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A first attempt to quantify dietary adaptations of carnivorous mammals using the Dirichlet normal energy of molar crowns
Abstract
The order Carnivora is comprised of a wide variety of taxa, which are adapted to differing amounts of meat intake (hypo-, meso- and hypercarnivores) and show a recurring pattern of convergent evolution of craniodental features, especially in molar morphology, in concurrence with their dietary adaptations. A further tendency of convergent evolution can be observed among carnivorous marsupials (Dasyuromorphia) and "creodonts" (Hyaenodonta). In this study, crown curvature measured as the Dirichlet normal surface energy (DNE) of 47 lower m1s of carnivorous taxa and additional distal molar positions of dasyuromorphs and hyaenodonts was calculated in order to quantify their dietary adaptations. Quantification of crown curvature by DNE alone seems to be insufficient for exact predictions about dietary adaptations in this sample of carnivorous mammals, although some correlations are evident. Very low energy values are a strong indicator of a hypercarnivorous diet, as the lowest values are present only in felids and in the dasyuromorph and hyaenodont m1. The highest values occur in Civettictis, Ichneumia and Ailurus. A distinction between meso- and hypocarnivorous diet is not possible, but there is a general tendency of increasing values from hypercarnivorous taxa on the low end of the spectrum to meso- and hypocarnivorous taxa on the high end. Dasyuromorphs and hyaenodonts both evolved carnassialization on all molar positions, with the m1 position generally showing lower DNE values than the most distal molar.
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Researchers studying mammalian dentitions from functional and adaptive perspectives increasingly have moved towards using dental topography measures that can be estimated from 3D surface scans, which do not require identification of specific homologous landmarks. Here we present molaR, a new R package designed to assist researchers in calculating four commonly used topographic measures: Dirichlet Normal Energy (DNE), Relief Index (RFI), Orientation Patch Count (OPC), and Orientation Patch Count Rotated (OPCR) from surface scans of teeth, enabling a unified application of these informative new metrics. In addition to providing topographic measuring tools, molaR has complimentary plotting functions enabling highly customizable visualization of results. This article gives a detailed description of the DNE measure, walks researchers through installing, operating, and troubleshooting molaR and its functions, and gives an example of a simple comparison that measured teeth of the primates Alouatta and Pithecia in molaR and other available software packages. molaR is a free and open source software extension, which can be found at the doi:10.13140/RG.2.1.3563.4961 (molaR v. 2.0) as well as on the Internet repository CRAN, which stores R packages.
Dental topographic analysis is the quantitative assessment of shape of three-dimensional models of tooth crowns and component features. Molar topographic curvature, relief, and complexity correlate with aspects of feeding behavior in certain living primates, and have been employed to investigate dietary ecology in extant and extinct primate species. This study investigates whether dental topography correlates with diet among a diverse sample of living platyrrhines, and compares platyrrhine topography with that of prosimians. We sampled 111 lower second molars of 11 platyrrhine genera and 121 of 20 prosimian genera. For each tooth we calculated Dirichlet normal energy (DNE), relief index (RFI), and orientation patch count (OPCR), quantifying surface curvature, relief, and complexity respectively. Shearing ratios and quotients were also measured. Statistical analyses partitioned effects of diet and taxon on topography in platyrrhines alone and relative to prosimians. Discriminant function analyses assessed predictive diet models. Results indicate that platyrrhine dental topography correlates to dietary preference, and platyrrhine-only predictive models yield high rates of accuracy. The same is true for prosimians. Topographic variance is broadly similar among platyrrhines and prosimians. One exception is that platyrrhines display higher average relief and lower relief variance, possibly related to lower relative molar size and functional links between relief and tooth longevity distinct from curvature or complexity. Explicitly incorporating phylogenetic distance matrices into statistical analyses of the combined platyrrhine-prosimian sample results in loss of significance of dietary effects for OPCR and SQ, while greatly increasing dietary significance of RFI. Am J Phys Anthropol 153:29-44, 2014. © 2013 Wiley Periodicals, Inc.
Inferred dietary preference is a major component of paleoecologies of extinct primates. Molar occlusal shape correlates with diet in living mammals, so teeth are a potentially useful structure from which to reconstruct diet in extinct taxa. We assess the efficacy of Dirichlet normal energy (DNE) calculated for molar tooth surfaces for reflecting diet. We evaluate DNE, which uses changes in normal vectors to characterize curvature, by directly comparing this metric to metrics previously used in dietary inference. We also test whether combining methods improves diet reconstructions. The study sample consisted of 146 lower (mandibular) second molars belonging to 24 euarchontan taxa. Five shape quantification metrics were calculated on each molar: DNE, shearing quotient, shearing ratio, relief index, and orientation patch count rotated (OPCR). Statistical analyses were completed for each variable to assess effects of taxon and diet. Discriminant function analysis was used to assess ability of combinations of variables to predict diet. Values differ significantly by diets for all variables, although shearing ratios and OPCR do not distinguish statistically between insectivores and folivores or omnivores and frugivores. Combined analyses were much more effective at predicting diet than any metric alone. Alone, relief index and DNE were most effective at predicting diet. OPCR was the least effective alone but is still valuable as the only quantitative measure of surface complexity. Of all methods considered, DNE was the least methodologically sensitive, and its effectiveness suggests it will be a valuable tool for dietary reconstruction.