of the enamel cap might be used to make predictions about the types of foods consumed by extinct hominins. Specifically, we show how thick enamel can protect against the generation and propagation of cracks in the enamel that begin at the enamel–dentine junction and move towards the outer enamel surface.
Adaptive wear-based changes in dental topography associated with atelid (Mammalia: Primates) diets
Biological Journal of the Linnean Society
Primates are generally characterized by low-crowned, brachydont molars relative to many other groups of mammals. This conservative architecture may create special challenges for maintaining dental functionality in the case of a diet requiring proficient shearing ability (e.g. folivory). One recent hypothesis, the 'dental sculpting hypothesis', suggests that some folivorous primates have dentitions that functionally harness macrowear in maintaining occlusal sharpness. We examined the relationships between four dental topography metrics [Dirichlet normal energy (DNE), orientation patch count rotated (OPCR), relief index (RFI) and occlusal relief (OR)] against macrowear [as measured by the dentine exposure ratio (DER)] in lower first molars of Ateles and Alouatta, which are two closely related platyrrhines with different diets (Alouatta is a folivore and Ateles a frugivore). We find support for the dental sculpting hypothesis, in that DNE increases with macrowear in the folivorous Alouatta but not in the frugivorous Ateles. Multiple contradictions between OPCR and the other variables suggest that this metric is a poor reflection of the molar form-function relationship in these primates. Distributions of relief measures (RFI and OR) confound expectations and prior observations, in that Ateles shows higher values than Alouatta, because these measures are thought to be correlated with dental shearing ability. We discuss the role that the relatively thicker enamel caps of Ateles might play in the distributions of these metrics. ADDITIONAL KEYWORDS: dentine exposure ratio-Dirichlet normal energy-molaR-niche partitioningocclusal relief-orientation patch count rotated-relief index.
Tooth wear as a means to quantify intra-specific variations in diet and chewing movements
In mammals, tooth function, and its efficiency, depends both on the mechanical properties of the food and on chewing dynamics. These aspects have rarely been studied in combination and/or at the intra-specific level. Here we applied 3D dental surface texture analysis to a sample of field voles (Microtus agrestis) trapped from Finnish Lapland at different seasons and localities to test for inter-population variations. We also explored intra-individual variation in chewing dynamics by analysing two facets on the second upper molars. Our results confirm that the two localities have similar environments and that the voles feed on the same items there. On the other hand, the texture data suggest that diets are seasonally variable, probably due to varying concentrations of abrasives. Lastly, the textures on the buccal facets are more isotropic and their direction deviates more from the mesial chewing direction than the lingual facets. We interpret these results as reflecting food, rather than chewing, movements, where food particles are more guided on the lingual side of the molars. This has implications for the application of dental microwear analysis to fossils: only homologous facets can be compared, even when the molar row seems to constitute a functional unit. In mammals, teeth are essential to fracture food particles so that enzymes in the digestive track can efficiently extract nutrients. Tooth functionality, therefore, depends on (1) the biomechanical properties of ingesta and (2) the chewing dynamics, related to chewing movements and forces. Tooth function has been approached from three complementary lines of evidence: functional morphology 1,2 , dietary reconstructions 3,4 and reconstructions of chewing mechanics 5,6. It has been shown repeatedly 7 that tooth function cannot be reconstructed solely from the tooth morphology because the form only constraints what an animal can eat and because the actual function (what the animal ate) also depends on other ecological factors like food availability, competition and predation. Therefore, proxies independent of tooth form are required to reconstruct both diet and chewing mechanics. Intra-specific variations in tooth function remain understudied; yet, understanding how and how much tooth function varies intra-specifically, and even intra-individually, is essential to calibrate paleoenvironmental reconstructions based on dietary inferences at the inter-specific level, and to study micro-and macroevolution. Rodents represent an important part of the fossil record due to their abundance, ubiquity and diversity throughout the Cenozoic 8. Additionally, unlike large mammals, rodents are non-migratory and short-lived animals , which make them particularly useful in reconstructions of past climates at local and regional scales. Within rodents, Arvicolinae (voles and lemmings) constitute an excellent mammalian model group for biostratigraphy 9 and terrestrial paleoecological and paleoenvironmental reconstructions 10,11 , as well as for understanding the role of development in the evolution of tooth morphology 12,13. Although it is known from field observations that their diets and habitats are very diverse, arvicolines are usually regarded as grazers in open and cold paleoenviron-ments 14,15. This lack of precision precludes detailed local paleoenvironmental reconstructions. Arvicolines have characteristic prismatic and hypsodont (high crowned) or hypselodont (hypsodont and ever-growing) molars 16. Although the chewing dynamics of arvicolines seems to be quite simple, in which the whole flat molar row shears