Earth Sciences Faculty Works

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Browsing Earth Sciences Faculty Works by Author "Davis, Edward Byrd"

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    Are Hypsodonty and Occlusal Enamel Complexity Evolutionarily Correlated in Ungulates?
    (Journal of Mammalian Evolution, Springer Link, 2015-05-13) Famoso, Nicholas; Davis, Edward Byrd; Feranec, Robert S.; Hopkins, Samantha S. B.; Price, Samantha A.
    The spread of grasslands and cooling climate in the Miocene contributed to an increasingly abrasive diet for ungulates. This increase in abrasiveness is proposed to select for both hypsodonty and increasing complexity of occlusal enamel bands. If these traits evolved in response to strong selection to resist tooth wear while feeding in grassland habitats, we might expect them to have evolved in a correlated fashion. If, on the other hand, there was a developmental or physiological constraint, or if selection was not strong on total enamel production, we would expect species to have evolved one or the other of these traits at a time, producing an uncorrelated, or even inversely correlated, pattern of trait evolution. To test these hypotheses, we examined the Occlusal Enamel Index (OEI) and Hypsodonty Index (HI) of 773 ungulate teeth. We tested the dependence of OEI on HI for the orders Artiodactyla and Perissodactyla using phylogenetic generalized least squares regression (PGLS). The two traits are not significantly correlated in the PGLS, for Artiodactyla and Perissodactyla. Despite their physical proximity, close functional utility, and conventional correlation, our results reject the hypothesis that HI and OEI are evolutionarily linked in these lineages, suggesting that selection to resist tooth wear was not so strong as to drive the overall evolutionary trajectory of both these traits at the same time.
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    First mesonychid from the Clarno Formation (Eocene) of Oregon, USA
    (Palaeontologia Electronica, 2019-06) Robson, Selina V.; Famoso, Nicholas; Davis, Edward Byrd; Hopkins, Samantha S.B.
    A recently identified left dentary of Harpagolestes cf. uintensis represents the first mesonychid material known from the Pacific Northwest. The specimen is from the Hancock Quarry (Clarno Unit, John Day Fossil Beds National Monument), which is in the uppermost subunit of the Clarno Formation (middle Eocene, ~40 Ma). The sediments of the Hancock Quarry were deposited by a meandering river system during the middle Eocene when north-central Oregon had a subtropical climate. As with many other mammals from the Hancock Quarry, Harpagolestes participated in an Asian-North American faunal interchange; species of Harpagolestes are known from the Eocene of both continents. Harpagolestes was carnivorous, and members of the genus were likely bone-crushers. Characteristic bone-crushing wear is visible on the occlusal surfaces of the Hancock Quarry specimen’s premolars and molars. With the aid of CT scans, it has been determined that the Hancock Quarry Harpagolestes contains the alveoli for c1, p1-2, and m3, and preserves the crowns of p3-4 and m1-2. The molariform teeth have a large, conical trigonid with a bulbous talonid. The protoconid of p3 and p4 is tilted posteriorly. This specimen of Harpagolestes cf. uintensis represents a new large carnivore in the Hancock Quarry ecosystem, adds to the known diversity of the Oregon middle Eocene, and is the only known occurrence of a mesonychid in the Pacific Northwest.
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    How do diet and body mass drive reproductive strategies in mammals?
    (Biological Journal of the Linnean Society, 2018-04-19) Famoso, Nicholas; Hopkins, Samantha S.B.; Davis, Edward Byrd
    Larger body size tends to lead to lower reproductive rates in mammals, but we do not understand how diet impacts this relationship. Reproductive strategies vary from K-selected (producing few offspring with extensive parental care) to r-selected (producing many offspring with little parental care). Here, we investigate how diet and body size impact the reproductive strategies of mammals within a phylogenetic framework using an index for reproductive strategy. For all diet categories we find larger mammals to be more K-selected. This relationship is significant for herbivores and omnivores, but not for carnivores, although the relationship for carnivores is comparable to that of herbivores and omnivores. The relationship is non-linear in carnivores and may be a consequence of differences between insect and vertebrate predators. Ultimately, the trend of more K-selected strategies with larger body size holds true for herbivores and omnivores, but different trajectories exist for carnivores depending on diet.
