Evolving entities in fossil populations: A morphometric analysis of Miocene planktonic foraminifera (Globorotalia).
The choice of a classification scheme is based both on the variance within categories and the discontinuities between categories. This leads to difficulties in classifying biologic taxa that exhibit continuous morphological variation. But, although complete discontinuities in variation are rare, the...
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| Other Authors: | , |
| Format: | Thesis |
| Language: | English |
| Published: |
1988
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| Online Access: | https://hdl.handle.net/2027.42/128287 http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqm&rft_dat=xri:pqdiss:8907155 |
| Summary: | The choice of a classification scheme is based both on the variance within categories and the discontinuities between categories. This leads to difficulties in classifying biologic taxa that exhibit continuous morphological variation. But, although complete discontinuities in variation are rare, the morphologic distributions may be statistically heterogeneous and rich in information about evolution in time and space. Samples of Early to Middle Miocene Globorotalia from two Southwest Pacific DSDP sites were analyzed in multivariate morphometric space, beginning with a minimum of assumptions about the structure of the sample distributions. The distributions of the DSDP data were compared to morphologies of named species of Globorotalia. Species erected for fossil planktonic foraminifera may be an attempt to categorize complex variation by applying an inappropriate assumption of discrete variation. Morphologic change in chamber shape was measured from medial axis analysis of the chambers and variation in parameters of the coiling geometry were obtained from two point registration of landmarks taken on the test. Principal component analysis indicates that there are three major components of chamber shape variation for these forms. These components do not differ among the data sets examined. Decomposition of landmark transformation into uniform and nonuniform components allows identification of parameters of shape change, examination of variation in known parameters of abstract geometry, and evaluation of their relative importance. The major components of landmark variation incorporate several parameters of abstract spiral geometry, such as angle of increment and expansion rate, as well as other types of shape variation, such as chamber orientation and aperture shape. These components are the same for each data set examined. Within the morphologic spaces defined by these components, the distribution of sampled individuals is generally continuous, but the shape of the distributions and the areas of morphologic space ... |
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