Browsing by Subject "DNE"
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Item Open Access Dental Ecometrics as a Proxy of Paleoenvironment Reconstruction in the Miocene of South America(2017) Spradley, Jackson PlesIn this dissertation I compile modern mammalian faunal lists, as well as ecomorphological measurements on living marsupials and rodents, to relate the diversity of small mammals, specifically the distributions of their dental topographies, to the climates in which they are found. The emphasis of this dissertation is to demonstrate the potential of distributions of dental topography metrics as proxies for the reconstruction of paleoenvironments in the Miocene of South America.
In Chapter 2, I compile complete, non-volant mammalian species lists for 85 localities across South America as well as 17 localities across Australia and New Guinea. Climatic and habitat variables were also recorded at each locality using GIS spatial data. Additionally, basic ecological data was collected for each species, including: diet, body size, and mode of locomotion. Niche indices that describe the relative numbers of different ecologies were calculated for each locality. These indices then served as the predictor values in a handful of regression models, including regression trees, random forests, and Gaussian process regression. The Australian/New Guinean localities were used as a geographically and phylogenetically independent for the purposes of testing the models derived from South America.
As for the dental ecomorphological analysis, I use three separate measures of dental topography, each of which measures a different component of dental topography; relief (the Relief Index, or RFI), complexity (orientation patch count rotated, OPCR), and sharpness (Dirichlet normal energy, DNE). Together, these metrics quantify the shape of the tooth surface without regard for tooth size. They also do not depend on homologous features on the tooth surface for comparative analysis, allowing a broad taxonomic sample as I present here. After a methodological study of DNE in Chapter 3, I present correlative studies of dental topography and dietary ecology in marsupials and rodents in Chapters 4 and 5, respectively. Finally, using the same localities from Chapter 2, I analyze the distributions of dental topography metrics as they relate to climate and habitat.
Results suggest that sharpness and relief are positively correlated with a higher amount of tough foods—such as leaves or insects—in the diet of marsupials, and that relief is positively correlated with grass-eating in rodents. The distributions of all three metrics show some utility when used as a proxy for climatic variables, though the distributions of RFI in marsupials and OPCR in rodents demonstrate the best correlations.
Overall, this dissertation suggests that dental topography can be used to discriminate dietary categories in a wide variety of mammalian groups, and that the distributions of dental ecometrics can be used as proxies for paleoenvironment reconstruction. This may eliminate the need to reconstruct behavior in individual taxa in order to construct ecological indices for fossil mammalian communities, thus offering a more direct avenue to reconstructing past environments.
Item Open Access Dental topography of the Oligocene anthropoids Aegyptopithecus zeuxis and Apidium phiomense: Paleodietary insights from analysis of wear series.(Journal of human evolution, 2023-05) Morse, Paul E; Pampush, James D; Kay, Richard FFossil primate dietary inference is enhanced when ascertained through multiple, distinct proxies. Dental topography can be used to assess changes in occlusal morphology with macrowear, providing insight on tooth use and function across the lifespans of individuals. We measured convex Dirichlet normal energy-a dental topography metric reflecting occlusal sharpness of features such as cusps and crests-in macrowear series of the second mandibular molars of two African anthropoid taxa from ∼30 Ma (Aegyptopithecus zeuxis and Apidium phiomense). Wear was quantified via three proxies: occlusal dentine exposure, inverse relief index, and inverse occlusal relief. The same measurements were calculated on macrowear series of four extant platyrrhine taxa (Alouatta, Ateles, Plecturocebus, and Sapajus apella) to provide an analogical framework for dietary inference in the fossil taxa. We predicted that Ae. zeuxis and Ap. phiomense would show similar patterns in topographic change with wear to one another and to extant platyrrhine frugivores like Ateles and Plecturocebus. The fossil taxa have similar distributions of convex Dirichlet normal energy to one another, and high amounts of concave Dirichlet normal energy 'noise' in unworn molars-a pattern shared with extant hominids that may distort dietary interpretations. Inverse relief index was the most useful wear proxy for comparison among the taxa in this study which possess disparate enamel thicknesses. Contrary to expectations, Ae. zeuxis and Ap. phiomense both resemble S. apella in exhibiting an initial decline in convex Dirichlet normal energy followed by an increase at the latest stages of wear as measured by inverse relief index, lending support to previous suggestions that hard-object feeding played a role in their dietary ecology. Based on these results and previous analyses of molar shearing quotients, microwear, and enamel microstructure, we suggest that Ae. zeuxis had a pitheciine-like strategy of seed predation, whereas Ap. phiomense potentially consumed berry-like compound fruits with hard seeds.Item Open Access Sign-oriented Dirichlet Normal Energy: Aligning Dental Topography and Dental Function in the R-package molaR(Journal of Mammalian Evolution, 2022-12-01) Pampush, JD; Morse, PE; Fuselier, EJ; Skinner, MM; Kay, RFDirichlet normal energy (DNE) is a dental topography measurement aimed at capturing occlusal sharpness and has shown promise for its ability to sort primate molars according to perceived shearing ability. As initially implemented, this measurement does not differentiate concave versus convex contributions to surface sharpness. This is problematic because the DNE-signal derived from concave aspects of an occlusal surface measures a sharp ‘edge’ oriented inward towards the enamel dentine junction rather than outward towards food contact. The inclusion of concave DNE in dietary analyses of molars possessing deep occlusal sulci–such as those found among hominoids–inflates the perceived functional sharpness of these teeth. Concave-inflated DNE values can be misleading, being interpreted as indicating that a particular taxon is more adapted for processing fibrous food than is warranted. The modification of the DNE measurement introduced here ‘Sign-oriented DNE’ alleviates this problem by elimination of concave sharpness from analyses, allowing investigations to focus on features of occlusal surfaces plausibly linked to shearing, cutting, or shredding of food materials during Phases I and II of the masticatory power stroke. Convex DNE is just as effective at sorting non-hominoid primate molars into traditional dietary categories as the initial applications of the orientation-blind version of the measurement, and produces more theoretically coherent results from hominoid molars. Focusing on- and improving the connection between measurement and occlusal function will enhance the ability of dental topography to make meaningful contributions to our collective understanding of species’ dietary ecologies.