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    Morphological Proxies for Fossoriality, Supplementary Appendices
    (2009-08-20T17:10:34Z) Hopkins, Samantha; Davis, Edward Byrd
    Supplementary Appendices from Hopkins and Davis 2009, Journal of Mammalogy. Appendix I: Taxonomy, ecological data, and morphological characters from 123 species representing 15 of the 29 orders of extant mammals, used for discriminant analysis. Appendix II: Eigenvectors from discriminant analyses.
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    Occlusal Enamel Complexity in Middle Miocene to Holocene Equids (Equidae: Perissodactyla) of North America
    (PLOSone, 2014-02-27) Famoso, Nicholas; Davis, Edward Byrd
    Four groups of equids, “Anchitheriinae,” Merychippine-grade Equinae, Hipparionini, and Equini, coexisted in the middle Miocene, but only the Equini remains after 16 Myr of evolution and extinction. Each group is distinct in its occlusal enamel pattern. These patterns have been compared qualitatively but rarely quantitatively. The processes influencing the evolution of these occlusal patterns have not been thoroughly investigated with respect to phylogeny, tooth position, and climate through geologic time. We investigated Occlusal Enamel Index, a quantitative method for the analysis of the complexity of occlusal patterns. We used analyses of variance and an analysis of co-variance to test whether equid teeth increase resistive cutting area for food processing during mastication, as expressed in occlusal enamel complexity, in response to increased abrasion in their diet. Results suggest that occlusal enamel complexity was influenced by climate, phylogeny, and tooth position through time. Occlusal enamel complexity in middle Miocene to Modern horses increased as the animals experienced increased tooth abrasion and a cooling climate.
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    On the relationship between enamel band complexity and occlusal surface area in Equids (Mammalia, Perissodactyla)
    (PeerJ, 2016-07) Famoso, Nicholas; Davis, Edward Byrd
    Enamel patterns on the occlusal surfaces of equid teeth are asserted to have tribal-level differences. The most notable example compares the Equini and Hipparionini, where Equini have higher crowned teeth with less enamel-band complexity and less total occlusal enamel than Hipparionini. Whereas previous work has successfully quantified differences in enamel band shape by dividing the length of enamel band by the square root of the occlusal surface area (Occlusal Enamel Index, OEI), it was clear that OEI only partially removes the effect of body size. Because enamel band length scales allometrically, body size still has an influence on OEI, with larger individuals having relatively longer enamel bands than smaller individuals. Fractal dimensionality (D) can be scaled to any level, so we have used it to quantify occlusal enamel complexity in a way that allows us to get at an accurate representation of the relationship between complexity and body size. To test the hypothesis of tribal-level complexity differences between Equini and Hipparionini, we digitally traced a sample of 98 teeth, one tooth per individual; 31 Hipparionini and 67 Equini. We restricted our sampling to the P3-M2 to reduce the effect of tooth position. After calculating the D of these teeth with the fractal box method which uses the number of boxes of various sizes to calculate the D of a line, we performed a t -test on the individual values of D for each specimen, comparing the means between the two tribes, and a phylogenetically informed generalized least squares regression (PGLS) for each tribe with occlusal surface area as the independent variable andDas the dependent variable. The slopes of both PGLS analyses were compared using a t -test to determine if the same linear relationship existed between the two tribes. The t -test between tribes was significant (p<0:0001), suggesting differentDpopulations for each lineage. The PGLS for Hipparionini was a positive but not significant (pD0:4912) relationship between D and occlusal surface area, but the relationship for Equini was significantly negative (p D 0:0177). was 0 for both tests, indicating no important phylogenetic signal is present in the relationship between these two characters, thus the PGLS collapses down to a non-phylogenetic generalized least squares (GLS) model. The t -test comparing the slopes of the regressions was not significant, indicating that the two lineages could have the same relationship between D and occlusal surface area. Our results suggest that the two tribes have the same negative relationship between D and occlusal surface area but the Hipparionini are offset to higher values than the Equini. This offset reflects the divergence between the two lineages since their last common ancestor and may have constrained their ability to respond to environmental change over the Neogene, leading to the differential survival of the Equini.