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Laura
Holladay "I cannot think of any better way to learn about science and research than by total immersion in a rich and diverse scientific community such as this." |
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Laura
Holladay "I cannot think of any better way to learn about science and research than by total immersion in a rich and diverse scientific community such as this." |
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Ontogenetic Morphometrics of Planktonic Foraminifera: Using X-Radiograph Images to Study Marine Microfossils Foraminifera are single-celled marine organisms that typically secrete calcareous shells called tests. They can be either benthic, living in the ocean floor sediments, or planktonic, free-floating within about 300 feet of the water's surface. Their tests are abundant in the fossil record, and over 60,000 species of foraminifera have been described to date. However, species-level classification of these microfossils can be a difficult task. In addition to the difficulties brought about by their small size (specimens used in this study are about two tenths of a millimeter in diameter), the planktonic forms have a history of rapid evolution and strong mixing of populations. These factors make the boundaries between species relatively indistinct, so classification must be based on a thorough study of morphological characteristics. The planktonic species chosen for this study are planispiral, which means that they grow by adding chambers to their tests in a planar, spiraling fashion. When new, larger chambers are added, they often overlap many of the younger, smaller chambers. The use of X-radiograph images (X-rays) allows study of the ontogeny, or growth history, of these foraminifera by revealing internal structures of the shell that have been hidden by later growth stages. In this study, four potentially distinct species with similar appearances were compared using morphometric analysis, or measurements of certain characteristics visible in the X-ray images. The specimens were Eocene in age (about 40 million years old), and they were collected from a variety of sites, including sediments from Mexico, New Jersey, and the Tropical Pacific. The resulting data support the division of the species Pseudohastigerina micra, P. naguewichensis, and possibly a third, unnamed morphospecies. The fourth potential species, however, is too similar to P. micra to be named as a distinct new species. This research was supported by a grant from the Smithsonian Women's Committee. |