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Biomedical subjects

E R Dumont

Publications and source records attributed to E R Dumont.

7 recordsLinked to original sources
PubMed1997

Cranial shape in fruit, nectar, and exudate feeders: implications for interpreting the fossil record.

At least 29 species of fossil primates have been referred to fruit, nectar, and/or exudate feeding dietary niches. Many studies have detailed the morphological correlates of fruit feeding in comparison to insectivory and folivory. In contrast, few studies have sought to differentiate the morphological correlates of fruit feeding from those of nectar and exudate feeding. This study investigates the differences between fruit, nectar, and exudate feeders using 22 cranial and dentary shape variables representing 28 species of living marsupials, bats, and primates. Discriminant function analysis is used to investigate the differences between these dietary categories using both the complete data set and a reduced data set composed of variables that might reasonably be available from fragmentary fossil material. The success rates of post-hoc classifications are 94 and 88%, respectively. These results demonstrate that it is possible to discriminate among fruit, nectar, and exudate feeders among fossil taxa with a reasonable degree of certainty using the data and techniques outlined here. Nectar feeders exhibit a unique combination of features that are associated with reduced masticatory strength and their role as pollination agents. Exudate feeder skulls and dentaries exhibit a combination of features that reflect the high stresses encountered by the anterior dentition through bark gouging behavior. Fruit feeders are morphologically diverse, exhibiting cranial and mandibular shape values that overlap with both nectar and exudate feeders. It is suggested that this diversity reflects the variety of physical properties represented among fruits, and the tendency for individual frugivore species to specialize on particular fruits.

Animals↗
PubMed1996

Variation in quantitative measures of enamel prisms from different species as assessed using confocal microscopy.

This study presents a statistical analysis of variability in six measures of enamel prism and ameloblast size and spacing gathered using confocal microscopy, and applies the results to a consideration of appropriate sampling strategies for taxonomic analyses. Variability within individuals was examined within depth series. Individual variability was also assessed within a nested analysis of variation for prism measurements between micrographs, specimens and species. While sample depth was not often significantly associated with differences in prism and ameloblast measures, there was significant variation between micrographs taken from the same region of a tooth. The highest levels of variation were found between species, while variation between conspecific individuals was relatively small. These results demonstrate that data gathered from several micrographs are likely to be representative of a specimen, but that several micrographs of a single specimen will rarely illustrate the range of variation contained within a species. It is essential for systematic and taxonomic analyses that several micrographs be used to characterize an individual. It is also recommended that samples from several individuals be used to characterize species. While data from isolated specimens is often of great interest, taxonomic or systematic conclusions based on isolated individuals should be approached cautiously.

Animals↗
PubMed1996

Enamel prism morphology in molar teeth of small eutherian mammals.

Data summarizing enamel prism shape, size and spacing are reported for the molar enamel of 55 species of small eutherian mammals including primates, bats, tree shrews, flying lemurs, insectivorans and representatives of a variety of fossil families. Confocal photomicrographs reveal that the subsurface enamel of most species is characterized by arc-shaped prisms. The lack of a clear distinction between pattern 2 and pattern 3 prism configurations within single specimens suggests that the broad category "arc-shaped prisms" is the most appropriate descriptive grouping for these species. Of the total sample, three species exhibit only circular prisms while no evidence of prismatic enamel was found in two bats. Prism shape is not an informative phylogenetic character at the ordinal level for these morphologically primitive and relatively thin-enameled taxa. Significant differences between species in several prism size and spacing variables (central distance between prisms, prism diameter, prism area and the ratio of prism area to estimated ameloblast area) suggest the potential for further analyses of quantitative variation to document evolutionary relationships within or among family-level groups.

Animals↗
PubMed1995

The effects of sectioning angle on measurements of enamel prism size and spacing.

Comparative studies of prism size and spacing employ variables that are based on idealized, two-dimensional models. Results of modelling experiments illustrate that three-dimensional prism orientation can have a significant impact on two-dimensional measurements. In comparing prism size and spacing variables, it is essential to maintain control over the angle at which prisms are sectioned in order to compare real differences between taxa rather than preparation artefact. The further sectioning angles are from orthogonal, the greater the possibility for misrepresenting true prism size and spacing. While the survey of prism compression/extension (k) values reported here, as well as those described in previous studies, indicate that prism sectioning angles are only rarely extreme enough to render other values of prism and ameloblast size and spacing useless, the potential influence of sectioning obliquity on variation cannot be dismissed.

Ameloblasts↗
PubMed1995

Mammalian enamel prism patterns and enamel deposition rates.

Enamel prism patterns and enamel deposition rates were compared for specimens representing six mammalian orders. Enamel samples were characterized by either pattern 1 or pattern 3 prisms. Each prism pattern category contained prisms from at least two mammalian orders. Enamel deposition rate was estimated for each sample by measuring prism cross striation repeat intervals. Statistical analysis of cross striation repeat intervals illustrates significant differences in deposition rate between prism patterns 1 and 3. No statistically significant differences were found in deposition rate between the higher-level taxa represented within each prism pattern category. That enamel deposition rate is not taxonspecific reinforces the close association between deposition rate and prism morphology. In accord with previous studies, pattern 1 enamel is deposited more slowly than is pattern 3 enamel. Correlation analyses illustrated a lack of association between enamel deposition rate and body mass, tooth size, and estimated ameloblast size. Evidence that enamel deposition rate is associated with enamel prism morphology, coupled with evidence that deposition rate is not correlated with size parameters, points to developmental homology (i.e., homogeneous deposition rate) within each prism pattern.

Animals↗
PubMed1986

Mid-facial tissue depths of white children: an aid in facial feature reconstruction.

Available facial tissue thickness standards for facial feature reconstruction are based on adult measurements. Mid-facial tissue thicknesses for male and female white adolescents are presented here. Measurements were taken from lateral radiographs produced in an orthodontic practice. Statistical analysis indicates that age, sex, and to some extent, dental occlusion pattern are factors that should be taken into account when attempting facial feature reconstructions.

Adolescent↗