ABR: Phylogenetic Relationships of the Freshwater Genera ofthe Centric Diatom Family Thalassiosiraceae

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In an Accomplishment-Based Renewal of his pioneering cladistic and morphometric studies of diatoms, Dr. Edward Theriot of Philadelphia's Academy of Natural Sciences will examine two major groups of freshwater diatoms of the northern hemisphere, studying both fossil and living forms to determine patterns of evolutionary change. Morphological variability in diagnostic cell-wall features will be examined by light- and electron- microscopy in conjunction with statistical analyses. Reliable identification of diatom species will facilitate both basic taxonomic classification as well as stratigraphic interpretation of geological sediments, thus benefitting oil company geologists and paleontologists. Diatoms are among the most widespread and ecologically important plants in the world, despite their small size. They contribute significantly to photosynthesis in lakes and oceans as well as to geochemical cycling of silicon, a constituent of their cell walls. These siliceous cell walls accumulate in dense fossil deposits, providing unique opportunities to assess the record of evolutionary origins and extinctions in a major lineage of plants. Dr. Theriot's work thus provides insight concerning the linkage between climatic events and evolutionary changes during recent Earth history.